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Importance of dissolution process on systemic availability of drugs delivered by colon delivery system
Journal of Controlled Release 50 (1998) 111–122
Importance of dissolution process on systemic availability of drugs delivered by colon delivery system Tomohiro Takaya a , Kiyoshi Niwa a , Motoki Muraoka a , Ikuo Ogita a , Noriko Nagai a , a a a b a, Ryo-ichi Yano , Go Kimura , Yukako Yoshikawa , Hiroshi Yoshikawa , Kanji Takada * b
a Department of Pharmaceutics and Pharmacokinetics, Kyoto Pharmaceutical University, Yamashina-ku, Kyoto, 607, Japan Department of Drug Dosage Form Design, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama, 930 -01, Japan
Received 10 January 1997; received in revised form 21 May 1997; accepted 6 June 1997
Abstract The relationship between in vitro drug release characteristics from colon delivery systems and in vivo drug absorption was investigated using three kinds of delayed-release systems. 5-aminosalicylic acid (5-ASA), tegafur (FT) and carbamazepine (CBZ) were selected as model drugs. Pressure-controlled colon delivery capsules (PCC) for liquid preparations, timecontrolled colon delivery capsules (TCC) for liquid and solid preparations and Eudragit S coated tablets for solid preparations were used in this study. At first, in vitro dissolution tests for all preparations were performed. Drug release from solid preparations was delayed compared to that from liquid preparations with all three drugs. Next, these preparations were administered to fasted beagle dogs. For 5-ASA, the mean Cmaxs (peak level) of Eudragit S coated tablets and PCC were 5.52 and 16.89 mg ml 21 , respectively. The mean T maxs (time when drug reached peak level) were 3.0 and 5.3 h. AUCs were 22.57 and 48.09 mg?h ml 21 , respectively. For FT, Cmaxs of Eudragit S coated tablet and PCC were 0.87 and 1.46 mg ml 21 , and T maxs were 7.0 and 6.7 h, respectively. AUCs were 9.73 and 15.55 mg?h ml 21 and bioavailabilities were 43.79 and 70.84%. For CBZ, the mean Cmaxs of liquid preparations and solid preparations were 0.37 and 0.22 mg ml 21 , respectively. The mean T maxs were 4.7 and 4.3 h. AUCs were 0.673 and 0.392 mg?h ml 21 . With liquid preparations, drug was thought to contact to the colonic membrane easily because of lack of interference by stools, and to be absorbed well as compared with solid preparations. From these findings, drug release from colon delivery systems and drug dissolution in the colonic lumen are very important factors for the systemic availability of drugs from the colon delivery systems. 1998 Elsevier Science B.V. Keywords: Colon delivery; Dissolution test; Eudragit S; Pressure-controlled colon delivery capsule; Time-controlled colon delivery system
1. Introduction Colon delivery systems are thought to be effective *Corresponding author. Tel: 181 75 5954626; fax: 181 75 5956311; e-mail: [email protected]
devices for the oral delivery of peptide / protein drugs or drugs used for the treatment of colon diseases, such as Crohn’s disease or ulcerative colitis. Many colon delivery systems have been developed especially for such purposes [1–12]. Recently, we have developed two kinds of colon delivery capsules made
0168-3659 / 98 / $19.00 1998 Elsevier Science B.V. All rights reserved. PII S0168-3659( 97 )00123-5
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of a water-insoluble polymer, ethylcellulose (EC), i.e. pressure-controlled colon delivery capsules (PCC) [13] and time-controlled colon delivery capsules (TCC) [14]. We have reported the application of these systems using two model drugs, recombinant human granulocyte colony-stimulating factor (rhG-CSF), a protein drug [13] and 5-ASA, a drug used for inflammatory bowel disease [15]. Furthermore, the effects of food intake on the delivery efficiency of drug to the colon using these capsules was investigated [16]. In the colon, the viscosity of the luminal content increases due to the reabsorption of water from the lumen [17]. As a result of peristalsis in the colon, higher pressures occur there as compared to pressures in the small intestine. When the EC layer thickness is increased in the PCC capsule so as not to disintegrate in the stomach and small intestine, it passes into the colon. There, due to increased colonic inner pressures, the PCC capsule disintegrates and releases drug in the colonic lumen. These capsules can contain drug molecules either in solution and / or in a solid state where a suppository base has been formulated [13,14]. On the other hand, the mechanism of the disintegration of TCC is due to the balance between the swelling pressure of the formulated low-substituted hydroxypropylcellulose (L-HPC) and the strength or tolerability of the EC cap after the gastrointestinal fluid is introduced inside the TCC through the micropores made at the bottom of the capsule body. This capsule can contains both drug powder and / or drug in suppository base [14]. However, considering the physiological condition of the gastrointestinal tract, less water is present in the colon than in the small intestine. Olsson et al. reported that a matrix controlled-release tablet containing morphine showed limited absorption from both the large intestine and distal parts of the small intestine [18], i.e., drug dissolution and / or release rate from colon delivery devices is thought to be generally decreased in the colon. Therefore, dissolution and release rate is thought to be the rate-limiting process for the bioavailability (BA) of drugs administered by colon delivery devices. To elucidate the role of the dissolution process, three kinds of formulations were used in our study, namely (1) a pH-dependent system, (2) a time-controlled release system and (3) a pressure-controlled release system.
For a pH-dependent system, Eudragit S was used as a coating material to deliver 5-ASA to the lower gastrointestinal tract, as it dissolves at pH 7 [19]. For a time-controlled release system, TCC was used since it can contain the drug in solid state, i.e., as a powder. By comparing the dissolution rate of drugs from PCC, TCC and Eudragit S coated tablet, it was possible to elucidate the effect of dissolution process on the systemic availability of drugs from colon delivery systems. In this report, in vitro dissolution studies and in vivo pharmacokinetic studies were performed using three model drugs such as 5-ASA, tegafur (FT) and carbamazepine (CBZ) having different physicochemical characteristics and the importance of the dissolution process of these drugs from the colon delivery systems on the systemic availability was investigated in beagle dogs.
2. Materials and methods
2.1. Materials 5-ASA and tetra-n-butyl ammonium chloride were obtained from Tokyo Kasei Kogyo Co., Ltd. (Tokyo, Japan). Tegafur (FT) was obtained from Fuji Kagaku Kogyo Co., Ltd. (Toyama, Japan). Carbamazepine (CBZ) was obtained from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Gelatin capsule ([00) was obtained from Yoshida Co., Ltd. (Himeji, Japan). EC (7G, 10G and 100G grades) and L-HPC (LH-11 and LH-20 grades) were gifts from Shin-etsu Chemical Industry Co., Ltd. (Tokyo, Japan) Eudragit ¨ S TM (Rohm Pharm, Dramstadt, Germany) was obtained through Higuchi Inc. (Tokyo, Japan). Propylene glycol (PG), polyethylene glycols (PEG) 1500 and 4000, polyoxyethylene sorbitan monooleate (Tween 80), lactose and triethyl citrate were obtained from Nacalai Tesque Inc. (Kyoto, Japan). Crystalline cellulose was obtained from Asahi Kasei Kogyo Co., Ltd. (Tokyo, Japan). Witepsol TM (S-55 grade) was a gift from Mitsuba Trade Co., Ltd. (Tokyo, Japan). Polyoxyethylated, 60 mmol, castor oil derivative (HCO-60) was obtained from Nikko Chemicals Co., Ltd. (Tokyo, Japan). Male beagle dogs (8.0–13.5 kg) used in this study and standard solid meal of commercial food (LABO D stock TM )
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were obtained from Nippon Nousan Co., Ltd. (Yokohama, Japan). All other materials were of reagent grade and were used as received.
2.2. Test preparations All test preparations used in this study are listed in Table 1. Two kinds of preparations were made for each model drug. For 5-ASA, Eudragit S coated tablets prepared under two compression forces, 20 and 100 kg cm 22 , were used as a solid preparation, and PCCs containing a PG solution of 5-ASA were used as a liquid preparation. For FT, Eudragit S coated tablets prepared with the compression forces of 20 and 100 kg cm 22 were used as a solid preparation, and PCCs containing FT in PEG as a liquid preparation were used. For CBZ, TCCs containing a physical mixture of CBZ and lactose, or a CBZ suspension in Witepsol were used.
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film of Eudragit S was prepared. The tablets were prepared using a reciprocating press (Potassium bromide press, Shimadzu Co., Kyoto, Japan) with a flat-faced punch and a die. At first, 5-ASA and crystalline cellulose (1:1, w / w) or FT and crystalline cellulose (1:25, w / w) were mixed well in a mortar. Then, these mixtures were filled into a die with a diameter of 13 mm, and each tablet was compressed at the applied force of 20 or 100 kg cm 22 and a compression time of 0.5 min. The mean hardnesses were 4862 and 11163 newton for 5-ASA tablets made with 20 and 100 kg cm 22 compression forces, respectively. Also the hardnesses were 5163 and 11564 newton for FT tablets made with 20 and 100 kg cm 22 compression forces, respectively. The weights of the test tablets were 500 mg for 5-ASA and 200 mg for FT, respectively. The tablets were coated using Eudragit S film by means of concentrated Eudragit S solution, glue, prepared by the mixture of methylene chloride and methanol.
2.3. Preparation of Eudragit S coated tablet 2.4. Preparation of PCC Five-hundred and fifty mg of Eudragit S was dissolved in 10 ml of a mixture of methylene chloride and methanol (4:1). To this solution, 400 ml of triethyl citrate was added as a plasticizer. The solution was poured into a petri dish with a diameter of 9.3 cm. The solvent was then removed by evaporation overnight at 68C in a refrigerator, and a
PCCs were prepared as reported previously [13]. Briefly, 600 mg of EC was dissolved in 16 ml of a mixture of methylene chloride and methanol (4:1) by stirring. To both the body and cap of the [00 gelatin capsule, 1.0 and 0.55 ml of the prepared EC solution was added, respectively. The solvent was removed
Table 1 Test preparations used in this study Drug
Drug content (mg)
Compression force (kg cm 22 )
Test preparation
Additive / base
Coating material
5-ASA
250 250 250 10 10 10 50 50
20 100 20 100 -
Eudragit S coated tablet Eudragit S coated tablet PCC Eudragit S coated tablet Eudragit S coated tablet PCC TCC TCC
crystalline cellulose crystalline cellulose PG crystalline cellulose crystalline cellulose PEG mixture lactose Witepsol
Eudragit Eudragit EC Eudragit Eudragit EC
FT
CBZ
5-ASA: 5-aminosalicylic acid. FT: tegafur. CBZ: carbamazepine. PG: propylene glycol. EC: ethylcellulose. PCC: pressure-controlled colon delivery capsule. TCC: time-controlled colon delivery capsule.
