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Preparation of highly porous gastroretentive metformin tablets using a sublimation method
Accepted Manuscript Research Paper Preparation and In Vivo Evaluation of Highly Porous Gastroretentive Metfor‐ min Tablets using a Sublimation method Tack-Oon Oh, Ju-Young Kim, Jung-Myung Ha, Sang-Cheol Chi, Yun-Seok Rhee, Chun-Woong Park, Eun-Seok Park PII: DOI: Reference:
S0939-6411(12)00375-X http://dx.doi.org/10.1016/j.ejpb.2012.11.009 EJPB 11262
To appear in:
European Journal of Pharmaceutics and Biopharma‐ ceutics
Received Date: Accepted Date:
25 July 2012 20 November 2012
Please cite this article as: T-O. Oh, J-Y. Kim, J-M. Ha, S-C. Chi, Y-S. Rhee, C-W. Park, E-S. Park, Preparation and In Vivo Evaluation of Highly Porous Gastroretentive Metformin Tablets using a Sublimation method, European Journal of Pharmaceutics and Biopharmaceutics (2012), doi: http://dx.doi.org/10.1016/j.ejpb.2012.11.009
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1
Preparation and In Vivo Evaluation of Highly Porous Gastroretentive Metformin Tablets using a Sublimation method
2 3 4 5 6 7
Tack-Oon Oh1, Ju-Young Kim1, Jung-Myung Ha1, Sang-Cheol Chi1, Yun-Seok Rhee2, ChunWoong Park3*, Eun-Seok Park1**
8 9 10
1
11 12
2
13
3
School of Pharmacy, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, Republic of Korea College of Pharmacy and Research Institute of Pharmaceutical Sciences, Gyeongsang National University, Jinju, Gyeongnam 660-751, Republic of Korea College of Pharmacy Chungbuk National University,
14 15 *
Co-correspondence to:
**
Correspondence to:
Chun-Woong Park, Ph.D.
Eun-Seok Park, Ph.D.
Assistant Professor,
Professor,
College of Pharmacy,
School of Pharmacy,
Chungbuk National University,
Sungkyunkwan University,
410 Seongbong-ro,
300 Cheoncheon-dong, Jangan-gu,
Cheongju, Chungbuk 361-763
Suwon, Gyeonggi-do 440-746
Republic of Korea
Republic of Korea
Tel: 82-43-261-2806
Tel: 82-31-290-7715 Fax: 82-31-290-7729
e-mail: [email protected] 16
e-mail: [email protected]
17 18
Abstract
19 20
The present investigation is aimed to formulate floating gastroretentive tablets containing
21
metformin using a sublimation material. In this study, the release of the drug from a matrix
22
tablet was highly dependent on the polymer concentrations. In all formulations, initial rapid
23
drug release was observed, possibly due to the properties of the drug and polymer. The effect
24
of the amount of PEO on swelling and eroding of the tablets was determined. The water
25
uptake and erosion behavior of the gastroretentive (GR) tablets was highly dependent on the
26
amount of PEO. The water uptake increased with increasing PEO concentration in the tablet
27
matrix. The weight loss from tablets decreased with increasing amounts of PEO. Camphor
28
was used as the sublimation material to prepare GR tablets that are low-density and easily
29
floatable. Camphor was changed to pores in the tablet during the sublimation process. SEM
30
revealed that the GR tablets have a highly porous morphology. Floating properties of tablets
31
and tablet density was affected by the sublimation of camphor. Prepared floating
32
gastroretentive tablets floated for over 24 h and had no floating lag time. However, as the
33
amount of camphor in the tablet matrix increased, the crushing strength of the tablet
34
decreased after sublimation. Release profiles of the drug from the GR tablets were not
35
affected by tablet density or porosity. In pharmacokinetic studies, the mean plasma
36
concentration of the GR tablets after oral administration was greater than the concentration of
37
glucophase XR. Also, the mean AUC0-∞ values for the GR tablets were significantly greater
38
than the plasma concentrations of glucophase XR.
39 40
Key words : Gastroretentive, Metformin, Floating tablet, Sublimation, Highly porous
41 42
1. Introduction
43 44
Oral administration is the most common route for drug delivery. The bioavailability of a
45
drug via oral administration can be affected by many factors such as the dosage form, the
46
drug release profile, gastric emptying, the gastrointestinal transit time and the site of drug
47
absorption. Several drugs are unstable in the acidic environment of the stomach and have a
48
narrow absorption window in the upper small intestine.
49
Metformin, a disubstituted biguanide, is an orally administered hypoglycemic agent [1].
50
Due to its ability to lower blood-glucose levels, it is widely used to treat type 2 diabetes.
51
Metformin is freely soluble in water and its absolute bioavailability is 50 to 60 %. The
52
absorption site for metformin is the proximal part of the small intestine where the
53
gastrointestinal absorption is complete after 6 h [2, 3]. To increase the bioavailability of
54
metformin, several approaches for controlled release and gastro-retentive dosage forms have
55
been reported [4-6].
56
Gastroretentive systems have some advantages over other methods of drug administration,
57
including a longer residence time in the stomach and local action to the narrow absorption
58
site in the upper small intestine [7]. Various methodological approaches for gastric retention
59
have been reported in the literature, such as muco-adhesive systems, floating systems,
60
sedimentation systems, biodegradable superporous hydrogel systems and expendable systems
61
[8]. The floating systems are floatable dosage forms that have a long-lasting intragastric
62
buoyancy. This system offers a sustained action to the therapeutic window and better patient
63
compliance [9]. Several technical methods have been used to prepare gastro-retentive floating
64
dosage forms. Hwang et al. [8] prepared the hydrodynamically balanced system (HBS) based
65
on hydrophilic polymers. The surface of the hydrophilic polymer of the formulation becomes
66
swollen and hydrated when it comes in contact with the gastric fluid, and then is floated.
67
Several researchers have investigated gas-generating systems [10-12]. These systems were
68
formulated with carbonate or bicarbonate, citric acid and some polymers. In the single unit
69
dosage forms, carbonates or bicarbonates react with acid such as citric acid or gastric fluid,
70
generating CO2 gas bubbles. The dosage forms are floated when the generated gas bubbles
71
are trapped in the swollen polymer matrix of the dosage forms. However, this system has
72
some problems. For example, the pH of the gastric fluid differs in each subject and is affected
73
by food. Furthermore, gas-generating dosage forms have a lag time until floating occurs.
74
Compared to gas-generating systems, low-density systems were immediately buoyant and not
75
affected by pH differences in the gastric fluid. Kawashima et al. [13] prepared low-density
76
hollow microspheres using solvent evaporation methods. Streubel et al. [14] prepared low-
77
density floating matrix tablets using low-density materials such as polypropylene form
78
powder.
79
Camphor, a sublimation material, is a crystalline ketone obtained from the East Asian
80
camphor tree (Cinnamonum camphora) [15]. K.-i. Koizumi et al. [16] prepare the rapidly
81
soluble compressed tablet using a sublimation method. Above the sublimation temperature,
82
camphor can be sublimated into the tablet matrix, producing pores in the matrix.
83
The objective of the present study was to develop a porous floating matrix tablet using the
84
sublimation method, as well as to evaluate the in vitro drug release and in vivo performance
85
of the released drug from the gastroretentive tablet.
86 87 88
2. Materials and methods
89 90
2.1. Materials
91 92
Metformin was donated by Pharmhispania S. A. Pharmaceuticals (Barcelona, Spain).
93
Phenformin was purchased from Sigma (St. Louis, MO, USA). Poly ethylene oxide (PEO)
94
(grade WSR 301) was donated by Colorcon Asia Pacipic Pte. Ltd. (Merchant Square,
95
Singapore). D,L-Camphor was purchased from Junsei chemical Co. Ltd. (Tokyo, Japan).
96
Hydroxypropyl cellulose (Klucel® LF) was purchased from Hercules Inc. (Wilmington, DE,
97
USA). Magnesium stearate was purchased from Acros organics (Belgium, USA). All other
98
ingredients, reagents and solvents were of analytical grade.
99 100
2.2. Methods
101 102
2.2.1. Preparation of GR tablets of metformin
103 104
Tablets were prepared by the conventional wet granulation method. Table 1 lists the
105
composition of different trial formulations prepared using various amounts of PEO WSR
106
301 as the release-controlling polymer, camphor as the sublimation material, fixed
107
quantities of Klucel® LF as the binder, and magnesium stearate as the lubricant. Metformin
108
was blended with Klucel® LF. The powders were then granulated with ethanol, sized using
109
a mesh (500 μm) and dried at 60 °C for approximately 2 h until a residual moisture content
110
of 1 to 2 % w/w remained. Ethanol was used for wet granulation to minimize dissolution of
111
metformin into water as metformin is freely soluble in water and slightly soluble in alcohol.
112
The dried granules were sized by a mesh (710 μm), mixed with different ratios of PEO
113
WSR 301 and camphor, lubricated with magnesium stearate and then compressed into
114
caplet-sized tablets on a hydraulic presser. The compression force was adjusted to make
115
hardness of the tablet to be 150 N. The width and length of produced tablet was 13 mm ×
116
8 mm and height was maintained between 6 mm and 8 mm. Manufactured tablets were
117
sublimated in 60 °C vacuum oven, and the weight of the tablets were measured at regular
118
time points. Tablets with final weight equal to theoretical weight after complete
119
sublimation (Table 1) were selected for further experiment. In this study, camphor was
120
completely sublimated within 24 hours.
121 122
2.2.2. Dissolution study
123 124
The release of metformin from the GR tablets was studied using the USP dissolution
125
apparatus II (Rotating paddle). The dissolution test was performed using 900 ml of 0.1 N
126
hydrochloric acid. The temperature was maintained at 37±0.5 °C. The rotation speed was 75
127
rpm. Five milliliters was withdrawn at predetermined time intervals of 0.25, 0.5, 0.75, 1, 2, 4,
128
6, 8 and 12 h. The medium was replenished with 5 ml of fresh dissolution medium each time.
129
The samples were filtered through a 0.45 μm membrane and diluted to a suitable
130
concentration with 0.1 N hydrochloric acid. Samples were analyzed by using UV/visible
131
spectroscopy at 232 nm. The percentage of drug release was plotted against time to determine
132
the release profiles.
133 134
2.2.3. Swelling or water uptake studies
135 136
The swelling property of the formulation was determined by various techniques [17, 18].