S S S S
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by evaporation overnight at 68C in a refrigerator. A 1 mm diameter pore was mechanically made at the top of the cap. After the cap was attached to the body, the PCC was filled with drug solution through the pore. The capsule was then sealed with concentrated EC solution. For 5-ASA containing capsules, a solution was prepared as follows: Two hundred mg of HCO-60 and 3.2 ml of PG were stirred in a beaker with warming at 408C. One gram of 5-ASA was added to this solution and was suspended. For FT containing capsules, a solution was prepared as follows. Four ml of a mixture of PEGs 1500 and 4000 (4.5–1, w / w) was stirred with warming. Five mg of FT was added to the PEG mixture and was completely dissolved.
2.5. Preparation of FT solution for i.v. injection One mg of FT was dissolved in 2 ml of sterile saline with stirring. After FT was dissolved completely, the solution was filtered through a membrane filter (pore size, 0.22 mm). The concentration of this solution was 0.5 mg ml 21 . This i.v. solution was prepared just before administration.
2.6. Preparation of TCC TCC was prepared according to the method described previously [14]. The [00 EC capsule body and a drug container, which just fits the inside of the [00 capsule body, were prepared. The mean thickness was approximately 110 mm. At the bottom of the [00 EC body, four micropores of 400 mm diameter were mechanically made. The inside surface of [00 gelatin caps were also coated with EC (10G grade) of which the mean thickness was 63.165.0 (S.E.) mm. This coated cap was used without dissolving the gelatin. After swellable substances (60 mg of L-HPC, LH-20 grade and 60 mg of L-HPC, LH-11 grade) were filled into the [00 EC body, the drug container was introduced into the body. The EC coated gelatin cap was attached to the body and was sealed by means of EC glue. The drug containers were filled with either the physical mixture of 50 mg of CBZ and 400 mg of lactose as a solid preparation or 50 mg of CBZ suspended with
0.5 ml of Witepsol S-55 at 408C as a liquid preparation.
2.7. In vitro dissolution test Dissolution tests were carried out with the eight preparations as shown in Table 1 using the JPXIII paddle method with 900 ml of 0.067 M phosphate buffer (pH 7.0) or 0.067 M phosphate buffer (pH 7.0) containing 0.2% of Tween 80 at 378C. In the case of Eudragit S coated tablets, the plain tablets were used for the dissolution experiment before the Eudragit S coating was performed, because it takes a few minutes for the Eudragit S film to be dissolved. The rotation speed was set at 100 rpm. The amount of drug dissolved in the medium was determined by measuring the absorbance at 254 nm for 5-ASA, at 270 nm for FT and at 285 nm for CBZ, respectively. All tests were performed in triplicate.
3. Animal experiment
3.1. Oral administration study Three adult male beagle dogs were fasted overnight for at least 12 h in each experiment, although free access to water was allowed. However, during the course of the experiment, water was not given until 6 h after the test preparation was administered. Each dog received one tablet or one capsule in all the studies. At 6 h after administration, a solid meal of commercial food, 150 g, and water were given. No additional food was given during the study. All the experiments were carried out at the same time of the day, to exclude influences by circadian rhythm. The administration was done at 10:30 A.M. with 20 ml of water. At 30 min before drug administration, a control blood sample (0.4–1 ml) was removed from the jugular vein. After oral administration of the test preparation, blood samples were collected. For the 5-ASA study, the dose of 5-ASA was 25 mg kg 21 of body weight. Blood, 1.0ml, was sampled at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 12 h after administration. Plasma was immediately obtained by centrifuging the blood samples at 12 000 rpm for 5 min. For FT study, the dose was 1 mg kg 21 of body weight. Blood, 0.6 ml, was sampled at 1, 2, 3, 4, 5, 6, 7, 8, 10, 12 and 24 h.
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Blood was left for 30 min and serum was obtained by centrifuging at 12 000 rpm for 30 min. For CBZ study, the dose was 5 mg kg 21 of body weight. Blood, 0.4 ml was sampled at 1, 2, 3, 4, 5, 6, 7 and 8 h. The plasma was immediately obtained by centrifuging the blood samples at 12 000 rpm for 5 min. All samples were immediately frozen in a freezer at 2208C until analysis.
3.2. I.V. administration of FT Intravenous (i.v.) administration was done at 10:30 A.M. from the left jugular vein. The dose of FT was 0.25 mg kg 21 of body weight. At 30 min before drug administration, 0.6 ml of blood was removed from the right jugular vein as a control sample. After i.v. administration of the FT solution, 0.6 ml of the blood samples were collected. The sampling schedule was at 5, 10, 15, 30, 45 min, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10, 12 and 24 h. After the obtained blood was left at room temperature for 30 min, serum samples were obtained by centrifuging at 12 000 rpm for 30 min. The serum samples were frozen in a freezer at 2208C until analysis. Other conditions were the same as in the oral administration study.
4. Analytical procedure
4.1. Plasma 5 -ASA concentration The analytical method of 5-ASA reported by Pellicciari et al. [20] was modified. Four hundred ml aliquots of the dog plasma in a 1.5 ml disposable centrifuge tube was treated in a water bath at 908C for 10 min in order to denature the plasma protein components. After centrifuging at 14 000 rpm for 30 min, the plasma water fraction was obtained. One hundred ml of this water fraction was directly injected into a HPLC system fitted with column switching equipment. The HPLC system for 5-ASA analysis consisted of two pumps: P1, Shimadzu LC10AS pump (Kyoto, Japan); and P2, Shimadzu LC3A pump. The UV detector was a Shimadzu SPD10A connected to a Shimadzu C-R4A Chromatopac data processor. For column switching, a motor-actuated six-port column-switching valve (Kyoto Chromato Co. Ltd., Kyoto, Japan) was used. Samples
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were injected using a Toso AS-8010 automatic sample injector. The pre-column (4.0 mm i.d.310 mm length) was dry-packed with Chemcosorb 5ODS-H (Chemco Scientific Co., Ltd., Osaka, Japan). The analytical column was also a Chemcosorb 5ODS-H (4.6 mm i.d.3250 mm length) and was maintained at 608C for all separations. The compositions of the two mobile phases were as follows: mobile phase 1, 0.067 M phosphate buffer (pH 6.0): methanol (90:10, v / v) containing 2 mM tetra-nbutylammonium chloride; mobile phase 2, 0.067 M phosphate buffer (pH 6.0): methanol (92:8, v / v) containing 2 mM tetra-n-butylammonium chloride. The deproteinized sample was loaded into the precolumn and 5-ASA was first adsorbed on the precolumn with mobile phase 2 over a period of 1.5 min (T1). Thereafter, the line was switched to mobile phase 1. 5-ASA was desorbed from the pre-column and transferred to an analytical column with mobile phase 1. The flow-rates of the pumps P1 and P2 were 1.0 ml min 21 and 0.5 ml min 21 , respectively. After 0.75 min had passed from the switching (T2), the mobile phase 1 was removed from the pre-column by mobile phase 2 and the HPLC system was ready for a new cycle. 5-ASA eluted from the analytical column was detected by UV absorption monitored at 254 nm. The plasma 5-ASA concentrations were determined from the calibration curve. The mean extraction efficiency of 5-ASA from plasma was 71.3%. The standard curve of 5-ASA added to the dog plasma was linear over the range of 0.1–20 mg ml 21 and passed through the origin.
4.2. Serum FT concentration To a 15 ml extraction tube, 250 ml of serum sample, 100 ml of 0.5 M NaH 2 PO 4 , 750 ml of distilled water and 4 ml of ethyl acetate was added. The tube was shaken for 10 min and centrifuged at 3000 rpm for 10 min. The ethyl acetate extracts were separated by freezing the water phase for 5 min, followed by decanting the organic phase into a clean glass tube. To this water phase, 4 ml of ethyl acetate was added and the ethyl acetate extraction was performed again. Each ethyl acetate extract was combined and evaporated to dryness. The residue was dissolved in 100 ml of the mobile phase. Twenty
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five ml of this fraction was injected into the HPLC system. The same HPLC apparatus for 5-ASA analysis was used for FT analysis. The analytical column was maintained at 558C for all separations. The composition of the mobile phase 1 and 2 was a mixture of acetonitrile and deionized water (10:90, v / v); the pH was adjusted at 3.0 with trifluoroacetic acid. The flow-rates of the pumps P1 and P2 were 0.8 and 0.5 ml min 21 , respectively. Both column switching times (T1 and T2) were set to 0.5 min. FT eluted from the analytical column was detected by UV absorption monitored at 270 nm. The concentrations of FT in the serum samples were determined from the calibration curve. The mean extraction efficiency of FT from plasma was 90.5%. The standard curve of FT added to the dog serum was linear over the range of 0-2.0 mg ml 21 and passed through the origin.
4.3. Plasma CBZ concentration To a 15 ml extraction tube, 200 ml of plasma sample, 8 ml of methylene chloride, 1 ml of ethyl acetate and 0.067 M phosphate buffer (pH 6.0) were added. The tube was shaken for 10 min and centrifuged at 3000 rpm for 10 min. After removing the aqueous phase, the organic phase was evaporated to dryness. The residue was dissolved in 200 ml of the mobile phase. Eighty ml of this fraction was injected into the HPLC system. The same HPLC apparatus for 5-ASA analysis but without column switching equipment was used for the CBZ analysis. The column was maintained at 558C for separation. The composition of the mobile phase was as follows: deionized water:acetonitrile:tetrahydrofuran (70:26:4, v / v). The flow-rate was 1.0 ml min 21 . CBZ eluted from the analytical column was detected by UV absorption monitored at 285 nm. The concentrations of CBZ in the plasma samples were determined from the calibration curve. The standard curve of CBZ added to the dog plasma was linear over the range of 0–1.0 mg ml 21 and passed through the origin.