137
The water-uptake study of the tablet was carried out using USP dissolution apparatus II. The
138
medium employed was 0.1 N hydrochloric acid, 900 ml rotated at 75 rpm. The medium was
139
maintained at 37±0.5 °C throughout the study. After 1, 2, 4, 6, 8 and 12 h, the tablet was
140
withdrawn, blotted to remove excess water and weighed. The percentage increase in weight
141
due to absorbed liquid or water-uptake was estimated at each time point using the following
142
equation (1):
143
144
Weight change % =
Weight of the swollen tablet - initial weight of the tablet × 100 initial weight of the tablet
(1)
145 146
2.2.4. Matrix erosion studies
147 148
Matrix erosion studies were performed by a method similar to those of Roy and Rohera
149
[19]. In the erosion study, heating method instead of freeze drying was used for drying of
150
samples due to its convenience. Furthermore, all components into the sample were generally
151
known as stable materials during the condition of heating method. After the swelling studies,
152
the wet samples were then dried in an oven at 50 °C for 48 h, allowed to cool to room
153
temperature and finally weighed until constant weight was achieved (final dry weight). The
154
tablet erosion (ES) at different times was estimated using the following equation (2):
155
156
ES % =
initial weight of the tablet - weight of the dried tablet × 100 initial weight of the tablet
(2)
157 158
The percentage of the tablet remaining after erosion was calculated using the following
159
equation (3):
160 161
Remaining (%) = 100 – ES
162 163 164
2.2.5. In vitro buoyancy studies
(3)
165
The in vitro buoyancy was determined using the modified method described by Rosa et al
166
[20]. The tablets were placed in a 100 ml Nessler tube containing 0.1 N hydrochloric acid.
167
The time required for the tablets to rise to the surface and float was defined as the floating lag
168
time, and the total time the tablets stayed afloat was defined as total floating time.
169 170
2.2.6. Evaluation of GR tablet properties
171 172
For evaluation of physical properties of the tablet, tablets were prepared as described in
173
Section 2.2.1. using flat-faced die and punch with diameter of 13 mm instead. Three tablets
174
from each formulation were randomly selected, and the physical properties before and after
175
sublimation were evaluated. The crushing strength, or hardness, of the tablets was measured
176
with the help of Dr. Schleuniger Pharmatron’s hardness tester (Manchester, NH, USA) and
177
are expressed in newton (N).
178 179
The density of the GR tablets (g y cm-3) was calculated from the tablet height, diameter and mass using the following equation (4):
D = W / [(𝑀/2)2 × π × h]
180 181 182 183
where W is the mass of a tablet, M is the tablet diameter,
184
is the tablet height.
(4)
π is the circular constant, and h
185
The effect of the sublimation material (camphor) on the morphology of the GR tablets
186
was examined using a scanning electron microscope (SEM). Samples were coated with a thin
187
layer of palladium gold alloy in a Hummer I Sputter Coater, and imaged in a SEM (JSM-
188
7600F, JEOL, Tokyo, Japan).
189
190
2.2.7. Release kinetics
191 192 193
To study the release kinetics of metformin from the GR tablets, the release data were fitted to the following equations:
194 195
Zero-order equation [21] :
196
Qt = k0 · t
197 198 199
where Qt is the percentage of drug released at time t and k0 is the release rate constant;
200 201 202
First-order equation [22] :
203 204
ln (100 - Qt ) = ln100 - k1 · t
205 206
where k1 is the release rate constant.
207 208 209
The Higuchi’s equation [23] :
210 211
Qt = kH · t1/2
212 213
where kH is the Higuchi release rate constant.
214 215 216
The Hixson-Crowell equation [24] :
217
(100 - Qt )1/3 = 1001/3 - kHC · t
218 219 220
where kHc is the Hixson-Crowell rate constant.
221 222 223
Furthermore, to characterize the drug release mechanisms for the polymeric systems studied, the Korsmeyer-Peppas [25] model was applied:
224
Qt = kkp · tn Q∞
225 226 227
where Qt/Q∞ is the fraction of drug released at time t, kKP is a constant comprising the
228
structural and geometric characteristics of the device, and n is the release exponent, which is
229
indicative of the mechanism of drug release. For the case of cylindrical geometries such as
230
tablets, n=0.45 corresponds to a Fickian diffusion release (case I), 0.45
231
Fickian (anomalous) transport, n = 0.89 to a zero-order (case II) release kinetics [26] and
232
n>0.89 to a super case II transport [27]. Only data points in the 10 %-70 % interval were used
233
in fitting analysis.
234 235 236
2.2.8. LC-MS-MS conditions
237
Mass spectrometry was carried out on a Shimadzu prominence HPLC system. Nanospace
238
SI-2 3133 auto-injector (Shiseido Co, Ltd, Tokyo, Japan) and nanospace SI-2 3101 binary
239
pump (Shiseido Co, Ltd, Tokyo, Japan) were used for sample delivery.
240
The chromatographic separations were achieved on a Capcellpak CR50 column (100 mm
241
× 2.0 mm, 5 µm, Shiseido Co, Ltd, Japan). The mobile phase consisted of acetonitrile
242
containing 0.1 % formic acid /10 mM ammonium acetate containing 0.1 % formic acid
243
(60:40, v/v) at a flow rate of 0.2 ml/min.
244
Electrospray ionization with positive mode was used for the detection of metformin and
245
the internal standard (phenformin). The drying temperature was set to 350 °C. The voltage of
246
the ion spray was maintained at 5000 V. The nebulizer gas was set to 10 psi. Multiple reaction
247
monitoring (MRM) was used for detecting analytes and the collision energy was 29 V for
248
metformin and 31 V for phenformin. The transition of m/z 130.2-74.2 for metformin and m/z
249
206.2-60.2 for the internal standard were monitored at a dwell time of 200 ms per transition.
250 251
2.2.9. Sample preparation
252 253
The metformin standard stock solution was prepared by dissolving accurately weighed
254
material in methanol to give a final concentration of 1000 µg/ml. The working solutions in
255
the desired concentration range were prepared by dilution of the standard stock solution with
256
acetonitrile/water (50:50 v/v). An internal standard working solution was prepared by
257
dissolving accurately weighed phenformin in methanol and then diluted with 50 %
258
acetonitrile to a final concentration of 4.0 µg/ml.
259 260
The standard working solutions were used to spike blank plasma (180 µl) for preparation of standard curves and quality control samples. The calibration standard solutions were
261
prepared at concentration of 0.05, 0.1, 0.5, 1.0, 4.0, 10.0 and 40.0 µg/ml. Quality controls
262
were established at 0.50, 5.00 and 32.00 µg/ml. Spiked plasma samples were stored at -20 °C
263
before use.
264
For analysis, all frozen samples were allowed to equilibrate to room temperature. The
265
samples were vortexed to homogeneity. Additionally, 20 µl of an internal standard (4.0 µg/ml
266
of phenformin) and 600 µl of acetonitrile were added to a 200 µl aliquot of plasma. The
267
sample mixture was vortexed for 60 s and centrifuged at 13000 rpm for 5 min to precipitate
268
the protein, and 150 µl of clear supernatant was injected directly into the LC/MS/MS.
269 270
2.2.10. Pharmacokinetics studies
271 272
The in vivo works have been carried out in accordance with The EC Directive
273
86/609/EEC for animal experiments. Three female mini pigs (weighing approximately 12-16
274
kg) were used in this study. The animals were housed under 12 h light and 12 h darkness at
275
22±2 °C. The mini pigs were fed and had free access to water. For the PK study, the mini
276
pigs fasted overnight. Some food was given to the mini pigs approximately 6 h after dosing.
277
The drug was orally administered to the mini pigs using a standard balling gun. Three
278
mini pigs received the gastroretentive tablet formulation containing 500 mg of metformin and
279
three mini pigs received a commercial tablet product (Glucophage XR 500 mg).
280
For pharmacokinetic analysis, blood samples (10 ml) were drawn from the jugular vein at
281
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 h. Plasma samples were collected from the blood
282
(centrifugation at 3000 rpm for 10 min) and frozen at -40 °C until assayed .
283 284
285
3. Results
286 287
3.1. Effect of amount of PEO on in vitro release of metformin
288 289
The effect of different amounts of PEO on the in vitro release of metformin is shown in
290
Fig. 1. All formulations showed sustained drug release patterns. The duration of the extended
291
release varied depending on the amount of PEO. The dissolution rates of metformin from the
292
GR tablet were compared in terms of T50, the time at which 50% of the loading dose was
293
released. The T50 values of formulations A1, A2, A3, A4 and A5 were 1.3 h, 1.5 h, 1.9 h, 2.4 h
294
and 2.7 h, respectively. As the amount of PEO increased from 145 mg (A1) to 445 mg (A5)
295
per tablet, and from 18 % (A1) to 40 % (A5) in w/w percentage, the initial drug release, as
296
well as drug release in the later hours, decreased. Formulation A5, containing 445 mg of PEO
297
showed sustained release for over 12 h, while that containing less than 345 mg of PEO
298
completed the release within approximately 12 h.
299 300
3.2. Effect of amount of PEO on swelling properties of GR tablets
301 302
The effect of the amount of PEO on the swelling of GR tablets could be determined by
303
the water-uptake of the tablet. The percentage of water-uptake by the tablet was determined
304
by the method described in section 2.2.3 at different time intervals. The percentage of water-
305
uptake of the GR tablets prepared by varying the amount of PEO from 145 mg to 445 mg is
306
shown in Fig. 2. It was observed that the percentage of water-uptake of all formulations
307
gradually increased until reaching equilibrium and then gradually decreased. The water-
308
uptake was highly dependent on the amount of PEO. The percentage of water-uptake
309
increased with the amount of PEO in the tablet. As the amount of PEO increased, GR tablets
310
swelled rapidly, and the time to reach maximum water-uptake was delayed. The maximum
311
percentage of water-uptake of formulations A1, A2, A3, A4 and A5 were approximately 59 %,
312
78 %, 113 %, 146 % and 195 %, respectively.
313 314
3.3. Effect of amount of PEO on eroding properties of GR tablets
315 316
The time-dependent erosion behavior of the GR tablets is shown in Fig. 3. The percentage
317
of the matrices remaining reflects the amount of polymer dissolved and the erosion of the
318
matrix in media during the dissolution process. Weight loss from the tablets increased
319
progressively with time. Similar to the swelling data, the erosion of the GR tablets was
320
dependent on the amount of PEO. As the amount of PEO increased, the weight loss from
321
tablets decreased. Formulation A5, containing 445 mg of PEO, showed about 40 % of the
322
tablet mass remained after 12 h. However, the percentage of tablet mass remaining for
323
formulation A1, containing 145 mg of PEO, was only approximately 10 % after 12 h.