5. Pharmacokinetic analysis The following pharmacokinetic parameters were
determined from the plasma or serum drug concentration-time data. Cmax was the maximum drug concentration and T max was the time taken to reach Cmax . The area under the plasma or serum drug concentration vs. time curve (AUC) and the area under the first-moment curve (AUMC) after i.v. and / or oral administrations were calculated using the linear trapezoidal rule up to the last measured plasma or serum drug concentration. The mean residence time (MRT) after oral administration was calculated by AUMC /AUC. The extent of bioavailability (BA) was calculated from the Dose i.v ., Dose oral , AUCi.v. and AUCoral by the following equation, BA5 AUCoral ?Dose i.v. /AUCi.v.?Dose oral .
6. Statistics All values are expressed as their mean6S.E. Statistical differences were assumed to be reproducible when P,0.05 (one-sided t-test).
7. Results
7.1. In vitro dissolution tests Dissolution tests were performed on the eight preparations listed in Table 1, where 5-ASA was used as a representative hydrophilic drug, and FT and CBZ were chosen as representative hydrophobic drugs. Results are shown in Figs. 1–3. Fig. 1 presents the results of 5-ASA dissolution studies. As the release of drug from the PCC needs the physical disintegration of the capsule, dissolution study was performed after small debris was made on PCC. The dissolution of 5-ASA from PCC was very fast and was completed within 2 min. However, the dissolution of 5-ASA from tablets made by a compression force of 20 kg cm 22 was delayed as compared to PCC. At 2 min, after the beginning of dissolution tests, only about 90% of 5-ASA was released; almost 4 min was required for complete release. When the tablet compression force was high, i.e., 100 kg cm 22 , the dissolution rate of 5-ASA from the tablet was further delayed. Half the amount of 5-ASA was released at 2 min and it took 10 min for 5-ASA to be released completely. In the case of FT where the
T. Takaya et al. / Journal of Controlled Release 50 (1998) 111 – 122
Fig. 1. Comparison of the release profiles of 5-ASA from PCC and tablets. j: 5-ASA suspension in PCC, d: 5-ASA tablet (compression force520 kg cm 22 ), m: 5-ASA tablet (compression force5100 kg cm 22 ). Each point represents the mean6S.E. (n5 3).
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same kinds of preparations (tablets and PCC) were used, almost the same results were obtained as with 5-ASA (Fig. 2). The release of FT from PCC was completed within 2 min. However, the release of FT from tablets (compression force520 kg cm 22 ) finished only at 6 min after the start of dissolution tests. Furthermore, the dissolution of FT from the tablets (compression force5100 kg cm 22 ) were not completed even at 20 min. In CBZ studies, similar results were obtained (Fig. 3). The dissolution of CBZ from TCCs containing a CBZ suspension with Witepsol was completed within 6 min. However, the release of CBZ from TCCs containing a physical mixture of CBZ and lactose was not completed within 20 min. Dissolution rate of CBZ from the drug container varied, which was ascribed to the state of drug in the container (i.e., whether the drug molecules were in the solid state or in suspension / solution).
7.2. Oral administration studies in beagle dogs
Fig. 2. Comparison of the release profiles of FT from PCC and tablets. j: FT solution in PCC, d: FT tablet (compression force520 kg cm 22 ), m: FT tablet (compression force5100 kg cm 22 ). Each point represents the mean6S.E. (n53).
Fig. 3. Comparison of the release profiles of CBZ from drug container of TCC. j: CBZ suspension with Witepsol, d: physical mixture of CBZ and lactose. Each point represents the mean6S.E. (n53).
Fig. 4 shows the plasma 5-ASA concentrationtime curves after oral administration of two kinds of 5-ASA preparations. 5-ASA tablet prepared by the compression force with 100 kg cm 22 was used for this in vivo study, as the tablet with 20 kg cm 22 compression force was fragile. In the case of Eudragit S coated tablets, 5-ASA started to appear in the systemic circulation at 2 h after administration and
Fig. 4. Plasma 5-ASA concentration-time curves after oral administration of two kinds of 5-ASA preparations to beagle dogs, 25 mg / kg. The broken lines represent the plasma 5-ASA concentration-time curves of three dogs after oral administration of 5-ASA Eudragit S preparation. The solid lines represent the plasma 5-ASA concentration-time curves of three dogs after administration of PCC containing 5-ASA solution with PG.
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the mean T max was 3.0 h, where the mean Cmax was 21 5.5261.70 mg ml . On the other hand, in the case of 5-ASA in PCCs, the mean T max was 5.360.9 h 21 and Cmax was 16.8961.74 mg ml . The mean colon arrival time of PCCs in fasted beagle dogs was reported to be about 3.3 h in our previous paper [15]. Since 5-ASA was detected in dog plasma from 4 h after administration, it was suggested that 5-ASA was delivered to the colon by the PCC system, and that the PCC disintegrated and released the 5-ASA suspension there. The intra individual variation of plasma 5-ASA levels in the Eudragit S coated tablet group was larger than that in the PCC group. The pharmacokinetic parameters of 5-ASA are listed in Table 2. The T max of Eudragit S coated tablets was shorter than that of PCCs by 2.3 h. On the other hand, the Cmax of 5-ASA from PCCs was about three fold higher than that from Eudragit S coated tablets, and the AUC values of 5-ASA from PCCs was about two fold higher than that of Eudragit S coated tablets. The same studies were performed with the second model drug, FT, at a dose of 1 mg / kg. Fig. 5 shows the serum FT concentration-time curves after the administration of two kinds of FT preparations. According to the same reason in the case of 5-ASA, FT tablet prepared with 100 kg cm 22 compression force was used for this study. FT started to appear in the serum at 2 h after administration of FT Eudragit S coated tablets and serum FT concentrations increased gradually 7 h where it reached its Cmax . The mean Cmax was 0.8760.21 mg ml 21 . Next, PCCs containing FT dissolved in a PEG mixture were
Fig. 5. Serum FT concentration-time curves after i.v. (0.25 mg / kg) or oral (1 mg / kg) administrations of two kinds of FT preparations to beagle dogs. The dotted lines represent the serum FT concentration-time curves of three dogs after i.v. administration of FT solution. The broken lines represent the serum FT concentration-time curves of three dogs after oral administration of FT Eudragit S preparation. The solid lines represent the serum FT concentration-time curves of three dogs after oral administration of PCC containing FT and PEG as base.
administered to beagle dogs. PEG was selected as a base because it changed to a liquid state after oral administration to dogs (i.e., at body temperature). In this experiment, FT was detected at 3–6 h after administration and FT concentration increased rapidly as compared with Eudragit S coated tablets. The mean T max was 6.6760.88 h and the Cmax was 1.4660.22 mg ml 21 . The i.v. injection of FT was performed in the same dogs in order to estimate the systemic availability of FT. These results are also
Table 2 Pharmacokinetic parameter values obtained after oral administration of 5-ASA to beagle dogs, 25mg / kg Test
Pharmacokinetic parameter
preparation
Cmax (mg / ml)
Eudragit S coated tablet PCC
T max (h)
AUC (mg?h / ml)
MRT (h)
5.5261.70
3.060.0
22.5766.15
4.5160.22
16.8961.74
5.360.9
48.0969.3 8
6.2260.34
Cmax : maximum plasma drug concentration. T max : the time when the plasma drug concentration reaches to its maximum concentration. AUC: area under the plasma drug concentration vs. time curve. MRT : mean residence time. Each point represents the mean6S.E. (n53). *: Statistically significant difference (P,0.05).
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Table 3 Pharmacokinetic parameter values obtained after i.v. and oral administrations of FT to beagle dogs Test
Pharmacokinetic parameter
preparation
Dose (mg / kg)
Cmax (mg / ml)
T max (h)
i.v. solution Eudragit S coated tablet PCC
0.25
0.7360.03
0.0
5.5560.69
8.1660.32
1.0
0.8760.21
7.060.6
9.7361.73
10.5960.22
43.7967.80
1.0
1.4660.22
6.760.9
15.5560.25
11.3460.78
70.8460.35
AUC (mg?h / ml)
MRT (h)
BA (%) 100
BA: extent of bioavailability. Each value represents the mean6S.E. (n53). *: Statistically significant difference (P,0.05).
shown in Fig. 5. The pharmacokinetic parameter values of FT are shown in Table 3. There was no significant difference in the T max and Cmax between the two preparations. However, there was a signifi-
Fig. 6. Plasma CBZ concentration-time curves after oral administration of two kinds of CBZ preparations to beagle dogs, 5 mg / kg. The broken lines represent the plasma CBZ concentration-time curves of three dogs after oral administration of FT Eudragit S preparation. The solid lines represent the plasma CBZ concentration-time curves of three dogs after administration of TCC containing a suspension of CBZ with Witepsol.
cant difference in the AUC values between these preparations. The BA value of FT from Eudragit S coated tablets was 43.7967.80% and that from PCC was 70.8460.35%. There was a significant difference between these two BA values. Finally, the systemic availability of CBZ was investigated where another system, namely TCC, was used. In this study, CBZ was filled into the drug container capsule of TCC in two forms. One form consisted of a physical mixture of CBZ and lactose in a solid state. The second form was a suspension of CBZ with Witepsol. Fig. 6 shows the results of these studies and pharmacokinetic parameter values are listed in Table 4. In both preparations, CBZ appeared in the systemic circulation at 3–4 h after administration, and the mean T maxs were 4.360.3 and 4.760.3 h, respectively. There was no significant difference between the two preparations. The mean Cmaxs were 0.2260.02 and 0.3760.05 mg ml 21 , respectively. The Cmax of the suspension was significantly higher than Cmax of solid preparation. AUC values were 0.39260.058 and 0.67360.019 mg?h ml 21 , respectively.