324 325
3.4. Effect of sublimation of camphor on tablet properties
326 327
The influence of the sublimation of camphor and its amount on the tablet properties was
328
investigated. The floating properties of the GR tablets and effects of sublimation on thickness,
329
density and crushing strength of the tablets are summarized in table 2. The crushing strength
330
of the tablets decreased after sublimation. Also, as camphor content in the tablet decreased
331
from 12.5% (A1) to 0% w/w (A10), the crushing strength of the GR tablet increased. The
332
density of tablets decreased after sublimation as well. The densities of the GR tablets
333
prepared from formulations A5, A6, A7, A8, A9, and A10 were 0.911, 0.926, 0.975, 0.980,
334
1.003, and 1.039 g/cm3, respectively. As camphor content decreased with fixed amount of
335
other excipients, the density of GR tablets increased. However, there was no tendency in
336
density of tablets with change in total tablet weight when camphor amount was fixed (A1 to
337
A5). When more than 40 mg of camphor was added to the GR tablet formulations, the density
338
of the tablets was less than 1.00 g/cm3. In all formulations, the thickness of tablets showed
339
slight increase after sublimation. Fig. 4 shows the floating property of the GR tablets having
340
different densities. Low-density tablet formulations containing more than 40 mg of camphor
341
(A5, A6, A7, and A8) have no floating lag time and floated for over 24 h, while formulations
342
containing less than 20 mg of camphor did not float.
343 344
3.5. Effect of amount of camphor on in vitro release of metformin
345 346
The effect of the amount of camphor on the release of the drug from the GR tablets is
347
shown in Fig. 5. There were no significant differences among drug release profiles of the
348
formulations. Increased amounts of sublimation material such as camphor lead to a decreased
349
density of the GR tablets after sublimation. Compared to the A5, A6, A7 and A8, tablets of
350
A9 and A10 have the higher densities than 1 g/cm3, which did not float in the dissolution
351
medium. However, dissolution profiles of the drug from tablets were not affected by the
352
amount of camphor. Regardless of floating properties, tablets containing the same amount of
353
drug and polymer show similar drug release profiles.
354 355
3.6. Release kinetics
356 357
The drug release data for all formulations were fitted to the zero-order, first-order,
358
Higuchi, Hixson-Crowell and Korsemeyer-Peppas models. Table 3 shows the values for the
359
correlation coefficient (R2), kinetic rate constant (k) and release exponent (n). The correlation
360
coefficient was used to determine the kinetic model best fit. None of the formulations fit the
361
zero-order kinetics model. The values of R2 calculated from the first-order, Higuchi and
362
Hixon-Crowell models suggested that all of the formulations behaved similarly to each other.
363
The n values for formulation A1 and A2 are 0.3779 and 0.4060 respectively, while the other
364
formulations have n values between 0.45 and 0.89.
365 366
3.7. SEM
367 368
Fig. 6 shows the morphology of a A5 before (Fig. 6a) / after (Fig. 6b) the sublimation of
369
camphor as viewed by SEM. Fig. 6a shows a dense and non-porous structure of the tablet
370
composites before the sublimation. The morphology of the tablet composites after
371
sublimation is highly porous (Fig. 6b). The pore sizes in the tablet were on the order of
372
several hundred micrometers in diameter. The density and floating property of the tablets
373
were affected by the presence of these pores.
374 375
3.8. Pharmacokinetics studies
376 377
Mean plasma concentration-time profiles of the drug are shown in Fig. 7. The mean
378
plasma concentrations after oral administration of the metformin GR tablets increased at
379
broader peaks than the plasma concentrations of the reference tablets. The mean
380
pharmacokinetic parameters are presented in Table 4. The mean Cmax values for the GR
381
tablets were 2765.69 ng/ml compared with 2156.59 ng/ml for the reference drugs. The mean
382
Tmax values for the GR tablets and reference drugs were 3.00 and 5.00 h, respectively.
383
However, the Cmax and Tmax values were not significantly different (P=0.05). Ke values for
384
the GR and reference tablets were 0.45 and 1.35 h-1, respectively. The T1/2 value for the GR
385
tablets was 1.55 h, whereas the T1/2 value for the reference drug was 0.52 h. The mean AUC0-
386
∞
387
(p<0.05).
value for the GR tablets were significantly greater than those for the reference drugs
388 389 390
4. Discussion
391 392
We have investigated floating gastroretentive tablets containing metformin. GR tablets
393
were prepared with various concentrations of hydrophilic polymer such as PEO and
394
sublimation material such as camphor. The GR tablets prepared by a sublimation process
395
presented the following properties: (i) the structure of GR tablet composite was highly porous,
396
(ii) the tablets had a low density and floated on the media with no floating lag time, (iii) the
397
floating duration of the GR tablets was more than 24 h, and (iv) the release rate of the drug
398
can be controlled by various concentrations of hydrophilic polymers.