Table 4 Pharmacokinetic parameter values obtained after oral admiration of CBZ to beagle dogs, 5mg / kg Test
Pharmacokinetic parameter
preparation
Cmax (mg / ml)
T max (h)
AUC (mg?h / ml)
MRT (h)
Physical mixture Witepsol suspension
0.2260.021 0.3760.05
4.360.3 4.760.3
0.39260.058 0.67360.019
4.6060.32 4.6060.42
Each value represents the mean6S.E. (n53). *: Statistically significant difference (P,0.05).
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8. Discussion In this paper, in vitro dissolution tests and in vivo pharmacokinetic studies were performed on solid and liquid preparations in colon delivery systems using three model drugs representing both hydrophilic and hydrophobic compounds. The correlation between the release rate of drugs from the colon delivery systems and the systemic availability of drugs from the colon was studied. Colon delivery systems have been the focus of much attention recently because they are thought to be effective devices for oral dosing of peptide / protein drugs. In addition, they allow for optimal delivery of drugs designed to act on the colonic lumen, such as drugs for inflammatory bowel disease. Since a report concerning the use of azo-polymer for colon delivery system by Saffran in 1986 [1], many investigators have been engaged in developing colon delivery systems [2–12]. Recently, we have developed two kind of colon delivery capsules, namely PCC and TCC and reported their applications to a representative protein drug, rhGCSF [13], drugs for inflammatory bowel disease, 5-ASA [15] and fluorescein [13,16]. The characteristics of PCC are as follows: (1) PCC is made of EC, which has been used as pharmaceutical adjuvant for a long time, and therefore its safety is well established. (2) PCC can contain drug in solution or suspension in suppository base. (3) Drug release occurs instantaneously by physical destruction in the colon due to inner pressure. (4) Drug release from PCC is independent of pH in the gastrointestinal tract. (5) Drug release is independent of the gastrointestinal transit time. (6) PCC is prepared easily. On the other hand, TCC has some characteristics as follows. (1) TCC is also made of EC. (2) TCC can contain drug powder or drug in suppository base. (3) Drug release from TCC is dependent on the time, i.e., TCC releases drug at predetermined time. Initially, 5-ASA was used as a hydrophilic model drug. As 5-ASA is rapidly absorbed from the small intestine after oral administration, SASP, its prodrug, has been used in clinical stages over 50 years [21]. However, some 5-ASA preparations, such as Olsalazine [22] and Asacol [19], have been developed to overcome the side effects of SASP. Asacol is a 5-ASA tablet which is coated with Eudragit S [19].
The Eudragit S coated tablet used in this experiment is similar to Asacol. As Eudragit S dissolves at a pH greater than 7 [19], Eudragit S coated tablets releases drug at the lower small intestine [23]. Instead of Asacol, two types of Eudragit S coated 5-ASA tablets were prepared in this laboratory. As the compression force used for preparing Asacol was not uncertain, two conditions were tried. As expected, the tablet prepared with low compression force was dissolved faster than that with high compression force. The hardness study suggested that the tablet with compression force of 100 kg cm 22 is conceivable. Therefore, the systemic availability of 5-ASA was compared between tablet and PCC. As shown in Fig. 4, the time for the first appearance of 5-ASA into the systemic circulation from Eudragit S coated tablets was shorter than that from PCCs by 2.3 h. Our previous report showed that mean colon arrival time was 3.3 h in our beagle dogs in the fasted condition [13,14]. On the other hand, it was reported that the pH in the canine small intestine was higher than that of the human [24]. Therefore, the release of 5-ASA from Eudragit S coated tablets was thought to begin in the lower small intestine. On the other hand, PCC was thought to release 5-ASA in the colon. With respect to the Cmax and AUC values, there were significant differences between the two formulations. In the case of Eudragit S coated tablets, solid materials such as stools in the colon decreased both the amount and time of 5-ASA molecules coming in contact with the gut wall. In addition, 5-ASA molecules were not well dissolved by the gastrointestinal fluid because a solid dosage form was used. Therefore, Cmax and AUC values tended to show greater variations. However, since PCCs were filled with 5-ASA in solution, 5-ASA contact with the colonic mucosa occurred easily and 5-ASA was well absorbed there. The same experiment was performed using FT, as a hydrophobic model drug. FT is a derivative of 5-fluorouracil and has been used widely in patients suffering from colorectal cancer. In this study, a PEG mixture was used as a base for the PCCs, as it has been often used as a suppository base. The PEG mixture used in this study is solid at room temperature but becomes liquid after administration when it reaches body temperature. As FT is contained in the
T. Takaya et al. / Journal of Controlled Release 50 (1998) 111 – 122
PCC as solution, the dissolution rate of FT from the PCC was faster than that obtained from the tablet. The PCC containing FT disintegrates at colonic inner pressures as does these containing 5-ASA in PG solution. Therefore, PCC in which PEG was used as a base was favorable from the standpoint of both reservation and handling. In FT studies, similar properties were observed as in 5-ASA studies. However, although the absorption lag-times after the oral administration of the preparations were the same for 5-ASA and FT using Eudragit S coated tablets, the T max of FT after administration of Eudragit S coated tablets was delayed as compared to that of 5-ASA. This is thought to be due to the difference in the ratio of drug to pharmaceutical additive (i.e., crystalline cellulose) in the preparation. In the case of the FT preparation, since the drug ratio was about 3.8% of the total weight, it is thought that the crystalline cellulose bound strongly and the tablet did not easily disintegrate in the lower gastrointestinal tract. On the other hand, the systemic availability of FT delivered by PCCs was higher than that delivered by Eudragit S coated tablet. Since FT dissolved completely within the PEG mixture base, a good systemic availability of FT was obtained from the colon. With respect to the most hydrophobic model drug in this study, CBZ, the physical mixture of CBZ and lactose and the suspension of CBZ with Witepsol were introduced into the drug container of the TCC. As oily base was used to prepare TCC containing CBZ, the dissolution rate of CBZ from TCC was slow as compared to that observed in PCCs containing 5-ASA and / or FT. However, the in vivo systemic availability study using beagle dogs showed that TCC had higher systemic availability than tablet. It has been reported that the length-normalized intestinal permeability for CBZ administered in solution was greater in the colon than in the duodenojejunum by using a single pass perfusion technique [25]. However, CBZ absorption was reported to decrease when an Oros TM osmotic pump was located in the human colon [26]. As shown in Fig. 6, CBZ absorption was significantly increased by administering it as suspension using Witepsol. It is thought that the drug release rate from the drug container was improved by using the Witepsol
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suspension system, and a higher systemic availability was obtained.
9. Conclusions Colon delivery capsules such as PCC containing 5-ASA as suspension, PCC containing FT as solution and TCC containing CBZ as oily solution, showed 2.13, 1.60 and 1.72 times higher systemic availability of each drug than that obtained with Eudragit S coated tablets. In vitro dissolution study showed that the drug release from the colon delivery capsules were faster than that obtained from tablets. There was a correlation between the in vitro dissolution rate of drugs from the colon delivery systems and the in vivo systemic availability of drugs after oral administration to beagle dogs. Therefore, the importance of the dissolution process on the systemic availability of drugs having different physicochemical characteristics, 5-ASA, FT and CBZ, after oral administration to beagle dogs by colon delivery systems has been revealed.
References [1] M. Saffran, G.S. Kumar, C. Savariar, J.C. Burnham, F. Williams, D.C. Neckers, A new approach to the oral administration of insulin and other peptide drugs, Science 233 (1986) 1081–1084. [2] M. Ashford, J.T. Fell, D. Attwood, P.J. Woodhead, An in vitro investigation into the suitability of pH-dependent polymers for colon targeting, Int. J. Pharm. 91 (1993) 241– 245. [3] R. Peters, R. Kinget, Film-forming polymers for colonic drug delivery: I. Synthesis and physical and chemical properties of methyl derivatives of Eudragit S. Int. J. Pharm. 94 (1993) 125–134. [4] P.T. Watts, C.G. Wilson, M.C. Davies, C.D. Melia, Radiolabelling of polymer microspheres for scintigraphic investigations by neutron activation. 4. A pharmacoscintigraphic study of colon-targeted Eudragit RS-sulphapyridine microspheres in human volunteers, Int. J. Pharm. 102 (1994) 101–108. [5] I.R. Wilding, S.S. Davis, F. Pozzi, P. Furlani, A. Gazzaniga, Enteric coated timed release systems for colonic targeting, Int. J. Pharm. 111 (1994) 99–102. [6] M.E.K. Kraeling, W.A. Ritschel, Development of colonic
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T. Takaya et al. / Journal of Controlled Release 50 (1998) 111 – 122 release capsule dosage form and the absorption of insulin, Meth. Find. Clin. Pharmacol. 14 (1992) 199–209. A. Rashid, Dispensing Device, British Patent Application 2230441 A, 15 Feb. 1990. ˇ H. Brøndsted, J. Kopecek, Hydrogels for site-specific drug delivery to the colon: In vitro and in vivo degradation, Pharm. Res. 9 (1992) 1540–1545. C.S. Leopold, D.R. Friend, In vivo pharmacokinetic study for the assessment of poly (L-aspartic acid) as a drug carrier for colon-specific drug delivery, J. Pharmacokin. Biopharm. 23 (1995) 397–406. M. Ashford, J. Fell, D. Attwood, H. Sharma, P. Woodhead, Studies on pectin formulations for colonic drug delivery, J. Control. Release 30 (1994) 225–232. L. Hovgaard, H. Brøndsted, Dextran hydrogels for colonspecific drug delivery, J. Control. Release 36 (1995) 159– 166. S. Milojevic, J.M. Newton, J.H. Cummings, G.R. Gibson, R.L. Botham, S.G. Ring, M. Stockham, M.C. Allwood, Amylose as a coating for drug delivery to the colon: Preparation and in vitro evaluation using 5-aminosalicylic acid pellets, J. Control. Release 38 (1996) 75–84. T. Takaya, C. Ikeda, N. Imagawa, K. Niwa, K. Takada, Development of a colon delivery capsule and the pharmacological activity of recombinant human granulocyte colonystimulating factor (rhG-CSF) in beagle dogs, J. Pharm. Pharmacol. 47 (1995) 474–478. K. Niwa, T. Takaya, T. Morimoto, K. Takada, Preparation and evaluation of a time-controlled release capsule made of ethylcellulose for colon delivery of drugs, J. Drug Targeting 3 (1995) 83–89. T. Takaya, K. Sawada, H. Suzuki, A. Funaoka, K. Matsuda, K. Takada, Application of a colon delivery capsule to 5aminosalicylic acid and evaluation of the pharmacokinetic profile after oral administration to beagle dogs, J. Drug Targeting 4 (1997) 271–276. K. Matsuda, T. Takaya, F. Shimoji, M. Muraoka, Y. Yoshikawa, K. Takada, Effect of food intake on the delivery of fluorescein as a model drug in colon delivery capsule after oral administration to beagle dogs, J. Drug Targeting 4 (1996) 59–67.
[17] S. Rao, W.A. Ritschel, Colonic drug delivery of small peptides, S.T.P. Pharma Sciences 5 (1995) 19–29. [18] B. Olsson, Z.G. Wager, P. Mansion, G. Ragnarsson, A gamma scintigraphic study of the absorption of morphine from controlled-release tablets. Int. J. Pharm. 119 (1995) 223–229. [19] R. Caprilli, A. Andreoli, L. Capurso, G. Corrao, G. D’albasio, A. Gioieni, G. Assuero Lanfranchi, I. Paladini, F. Pallone, V. Ponti, G.P. Rigo, F.P. Rossini, G.C. Sturniolo, F. Tonelli, D. Valpiani, Oral mesalazine (5-aminosalicylic acid; Asacol) for the prevention of post-operative recurrence of Crohn’s disease, Aliment. Pharamacol. Ther. 8 (1994) 35– 43. [20] R. Pellicclari, A. Garzon-Aburbeh, B. Natalini, M. Marinozzi, C. Clerici, G. Gentili, A. Moreili, Brush-border-enzymemediated intestine-specific drug delivery. Amino acid prodrugs of 5-aminosalicylic acid, J. Med. Chem. 36 (1993) 4201–4207. [21] M.A. Peppercorn, P. Goldman, Distribution studies of salicylazosulfapyridine and its metabolises, Gastroenterology 64 (1973) 240–245. [22] A.N. Wadworth, A. Fitton, Olsalazine. A review of its pharmacokinetic properties, and therapeutic potential in inflammatory bowel disease, Drugs 41 (1991) 647–664. [23] S.S. Davis, Small intestinal transit, in: J.G. Hardy, S.S. Davis and C.G. Willson (Eds.), Drug delivery to the gastrointestinal tract, Ellis Horwood Limited, Chichester, England, 1989, p. 49. [24] J.B. Dressman, Comparison of canine and human gastrointestinal physiology, Pharm. Res. 3 (1986) 123–131. [25] L.E. Riad, R.J. Sawchuk, Absorptive clearance of carbamazepine and selected metabolises in rabbit intestine, Pharm. Res. 8 (1991) 1050–1055. [26] I.R. Wilding, S.S. Davis, J.G. Hardy, C.S. Robertson, V.A. John, M.L. Powell, M. Leal, P. Lloyd, S.M. Walker, Relationship between systemic drug absorption and gastrointestinal transit after the simultaneous oral administration of carbamazepine as a controlled-release system and as a suspension of 12 N-labelled drug to healthy volunteers, Br. J. Clin. Pharmacol. 32 (1991) 573–579.
Importance of dissolution process on systemic availability of drugs delivered by colon delivery system Tomohiro Takaya a , Kiyoshi Niwa a , Motoki Muraoka a , Ikuo Ogita a , Noriko Nagai a , a a a b a, Ryo-ichi Yano , Go Kimura , Yukako Yoshikawa , Hiroshi Yoshikawa , Kanji Takada * b
a Department of Pharmaceutics and Pharmacokinetics, Kyoto Pharmaceutical University, Yamashina-ku, Kyoto, 607, Japan Department of Drug Dosage Form Design, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama, 930 -01, Japan
Received 10 January 1997; received in revised form 21 May 1997; accepted 6 June 1997
Abstract The relationship between in vitro drug release characteristics from colon delivery systems and in vivo drug absorption was investigated using three kinds of delayed-release systems. 5-aminosalicylic acid (5-ASA), tegafur (FT) and carbamazepine (CBZ) were selected as model drugs. Pressure-controlled colon delivery capsules (PCC) for liquid preparations, timecontrolled colon delivery capsules (TCC) for liquid and solid preparations and Eudragit S coated tablets for solid preparations were used in this study. At first, in vitro dissolution tests for all preparations were performed. Drug release from solid preparations was delayed compared to that from liquid preparations with all three drugs. Next, these preparations were administered to fasted beagle dogs. For 5-ASA, the mean Cmaxs (peak level) of Eudragit S coated tablets and PCC were 5.52 and 16.89 mg ml 21 , respectively. The mean T maxs (time when drug reached peak level) were 3.0 and 5.3 h. AUCs were 22.57 and 48.09 mg?h ml 21 , respectively. For FT, Cmaxs of Eudragit S coated tablet and PCC were 0.87 and 1.46 mg ml 21 , and T maxs were 7.0 and 6.7 h, respectively. AUCs were 9.73 and 15.55 mg?h ml 21 and bioavailabilities were 43.79 and 70.84%. For CBZ, the mean Cmaxs of liquid preparations and solid preparations were 0.37 and 0.22 mg ml 21 , respectively. The mean T maxs were 4.7 and 4.3 h. AUCs were 0.673 and 0.392 mg?h ml 21 . With liquid preparations, drug was thought to contact to the colonic membrane easily because of lack of interference by stools, and to be absorbed well as compared with solid preparations. From these findings, drug release from colon delivery systems and drug dissolution in the colonic lumen are very important factors for the systemic availability of drugs from the colon delivery systems. 1998 Elsevier Science B.V. Keywords: Colon delivery; Dissolution test; Eudragit S; Pressure-controlled colon delivery capsule; Time-controlled colon delivery system
1. Introduction Colon delivery systems are thought to be effective *Corresponding author. Tel: 181 75 5954626; fax: 181 75 5956311; e-mail: [email protected]
devices for the oral delivery of peptide / protein drugs or drugs used for the treatment of colon diseases, such as Crohn’s disease or ulcerative colitis. Many colon delivery systems have been developed especially for such purposes [1–12]. Recently, we have developed two kinds of colon delivery capsules made
0168-3659 / 98 / $19.00 1998 Elsevier Science B.V. All rights reserved. PII S0168-3659( 97 )00123-5
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of a water-insoluble polymer, ethylcellulose (EC), i.e. pressure-controlled colon delivery capsules (PCC) [13] and time-controlled colon delivery capsules (TCC) [14]. We have reported the application of these systems using two model drugs, recombinant human granulocyte colony-stimulating factor (rhG-CSF), a protein drug [13] and 5-ASA, a drug used for inflammatory bowel disease [15]. Furthermore, the effects of food intake on the delivery efficiency of drug to the colon using these capsules was investigated [16]. In the colon, the viscosity of the luminal content increases due to the reabsorption of water from the lumen [17]. As a result of peristalsis in the colon, higher pressures occur there as compared to pressures in the small intestine. When the EC layer thickness is increased in the PCC capsule so as not to disintegrate in the stomach and small intestine, it passes into the colon. There, due to increased colonic inner pressures, the PCC capsule disintegrates and releases drug in the colonic lumen. These capsules can contain drug molecules either in solution and / or in a solid state where a suppository base has been formulated [13,14]. On the other hand, the mechanism of the disintegration of TCC is due to the balance between the swelling pressure of the formulated low-substituted hydroxypropylcellulose (L-HPC) and the strength or tolerability of the EC cap after the gastrointestinal fluid is introduced inside the TCC through the micropores made at the bottom of the capsule body. This capsule can contains both drug powder and / or drug in suppository base [14]. However, considering the physiological condition of the gastrointestinal tract, less water is present in the colon than in the small intestine. Olsson et al. reported that a matrix controlled-release tablet containing morphine showed limited absorption from both the large intestine and distal parts of the small intestine [18], i.e., drug dissolution and / or release rate from colon delivery devices is thought to be generally decreased in the colon. Therefore, dissolution and release rate is thought to be the rate-limiting process for the bioavailability (BA) of drugs administered by colon delivery devices. To elucidate the role of the dissolution process, three kinds of formulations were used in our study, namely (1) a pH-dependent system, (2) a time-controlled release system and (3) a pressure-controlled release system.
For a pH-dependent system, Eudragit S was used as a coating material to deliver 5-ASA to the lower gastrointestinal tract, as it dissolves at pH 7 [19]. For a time-controlled release system, TCC was used since it can contain the drug in solid state, i.e., as a powder. By comparing the dissolution rate of drugs from PCC, TCC and Eudragit S coated tablet, it was possible to elucidate the effect of dissolution process on the systemic availability of drugs from colon delivery systems. In this report, in vitro dissolution studies and in vivo pharmacokinetic studies were performed using three model drugs such as 5-ASA, tegafur (FT) and carbamazepine (CBZ) having different physicochemical characteristics and the importance of the dissolution process of these drugs from the colon delivery systems on the systemic availability was investigated in beagle dogs.
2. Materials and methods
2.1. Materials 5-ASA and tetra-n-butyl ammonium chloride were obtained from Tokyo Kasei Kogyo Co., Ltd. (Tokyo, Japan). Tegafur (FT) was obtained from Fuji Kagaku Kogyo Co., Ltd. (Toyama, Japan). Carbamazepine (CBZ) was obtained from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Gelatin capsule ([00) was obtained from Yoshida Co., Ltd. (Himeji, Japan). EC (7G, 10G and 100G grades) and L-HPC (LH-11 and LH-20 grades) were gifts from Shin-etsu Chemical Industry Co., Ltd. (Tokyo, Japan) Eudragit ¨ S TM (Rohm Pharm, Dramstadt, Germany) was obtained through Higuchi Inc. (Tokyo, Japan). Propylene glycol (PG), polyethylene glycols (PEG) 1500 and 4000, polyoxyethylene sorbitan monooleate (Tween 80), lactose and triethyl citrate were obtained from Nacalai Tesque Inc. (Kyoto, Japan). Crystalline cellulose was obtained from Asahi Kasei Kogyo Co., Ltd. (Tokyo, Japan). Witepsol TM (S-55 grade) was a gift from Mitsuba Trade Co., Ltd. (Tokyo, Japan). Polyoxyethylated, 60 mmol, castor oil derivative (HCO-60) was obtained from Nikko Chemicals Co., Ltd. (Tokyo, Japan). Male beagle dogs (8.0–13.5 kg) used in this study and standard solid meal of commercial food (LABO D stock TM )
T. Takaya et al. / Journal of Controlled Release 50 (1998) 111 – 122
were obtained from Nippon Nousan Co., Ltd. (Yokohama, Japan). All other materials were of reagent grade and were used as received.