399
In this study, the release of the drug from the matrix tablet was highly dependent on the
400
amount of polymer. Ford et al. [28, 29] and Velasco [30] investigated drug release from
401
hydrophilic polymer matrices such as HPMC with different drug to polymer ratios. As the
402
concentration of the polymer increased, the viscosity of the gel increased and a gel layer with
403
a longer diffusional path formed, decreasing the effective diffusion coefficient of the drug and
404
thus reducing the drug release rate.
405
In all formulations, initial rapid drug release was observed, possibly due to the properties
406
of the drug and polymer. The process of drug release from a hydrogel matrix tablet can be
407
divided into four steps: water penetrating into the hydrogel matrix tablet, dissolution of the
408
drug, diffusion of the drug through the matrix, and polymeric excipient erosion. The gel layer
409
requires time to control the drug release rate effectively. However, since rapid dissolution of
410
highly water-soluble drugs occurs when water penetrates into a matrix tablet, dissolution of
411
the drug is not a rate-limiting step in the release process. In vitro drug release from HPMC
412
matrix tablets composed of very soluble drugs was followed by drug diffusion, whereas
413
poorly soluble drug release was followed by erosion of polymeric excipients [30, 31].
414
Several researchers have reported swelling and erosion mechanisms of hydrophilic
415
polymers [32-34]. In the case of dry polymer matrices or non-swollen polymers, the chains of
416
polymer were entangled and had limited mobility. When polymer matrices come into contact
417
with water, the water diffuses into the polymer matrices. The water imbibition causes an
418
increase in the mobility of polymer chains, allowing entangled chains to adopt disentangled
419
configurations. As the polymer swells, the outer surface of the polymer contact with water is
420
dissolved and eroded. Fig 2 and Fig 3 shows that the swelling and erosion properties of the
421
GR tablets are dependent on the amount of polymer. Similar to high molecular weight
422
polymers, high amounts of polymer might form a more viscous gel layer, which causes a
423
decrease in the erosion of polymer matrices. Furthermore, because high molecular weight
424
polymers seal pores before allowing more liquid to enter, the polymer swells faster [32].
425
In this study, camphor was used as the sublimation material to prepare low-density, easily
426
floatable GR tablets. The floating properties of tablets depended on the tablet density, which
427
was affected by the sublimation of camphor. As camphor was sublimed, holes remained in the
428
tablet, giving the tablet a low-density, porous structure. The increase of tablet thickness after
429
camphor sublimation might be due to swelling of tablet caused by phase transition of
430
camphor from solid to gas. The density of the GR tablets depended on the amount of
431
camphor they contained before sublimation. Increasing the amount of camphor increased the
432
number of pores in the tablet and decreased the density of the tablets. There was no tendency
433
in density change of GR tablets total tablet weight alteration with fixed camphor amount (A1
434
to A5). And the reason is assumed to be the increase in thickness of the tablet as well as
435
increase of total tablet weight. The crushing strength was evaluated for GR tablets with
436
varying amounts of camphor. The decrease in crushing strength with increasing amounts of
437
camphor may be the result of the porous structure of the GR tablet after camphor sublimation.
438
In this study, the camphor particles used for preparing GR tablets were 60 mesh size (250
439
µm). However, the size of camphor size may affect the physical properties of tablets after
440
sublimation. With increasing size of camphor particles before sublimation causes larger inner
441
pore size of GR tablet increase after sublimation, and cause crushing strength of GR tablet to
442
decrease. On contrary, tablets with smaller particle size of camphor will have smaller inner
443
pore size, which has greater crushing strength than those prepared with bigger camphor
444
particles. However, too small camphor particles could cause nonhomogeneous mixing due to
445
their low flowability. As shown in Fig 5, release profiles of the drug from the GR tablets were
446
not affected by tablet density or porosity, suggesting that drug release from the tablets was
447
controlled by the properties of the polymer, such as its hydrophilicity, hydrophobicity,
448
molecular weight, and viscosity.
449
The results of release kinetics analyses of the drug from the GR tablets are shown in
450
Table 3. In general, Fickian diffusion was used to describe the release of the drug from the
451
matrix tablets. However, in the case of swelling polymers, release kinetics of the drug did not
452
follow Fickian diffusion because the polymer swells and changes volume [35]. In order to
453
describe drug release from swelling polymers, Korsmeyer and Peppas equation [25] called
454
the power law, was applied. This equation correlates two mechanisms of drug transport that
455
seem independent, Fickian diffusion and a case-II transport, thereby describing the release of
456
a drug from a swelling polymer. When n is 0.45, drug release is diffusion-controlled; when n
457
is 0.89, drug release is swelling-controlled. When n is between 0.45 and 0.89, release can be
458
defined as a combination of both phenomena [26]. Table 3 shows the values of n and all of
459
the correlation coefficients for each formulation. With some exceptional formulations, almost
460
all formulations have n values ranging from 0.45 to 0.89, which indicate anomalous transport.
461
In the current study, the in vivo pharmacokinetic behaviors of GR tablets containing
462
metformin and a commercial metformin sustained-release tablet product were compared. In
463
vitro study showed no difference GR tablet (A5) in dissolution profile with commercial tablet
464
product. However GR tablet (A5) had higher AUC0-∞ values than the commercial product,
465
which is assumed to be gastric retention effect of GR tablet. An initial fast release of the drug
466
from the GR tablets was observed during the first 3 h. This rapid initial drug release may be
467
due to the fact that some tablets were broken by gastric motility. The standard errors in AUC0-
468
∞
469
These variations are caused by gastric emptying or extended gastric transit [36].
for the metformin GR tablets were comparable to those for the commercial tablet product.