2.2. Test preparations All test preparations used in this study are listed in Table 1. Two kinds of preparations were made for each model drug. For 5-ASA, Eudragit S coated tablets prepared under two compression forces, 20 and 100 kg cm 22 , were used as a solid preparation, and PCCs containing a PG solution of 5-ASA were used as a liquid preparation. For FT, Eudragit S coated tablets prepared with the compression forces of 20 and 100 kg cm 22 were used as a solid preparation, and PCCs containing FT in PEG as a liquid preparation were used. For CBZ, TCCs containing a physical mixture of CBZ and lactose, or a CBZ suspension in Witepsol were used.
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film of Eudragit S was prepared. The tablets were prepared using a reciprocating press (Potassium bromide press, Shimadzu Co., Kyoto, Japan) with a flat-faced punch and a die. At first, 5-ASA and crystalline cellulose (1:1, w / w) or FT and crystalline cellulose (1:25, w / w) were mixed well in a mortar. Then, these mixtures were filled into a die with a diameter of 13 mm, and each tablet was compressed at the applied force of 20 or 100 kg cm 22 and a compression time of 0.5 min. The mean hardnesses were 4862 and 11163 newton for 5-ASA tablets made with 20 and 100 kg cm 22 compression forces, respectively. Also the hardnesses were 5163 and 11564 newton for FT tablets made with 20 and 100 kg cm 22 compression forces, respectively. The weights of the test tablets were 500 mg for 5-ASA and 200 mg for FT, respectively. The tablets were coated using Eudragit S film by means of concentrated Eudragit S solution, glue, prepared by the mixture of methylene chloride and methanol.
2.3. Preparation of Eudragit S coated tablet 2.4. Preparation of PCC Five-hundred and fifty mg of Eudragit S was dissolved in 10 ml of a mixture of methylene chloride and methanol (4:1). To this solution, 400 ml of triethyl citrate was added as a plasticizer. The solution was poured into a petri dish with a diameter of 9.3 cm. The solvent was then removed by evaporation overnight at 68C in a refrigerator, and a
PCCs were prepared as reported previously [13]. Briefly, 600 mg of EC was dissolved in 16 ml of a mixture of methylene chloride and methanol (4:1) by stirring. To both the body and cap of the [00 gelatin capsule, 1.0 and 0.55 ml of the prepared EC solution was added, respectively. The solvent was removed
Table 1 Test preparations used in this study Drug
Drug content (mg)
Compression force (kg cm 22 )
Test preparation
Additive / base
Coating material
5-ASA
250 250 250 10 10 10 50 50
20 100 20 100 -
Eudragit S coated tablet Eudragit S coated tablet PCC Eudragit S coated tablet Eudragit S coated tablet PCC TCC TCC
crystalline cellulose crystalline cellulose PG crystalline cellulose crystalline cellulose PEG mixture lactose Witepsol
Eudragit Eudragit EC Eudragit Eudragit EC
FT
CBZ
5-ASA: 5-aminosalicylic acid. FT: tegafur. CBZ: carbamazepine. PG: propylene glycol. EC: ethylcellulose. PCC: pressure-controlled colon delivery capsule. TCC: time-controlled colon delivery capsule.
S S S S
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by evaporation overnight at 68C in a refrigerator. A 1 mm diameter pore was mechanically made at the top of the cap. After the cap was attached to the body, the PCC was filled with drug solution through the pore. The capsule was then sealed with concentrated EC solution. For 5-ASA containing capsules, a solution was prepared as follows: Two hundred mg of HCO-60 and 3.2 ml of PG were stirred in a beaker with warming at 408C. One gram of 5-ASA was added to this solution and was suspended. For FT containing capsules, a solution was prepared as follows. Four ml of a mixture of PEGs 1500 and 4000 (4.5–1, w / w) was stirred with warming. Five mg of FT was added to the PEG mixture and was completely dissolved.
2.5. Preparation of FT solution for i.v. injection One mg of FT was dissolved in 2 ml of sterile saline with stirring. After FT was dissolved completely, the solution was filtered through a membrane filter (pore size, 0.22 mm). The concentration of this solution was 0.5 mg ml 21 . This i.v. solution was prepared just before administration.
2.6. Preparation of TCC TCC was prepared according to the method described previously [14]. The [00 EC capsule body and a drug container, which just fits the inside of the [00 capsule body, were prepared. The mean thickness was approximately 110 mm. At the bottom of the [00 EC body, four micropores of 400 mm diameter were mechanically made. The inside surface of [00 gelatin caps were also coated with EC (10G grade) of which the mean thickness was 63.165.0 (S.E.) mm. This coated cap was used without dissolving the gelatin. After swellable substances (60 mg of L-HPC, LH-20 grade and 60 mg of L-HPC, LH-11 grade) were filled into the [00 EC body, the drug container was introduced into the body. The EC coated gelatin cap was attached to the body and was sealed by means of EC glue. The drug containers were filled with either the physical mixture of 50 mg of CBZ and 400 mg of lactose as a solid preparation or 50 mg of CBZ suspended with
0.5 ml of Witepsol S-55 at 408C as a liquid preparation.
2.7. In vitro dissolution test Dissolution tests were carried out with the eight preparations as shown in Table 1 using the JPXIII paddle method with 900 ml of 0.067 M phosphate buffer (pH 7.0) or 0.067 M phosphate buffer (pH 7.0) containing 0.2% of Tween 80 at 378C. In the case of Eudragit S coated tablets, the plain tablets were used for the dissolution experiment before the Eudragit S coating was performed, because it takes a few minutes for the Eudragit S film to be dissolved. The rotation speed was set at 100 rpm. The amount of drug dissolved in the medium was determined by measuring the absorbance at 254 nm for 5-ASA, at 270 nm for FT and at 285 nm for CBZ, respectively. All tests were performed in triplicate.
3. Animal experiment
3.1. Oral administration study Three adult male beagle dogs were fasted overnight for at least 12 h in each experiment, although free access to water was allowed. However, during the course of the experiment, water was not given until 6 h after the test preparation was administered. Each dog received one tablet or one capsule in all the studies. At 6 h after administration, a solid meal of commercial food, 150 g, and water were given. No additional food was given during the study. All the experiments were carried out at the same time of the day, to exclude influences by circadian rhythm. The administration was done at 10:30 A.M. with 20 ml of water. At 30 min before drug administration, a control blood sample (0.4–1 ml) was removed from the jugular vein. After oral administration of the test preparation, blood samples were collected. For the 5-ASA study, the dose of 5-ASA was 25 mg kg 21 of body weight. Blood, 1.0ml, was sampled at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 12 h after administration. Plasma was immediately obtained by centrifuging the blood samples at 12 000 rpm for 5 min. For FT study, the dose was 1 mg kg 21 of body weight. Blood, 0.6 ml, was sampled at 1, 2, 3, 4, 5, 6, 7, 8, 10, 12 and 24 h.
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Blood was left for 30 min and serum was obtained by centrifuging at 12 000 rpm for 30 min. For CBZ study, the dose was 5 mg kg 21 of body weight. Blood, 0.4 ml was sampled at 1, 2, 3, 4, 5, 6, 7 and 8 h. The plasma was immediately obtained by centrifuging the blood samples at 12 000 rpm for 5 min. All samples were immediately frozen in a freezer at 2208C until analysis.
3.2. I.V. administration of FT Intravenous (i.v.) administration was done at 10:30 A.M. from the left jugular vein. The dose of FT was 0.25 mg kg 21 of body weight. At 30 min before drug administration, 0.6 ml of blood was removed from the right jugular vein as a control sample. After i.v. administration of the FT solution, 0.6 ml of the blood samples were collected. The sampling schedule was at 5, 10, 15, 30, 45 min, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10, 12 and 24 h. After the obtained blood was left at room temperature for 30 min, serum samples were obtained by centrifuging at 12 000 rpm for 30 min. The serum samples were frozen in a freezer at 2208C until analysis. Other conditions were the same as in the oral administration study.
4. Analytical procedure
4.1. Plasma 5 -ASA concentration The analytical method of 5-ASA reported by Pellicciari et al. [20] was modified. Four hundred ml aliquots of the dog plasma in a 1.5 ml disposable centrifuge tube was treated in a water bath at 908C for 10 min in order to denature the plasma protein components. After centrifuging at 14 000 rpm for 30 min, the plasma water fraction was obtained. One hundred ml of this water fraction was directly injected into a HPLC system fitted with column switching equipment. The HPLC system for 5-ASA analysis consisted of two pumps: P1, Shimadzu LC10AS pump (Kyoto, Japan); and P2, Shimadzu LC3A pump. The UV detector was a Shimadzu SPD10A connected to a Shimadzu C-R4A Chromatopac data processor. For column switching, a motor-actuated six-port column-switching valve (Kyoto Chromato Co. Ltd., Kyoto, Japan) was used. Samples
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were injected using a Toso AS-8010 automatic sample injector. The pre-column (4.0 mm i.d.310 mm length) was dry-packed with Chemcosorb 5ODS-H (Chemco Scientific Co., Ltd., Osaka, Japan). The analytical column was also a Chemcosorb 5ODS-H (4.6 mm i.d.3250 mm length) and was maintained at 608C for all separations. The compositions of the two mobile phases were as follows: mobile phase 1, 0.067 M phosphate buffer (pH 6.0): methanol (90:10, v / v) containing 2 mM tetra-nbutylammonium chloride; mobile phase 2, 0.067 M phosphate buffer (pH 6.0): methanol (92:8, v / v) containing 2 mM tetra-n-butylammonium chloride. The deproteinized sample was loaded into the precolumn and 5-ASA was first adsorbed on the precolumn with mobile phase 2 over a period of 1.5 min (T1). Thereafter, the line was switched to mobile phase 1. 5-ASA was desorbed from the pre-column and transferred to an analytical column with mobile phase 1. The flow-rates of the pumps P1 and P2 were 1.0 ml min 21 and 0.5 ml min 21 , respectively. After 0.75 min had passed from the switching (T2), the mobile phase 1 was removed from the pre-column by mobile phase 2 and the HPLC system was ready for a new cycle. 5-ASA eluted from the analytical column was detected by UV absorption monitored at 254 nm. The plasma 5-ASA concentrations were determined from the calibration curve. The mean extraction efficiency of 5-ASA from plasma was 71.3%. The standard curve of 5-ASA added to the dog plasma was linear over the range of 0.1–20 mg ml 21 and passed through the origin.
4.2. Serum FT concentration To a 15 ml extraction tube, 250 ml of serum sample, 100 ml of 0.5 M NaH 2 PO 4 , 750 ml of distilled water and 4 ml of ethyl acetate was added. The tube was shaken for 10 min and centrifuged at 3000 rpm for 10 min. The ethyl acetate extracts were separated by freezing the water phase for 5 min, followed by decanting the organic phase into a clean glass tube. To this water phase, 4 ml of ethyl acetate was added and the ethyl acetate extraction was performed again. Each ethyl acetate extract was combined and evaporated to dryness. The residue was dissolved in 100 ml of the mobile phase. Twenty
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five ml of this fraction was injected into the HPLC system. The same HPLC apparatus for 5-ASA analysis was used for FT analysis. The analytical column was maintained at 558C for all separations. The composition of the mobile phase 1 and 2 was a mixture of acetonitrile and deionized water (10:90, v / v); the pH was adjusted at 3.0 with trifluoroacetic acid. The flow-rates of the pumps P1 and P2 were 0.8 and 0.5 ml min 21 , respectively. Both column switching times (T1 and T2) were set to 0.5 min. FT eluted from the analytical column was detected by UV absorption monitored at 270 nm. The concentrations of FT in the serum samples were determined from the calibration curve. The mean extraction efficiency of FT from plasma was 90.5%. The standard curve of FT added to the dog serum was linear over the range of 0-2.0 mg ml 21 and passed through the origin.
4.3. Plasma CBZ concentration To a 15 ml extraction tube, 200 ml of plasma sample, 8 ml of methylene chloride, 1 ml of ethyl acetate and 0.067 M phosphate buffer (pH 6.0) were added. The tube was shaken for 10 min and centrifuged at 3000 rpm for 10 min. After removing the aqueous phase, the organic phase was evaporated to dryness. The residue was dissolved in 200 ml of the mobile phase. Eighty ml of this fraction was injected into the HPLC system. The same HPLC apparatus for 5-ASA analysis but without column switching equipment was used for the CBZ analysis. The column was maintained at 558C for separation. The composition of the mobile phase was as follows: deionized water:acetonitrile:tetrahydrofuran (70:26:4, v / v). The flow-rate was 1.0 ml min 21 . CBZ eluted from the analytical column was detected by UV absorption monitored at 285 nm. The concentrations of CBZ in the plasma samples were determined from the calibration curve. The standard curve of CBZ added to the dog plasma was linear over the range of 0–1.0 mg ml 21 and passed through the origin.
5. Pharmacokinetic analysis The following pharmacokinetic parameters were
determined from the plasma or serum drug concentration-time data. Cmax was the maximum drug concentration and T max was the time taken to reach Cmax . The area under the plasma or serum drug concentration vs. time curve (AUC) and the area under the first-moment curve (AUMC) after i.v. and / or oral administrations were calculated using the linear trapezoidal rule up to the last measured plasma or serum drug concentration. The mean residence time (MRT) after oral administration was calculated by AUMC /AUC. The extent of bioavailability (BA) was calculated from the Dose i.v ., Dose oral , AUCi.v. and AUCoral by the following equation, BA5 AUCoral ?Dose i.v. /AUCi.v.?Dose oral .
6. Statistics All values are expressed as their mean6S.E. Statistical differences were assumed to be reproducible when P,0.05 (one-sided t-test).
7. Results
7.1. In vitro dissolution tests Dissolution tests were performed on the eight preparations listed in Table 1, where 5-ASA was used as a representative hydrophilic drug, and FT and CBZ were chosen as representative hydrophobic drugs. Results are shown in Figs. 1–3. Fig. 1 presents the results of 5-ASA dissolution studies. As the release of drug from the PCC needs the physical disintegration of the capsule, dissolution study was performed after small debris was made on PCC. The dissolution of 5-ASA from PCC was very fast and was completed within 2 min. However, the dissolution of 5-ASA from tablets made by a compression force of 20 kg cm 22 was delayed as compared to PCC. At 2 min, after the beginning of dissolution tests, only about 90% of 5-ASA was released; almost 4 min was required for complete release. When the tablet compression force was high, i.e., 100 kg cm 22 , the dissolution rate of 5-ASA from the tablet was further delayed. Half the amount of 5-ASA was released at 2 min and it took 10 min for 5-ASA to be released completely. In the case of FT where the
T. Takaya et al. / Journal of Controlled Release 50 (1998) 111 – 122
Fig. 1. Comparison of the release profiles of 5-ASA from PCC and tablets. j: 5-ASA suspension in PCC, d: 5-ASA tablet (compression force520 kg cm 22 ), m: 5-ASA tablet (compression force5100 kg cm 22 ). Each point represents the mean6S.E. (n5 3).
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same kinds of preparations (tablets and PCC) were used, almost the same results were obtained as with 5-ASA (Fig. 2). The release of FT from PCC was completed within 2 min. However, the release of FT from tablets (compression force520 kg cm 22 ) finished only at 6 min after the start of dissolution tests. Furthermore, the dissolution of FT from the tablets (compression force5100 kg cm 22 ) were not completed even at 20 min. In CBZ studies, similar results were obtained (Fig. 3). The dissolution of CBZ from TCCs containing a CBZ suspension with Witepsol was completed within 6 min. However, the release of CBZ from TCCs containing a physical mixture of CBZ and lactose was not completed within 20 min. Dissolution rate of CBZ from the drug container varied, which was ascribed to the state of drug in the container (i.e., whether the drug molecules were in the solid state or in suspension / solution).
7.2. Oral administration studies in beagle dogs
Fig. 2. Comparison of the release profiles of FT from PCC and tablets. j: FT solution in PCC, d: FT tablet (compression force520 kg cm 22 ), m: FT tablet (compression force5100 kg cm 22 ). Each point represents the mean6S.E. (n53).
Fig. 3. Comparison of the release profiles of CBZ from drug container of TCC. j: CBZ suspension with Witepsol, d: physical mixture of CBZ and lactose. Each point represents the mean6S.E. (n53).
Fig. 4 shows the plasma 5-ASA concentrationtime curves after oral administration of two kinds of 5-ASA preparations. 5-ASA tablet prepared by the compression force with 100 kg cm 22 was used for this in vivo study, as the tablet with 20 kg cm 22 compression force was fragile. In the case of Eudragit S coated tablets, 5-ASA started to appear in the systemic circulation at 2 h after administration and
Fig. 4. Plasma 5-ASA concentration-time curves after oral administration of two kinds of 5-ASA preparations to beagle dogs, 25 mg / kg. The broken lines represent the plasma 5-ASA concentration-time curves of three dogs after oral administration of 5-ASA Eudragit S preparation. The solid lines represent the plasma 5-ASA concentration-time curves of three dogs after administration of PCC containing 5-ASA solution with PG.
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the mean T max was 3.0 h, where the mean Cmax was 21 5.5261.70 mg ml . On the other hand, in the case of 5-ASA in PCCs, the mean T max was 5.360.9 h 21 and Cmax was 16.8961.74 mg ml . The mean colon arrival time of PCCs in fasted beagle dogs was reported to be about 3.3 h in our previous paper [15]. Since 5-ASA was detected in dog plasma from 4 h after administration, it was suggested that 5-ASA was delivered to the colon by the PCC system, and that the PCC disintegrated and released the 5-ASA suspension there. The intra individual variation of plasma 5-ASA levels in the Eudragit S coated tablet group was larger than that in the PCC group. The pharmacokinetic parameters of 5-ASA are listed in Table 2. The T max of Eudragit S coated tablets was shorter than that of PCCs by 2.3 h. On the other hand, the Cmax of 5-ASA from PCCs was about three fold higher than that from Eudragit S coated tablets, and the AUC values of 5-ASA from PCCs was about two fold higher than that of Eudragit S coated tablets. The same studies were performed with the second model drug, FT, at a dose of 1 mg / kg. Fig. 5 shows the serum FT concentration-time curves after the administration of two kinds of FT preparations. According to the same reason in the case of 5-ASA, FT tablet prepared with 100 kg cm 22 compression force was used for this study. FT started to appear in the serum at 2 h after administration of FT Eudragit S coated tablets and serum FT concentrations increased gradually 7 h where it reached its Cmax . The mean Cmax was 0.8760.21 mg ml 21 . Next, PCCs containing FT dissolved in a PEG mixture were
Fig. 5. Serum FT concentration-time curves after i.v. (0.25 mg / kg) or oral (1 mg / kg) administrations of two kinds of FT preparations to beagle dogs. The dotted lines represent the serum FT concentration-time curves of three dogs after i.v. administration of FT solution. The broken lines represent the serum FT concentration-time curves of three dogs after oral administration of FT Eudragit S preparation. The solid lines represent the serum FT concentration-time curves of three dogs after oral administration of PCC containing FT and PEG as base.
administered to beagle dogs. PEG was selected as a base because it changed to a liquid state after oral administration to dogs (i.e., at body temperature). In this experiment, FT was detected at 3–6 h after administration and FT concentration increased rapidly as compared with Eudragit S coated tablets. The mean T max was 6.6760.88 h and the Cmax was 1.4660.22 mg ml 21 . The i.v. injection of FT was performed in the same dogs in order to estimate the systemic availability of FT. These results are also
Table 2 Pharmacokinetic parameter values obtained after oral administration of 5-ASA to beagle dogs, 25mg / kg Test
Pharmacokinetic parameter
preparation
Cmax (mg / ml)
Eudragit S coated tablet PCC
T max (h)
AUC (mg?h / ml)
MRT (h)
5.5261.70
3.060.0
22.5766.15
4.5160.22
16.8961.74
5.360.9
48.0969.3 8
6.2260.34
Cmax : maximum plasma drug concentration. T max : the time when the plasma drug concentration reaches to its maximum concentration. AUC: area under the plasma drug concentration vs. time curve. MRT : mean residence time. Each point represents the mean6S.E. (n53). *: Statistically significant difference (P,0.05).