470 471 472
5. Conclusion
473 474
In the present study, floating gastroretentive tablets were successfully prepared using the
475
sublimation material camphor. Floating gastroretentive tablets have no floating lag time and
476
floated for over 24 h. However, hardness of the GR tablets decreased after camphor
477
sublimation. The drug release from the GR tablets was controlled by the hydrophilic swelling
478
of the polymer PEO. The mechanism employed for drug release from the GR tablets was
479
diffusion combined with erosion. Oral administration of the drug in mini pigs showed, an
480
enhanced bioavailability from the GR tablets compared to a commercial tablet product.
481 482 483 484
Acknowledgement
485 486 487
This study was supported by a grant of the Korean Health Technology R&D Project, Ministry for Health, Welfare & Family Affairs, Republic of Korea. (A092018)
488 489
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490
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release of diclofenac sodium from HPMC tablets, J. Controlled Release, 57 (1999) 75-85.
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Pharm., 18 (1992) 1355-1375.
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[32] L.S.C. Wan, P.W.S. Heng, L.F. Wong, The effect of hydroxypropylmethylcellulose on water
565
penetration into a matrix system, Int. J. Pharm., 73 (1991) 111-116.
566
[33] F. Veiga, T. Salsa, M.E. Pina, Oral Controlled Release Dosage Forms. II. Glassy Polymers in
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Hydrophilic Matrices, Drug Dev. Ind. Pharm., 24 (1998) 1-9.
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[35] M.D. Chavanpatil, P. Jain, S. Chaudhari, R. Shear, P.R. Vavia, Novel sustained release,
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[36] A.J. Coupe, S.S. Davis, D.F. Evans, I.R. Wilding, Correlation of the Gastric Emptying of
575
Nondisintegrating Tablets with Gastrointestinal Motility, Pharm. Res., 8 (1991) 1281-1285.
576 577
LIST OF FIGURES
578 579 580
Fig. 1. Effect of the PEO concentration on in vitro drug release from gastroretentive tablets of
581
metformin.
582
Fig. 2. Effect of the PEO concentration on water uptake of metformin gastroretentive tablets.
583
Fig. 3. Effect of the PEO concentration on erosion of metformin gastroretentive tablets.
584
Fig. 4. Effect of amount of the camphor on floating ability of tablets.
585
Fig. 5. Effect of amount of the camphor on in vitro drug release from gastroretentive tablets of
586
metformin.
587
Fig. 6. SEM pictures of cross-sections of tablets.
588
Fig. 7. Mean plasma concentration of metformin in mini pigs after oral administration of reference
589
drug (Glucophage XR) and GR tablet (A5).
590
120
Drug release(%)
100
80 A1 A2 A3 A4 A5 Glucophage XR
60
40
20
0 0
591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609
2
4
6
8
10
12
Time(h) Fig. 1. Effect of the PEO concentration on in vitro drug release from gastroretentive tablets of metformin. Bars represent mean±S.D (n=3).
610
300
Water uptake(%)
250
200
A1 A2 A3 A4 A5
150
100
50
0 0
611 612 613 614
2
4
6
8
10
12
Time(h) Fig. 2. Effect of the PEO concentration on water uptake of metformin gastroretentive tablets. Bars represent mean±S.D (n=3).
615
100
Remaining of tablets(%)
80
60
A1 A2 A3 A4 A5
40
20
0 0
616 617 618 619
2
4
6
8
10
12
Time(h) Fig. 3. Effect of the PEO concentration on erosion of metformin gastroretentive tablets. Bars represent mean±S.D (n=3).
620
621 622 623
624 625 626
627 628 629
630 631 632 633 634
Fig. 4. Effect of amount of the camphor on floating ability of tablets.
635
120
Drug release(%)
100
80 A5 A6 A7 A8 A9 A10
60
40
20
0 0
636 637 638 639
2
4
6
8
10
12
Time(h) Fig. 5. Effect of amount of the camphor on in vitro drug release from gastroretentive tablets of metformin. Bars represent mean±S.D (n=3).
640
641 642
(a)
643
644 645 646 647 648 649 650 651 652
(b) Fig. 6. SEM pictures of cross-sections of tablets. (a) tablets before the sublimation; (b) gastroretentive tablets after sublimation of camphor.
653
4000
Plasma concentration(ng/ml)
Glucophage XR A5
3000
2000
1000
0 0 654 655 656 657 658 659 660
2
4
6
8
10
12
Time(h) Fig. 7. Mean plasma concentration of metformin in mini pigs after oral administration of reference drug (Glucophage XR) and GR tablet (A5). Bars represent mean±S.E (n=3).