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Table 3 Pharmacokinetic parameter values obtained after i.v. and oral administrations of FT to beagle dogs Test
Pharmacokinetic parameter
preparation
Dose (mg / kg)
Cmax (mg / ml)
T max (h)
i.v. solution Eudragit S coated tablet PCC
0.25
0.7360.03
0.0
5.5560.69
8.1660.32
1.0
0.8760.21
7.060.6
9.7361.73
10.5960.22
43.7967.80
1.0
1.4660.22
6.760.9
15.5560.25
11.3460.78
70.8460.35
AUC (mg?h / ml)
MRT (h)
BA (%) 100
BA: extent of bioavailability. Each value represents the mean6S.E. (n53). *: Statistically significant difference (P,0.05).
shown in Fig. 5. The pharmacokinetic parameter values of FT are shown in Table 3. There was no significant difference in the T max and Cmax between the two preparations. However, there was a signifi-
Fig. 6. Plasma CBZ concentration-time curves after oral administration of two kinds of CBZ preparations to beagle dogs, 5 mg / kg. The broken lines represent the plasma CBZ concentration-time curves of three dogs after oral administration of FT Eudragit S preparation. The solid lines represent the plasma CBZ concentration-time curves of three dogs after administration of TCC containing a suspension of CBZ with Witepsol.
cant difference in the AUC values between these preparations. The BA value of FT from Eudragit S coated tablets was 43.7967.80% and that from PCC was 70.8460.35%. There was a significant difference between these two BA values. Finally, the systemic availability of CBZ was investigated where another system, namely TCC, was used. In this study, CBZ was filled into the drug container capsule of TCC in two forms. One form consisted of a physical mixture of CBZ and lactose in a solid state. The second form was a suspension of CBZ with Witepsol. Fig. 6 shows the results of these studies and pharmacokinetic parameter values are listed in Table 4. In both preparations, CBZ appeared in the systemic circulation at 3–4 h after administration, and the mean T maxs were 4.360.3 and 4.760.3 h, respectively. There was no significant difference between the two preparations. The mean Cmaxs were 0.2260.02 and 0.3760.05 mg ml 21 , respectively. The Cmax of the suspension was significantly higher than Cmax of solid preparation. AUC values were 0.39260.058 and 0.67360.019 mg?h ml 21 , respectively.
Table 4 Pharmacokinetic parameter values obtained after oral admiration of CBZ to beagle dogs, 5mg / kg Test
Pharmacokinetic parameter
preparation
Cmax (mg / ml)
T max (h)
AUC (mg?h / ml)
MRT (h)
Physical mixture Witepsol suspension
0.2260.021 0.3760.05
4.360.3 4.760.3
0.39260.058 0.67360.019
4.6060.32 4.6060.42
Each value represents the mean6S.E. (n53). *: Statistically significant difference (P,0.05).
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8. Discussion In this paper, in vitro dissolution tests and in vivo pharmacokinetic studies were performed on solid and liquid preparations in colon delivery systems using three model drugs representing both hydrophilic and hydrophobic compounds. The correlation between the release rate of drugs from the colon delivery systems and the systemic availability of drugs from the colon was studied. Colon delivery systems have been the focus of much attention recently because they are thought to be effective devices for oral dosing of peptide / protein drugs. In addition, they allow for optimal delivery of drugs designed to act on the colonic lumen, such as drugs for inflammatory bowel disease. Since a report concerning the use of azo-polymer for colon delivery system by Saffran in 1986 [1], many investigators have been engaged in developing colon delivery systems [2–12]. Recently, we have developed two kind of colon delivery capsules, namely PCC and TCC and reported their applications to a representative protein drug, rhGCSF [13], drugs for inflammatory bowel disease, 5-ASA [15] and fluorescein [13,16]. The characteristics of PCC are as follows: (1) PCC is made of EC, which has been used as pharmaceutical adjuvant for a long time, and therefore its safety is well established. (2) PCC can contain drug in solution or suspension in suppository base. (3) Drug release occurs instantaneously by physical destruction in the colon due to inner pressure. (4) Drug release from PCC is independent of pH in the gastrointestinal tract. (5) Drug release is independent of the gastrointestinal transit time. (6) PCC is prepared easily. On the other hand, TCC has some characteristics as follows. (1) TCC is also made of EC. (2) TCC can contain drug powder or drug in suppository base. (3) Drug release from TCC is dependent on the time, i.e., TCC releases drug at predetermined time. Initially, 5-ASA was used as a hydrophilic model drug. As 5-ASA is rapidly absorbed from the small intestine after oral administration, SASP, its prodrug, has been used in clinical stages over 50 years [21]. However, some 5-ASA preparations, such as Olsalazine [22] and Asacol [19], have been developed to overcome the side effects of SASP. Asacol is a 5-ASA tablet which is coated with Eudragit S [19].
The Eudragit S coated tablet used in this experiment is similar to Asacol. As Eudragit S dissolves at a pH greater than 7 [19], Eudragit S coated tablets releases drug at the lower small intestine [23]. Instead of Asacol, two types of Eudragit S coated 5-ASA tablets were prepared in this laboratory. As the compression force used for preparing Asacol was not uncertain, two conditions were tried. As expected, the tablet prepared with low compression force was dissolved faster than that with high compression force. The hardness study suggested that the tablet with compression force of 100 kg cm 22 is conceivable. Therefore, the systemic availability of 5-ASA was compared between tablet and PCC. As shown in Fig. 4, the time for the first appearance of 5-ASA into the systemic circulation from Eudragit S coated tablets was shorter than that from PCCs by 2.3 h. Our previous report showed that mean colon arrival time was 3.3 h in our beagle dogs in the fasted condition [13,14]. On the other hand, it was reported that the pH in the canine small intestine was higher than that of the human [24]. Therefore, the release of 5-ASA from Eudragit S coated tablets was thought to begin in the lower small intestine. On the other hand, PCC was thought to release 5-ASA in the colon. With respect to the Cmax and AUC values, there were significant differences between the two formulations. In the case of Eudragit S coated tablets, solid materials such as stools in the colon decreased both the amount and time of 5-ASA molecules coming in contact with the gut wall. In addition, 5-ASA molecules were not well dissolved by the gastrointestinal fluid because a solid dosage form was used. Therefore, Cmax and AUC values tended to show greater variations. However, since PCCs were filled with 5-ASA in solution, 5-ASA contact with the colonic mucosa occurred easily and 5-ASA was well absorbed there. The same experiment was performed using FT, as a hydrophobic model drug. FT is a derivative of 5-fluorouracil and has been used widely in patients suffering from colorectal cancer. In this study, a PEG mixture was used as a base for the PCCs, as it has been often used as a suppository base. The PEG mixture used in this study is solid at room temperature but becomes liquid after administration when it reaches body temperature. As FT is contained in the
T. Takaya et al. / Journal of Controlled Release 50 (1998) 111 – 122
PCC as solution, the dissolution rate of FT from the PCC was faster than that obtained from the tablet. The PCC containing FT disintegrates at colonic inner pressures as does these containing 5-ASA in PG solution. Therefore, PCC in which PEG was used as a base was favorable from the standpoint of both reservation and handling. In FT studies, similar properties were observed as in 5-ASA studies. However, although the absorption lag-times after the oral administration of the preparations were the same for 5-ASA and FT using Eudragit S coated tablets, the T max of FT after administration of Eudragit S coated tablets was delayed as compared to that of 5-ASA. This is thought to be due to the difference in the ratio of drug to pharmaceutical additive (i.e., crystalline cellulose) in the preparation. In the case of the FT preparation, since the drug ratio was about 3.8% of the total weight, it is thought that the crystalline cellulose bound strongly and the tablet did not easily disintegrate in the lower gastrointestinal tract. On the other hand, the systemic availability of FT delivered by PCCs was higher than that delivered by Eudragit S coated tablet. Since FT dissolved completely within the PEG mixture base, a good systemic availability of FT was obtained from the colon. With respect to the most hydrophobic model drug in this study, CBZ, the physical mixture of CBZ and lactose and the suspension of CBZ with Witepsol were introduced into the drug container of the TCC. As oily base was used to prepare TCC containing CBZ, the dissolution rate of CBZ from TCC was slow as compared to that observed in PCCs containing 5-ASA and / or FT. However, the in vivo systemic availability study using beagle dogs showed that TCC had higher systemic availability than tablet. It has been reported that the length-normalized intestinal permeability for CBZ administered in solution was greater in the colon than in the duodenojejunum by using a single pass perfusion technique [25]. However, CBZ absorption was reported to decrease when an Oros TM osmotic pump was located in the human colon [26]. As shown in Fig. 6, CBZ absorption was significantly increased by administering it as suspension using Witepsol. It is thought that the drug release rate from the drug container was improved by using the Witepsol
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suspension system, and a higher systemic availability was obtained.
9. Conclusions Colon delivery capsules such as PCC containing 5-ASA as suspension, PCC containing FT as solution and TCC containing CBZ as oily solution, showed 2.13, 1.60 and 1.72 times higher systemic availability of each drug than that obtained with Eudragit S coated tablets. In vitro dissolution study showed that the drug release from the colon delivery capsules were faster than that obtained from tablets. There was a correlation between the in vitro dissolution rate of drugs from the colon delivery systems and the in vivo systemic availability of drugs after oral administration to beagle dogs. Therefore, the importance of the dissolution process on the systemic availability of drugs having different physicochemical characteristics, 5-ASA, FT and CBZ, after oral administration to beagle dogs by colon delivery systems has been revealed.
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