661
LIST OF TABLES
662 663
Table 1. The composition, in milligrams, of the designed GR tablets containing metformin
664
Table 2. Characterization of gastroretentive tablets of metformin
665
Table 3. Kinetic parameters of metformin gastroretentive tablet formulations
666
Table 4. Pharmacokinetic parameters of reference drug (Glucophage XR) and gastroretentive tablet
667
(A5) after oral administration to mini pigs at dose of 500mg
668 669 670
Table 1. The composition, in milligrams, of the designed GR tablets containing metformin Formulation code
671
a
(mg)
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
Metformin
500
500
500
500
500
500
500
500
500
500
Hydroxypropyl cellulose
30
30
30
30
30
30
30
30
30
30
Polyethylene oxide
145
200
245
345
445
445
445
445
445
445
Camphor
100
100
100
100
100
80
60
40
20
-
Magnesium stearate
25
25
25
25
25
25
25
25
25
25
Total (Before sublimation)
800
855
900
1000
1100
1080
1060
1040
1020
1000
Totala (After sublimation)
700
755
800
900
1000
1000
1000
1000
1000
1000
Theoretical weight of tablet after complete sublimation of camphor
672 673 674
Table 2. Characterization of GR tablets of metformin Before sublimation Formulation code
675 676
After sublimation
Thickness (mm)
Density (g/cm3)
Crushing Strength (N)
Thickness (mm)
Density (g/cm3)
Crushing Strength (N)
Floating lag time (min)
Duration of floating (h)
A1
5.407±0.049
1.107±0.009
140.7±2.5
5.623±0.068
0.926±0.018
70.7±4.2
0
>24
A2
5.807±0.031
1.101±0.004
149.0±1.0
6.103±0.032
0.906±0.009
76.0±6.6
0
>24
A3
6.097±0.049
1.101±0.008
152.3±1.2
6.480±0.036
0.911±0.009
85.3±3.1
0
>24
A4
6.920±0.056
1.075±0.007
155.7±4.0
7.450±0.044
0.886±0.006
98.3±10.0
0
>24
A5
7.920±0.017
1.038±0.002
150.7±14.2
8.473±0.035
0.911±0.006
83.7±2.5
0
>24
A6
7.613±0.025
1.064±0.001
158.3±14.0
8.190±0.056
0.926±0.009
98.3±6.1
0
>24
A7
7.603±0.045
1.042±0.005
145.3±2.1
8.177±0.055
0.975±0.005
86.7±1.2
0
>24
A8
7.297±0.051
1.060±0.015
146.3±1.2
7.883±0.087
0.980±0.019
111.3±15.5
0
>24
A9
7.197±0.071
1.058±0.013
157.3±8.4
7.643±0.085
1.003±0.015
125.0±14.5
N.F.a
N.F.a
A10
7.017±0.125
1.067±0.020
165.0±6.2
7.493±0.031
1.039±0.005
138.7±11.9
N.F.a
N.F.a
Mean (±S.D) of 3 tablets a N.F. : Not floating
677 678 679
680 681
Table 3. Kinetic parameters of metformin GR tablet formulations Zero order
First order
Higuchi
Hixson & crow
Korsmeyer & Peppas
Formulation code
R2
K
R2
K
R2
K
R2
K
R2
n
K
A1
0.8305
6.3307
0.9978
0.1466
0.9506
26.499
0.9744
0.2700
0.9832
0.3779
43.521
A2
0.8513
6.4636
0.9871
0.1326
0.9620
26.884
0.9823
0.2568
0.9832
0.4060
40.050
A3
0.8831
7.1916
0.8897
0.2028
0.9777
29.606
0.9941
0.3111
0.9887
0.4812
34.041
A4
0.9198
7.3251
0.9209
0.1445
0.9924
29.768
0.9281
0.3625
0.9910
0.5243
29.655
A5
0.9059
6.6327
0.9978
0.0834
0.9871
27.088
0.9839
0.2009
0.9898
0.4991
29.174
A6
0.9369
6.8781
0.9885
0.0907
0.9961
27.747
0.9956
0.2131
0.9966
0.5155
27.530
A7
0.9506
6.6520
0.9718
0.1058
0.9979
27.863
0.9982
0.2283
0.9993
0.4875
29.404
A8
0.9357
6.8386
0.9925
0.0889
0.9960
27.604
0.9954
0.2105
0.9966
0.5104
27.810
A9
0.9287
6.8420
0.9983
0.0883
0.9929
27.679
0.9917
0.2102
0.9975
0.4989
28.615
A10
0.8905
6.3428
0.9920
0.0745
0.9812
26.049
0.9686
0.1853
0.9848
0.4850
29.813
2
R =coefficient of determination K=slope
682 683 684 685
686 687
Table 4. Pharmacokinetic parameters of reference drug (Glucophage XR) and GR tablet (A5) after oral administration to mini pigs at dose of 500mg (Mean±S.E.). Ke (h-1)
AUC0-∞ (ng h/ml)
T1/2 (h)
Cmax (ng/ml)
Tmax (h)
Reference drug (Glucophage XR)
1.35±0.23
18041.79±443.86
0.52±0.09
2156.59±80.70
5.00±1.53
Gastro-retentive tablet (A5)
0.45±0.02*
21551.13±1433.16*
1.55±0.08*
2765.69±751.40
3.00±0.58
* p<0.05 when compared with reference drug using t-test.
S0939-6411(12)00375-X http://dx.doi.org/10.1016/j.ejpb.2012.11.009 EJPB 11262
To appear in:
European Journal of Pharmaceutics and Biopharma‐ ceutics
Received Date: Accepted Date:
25 July 2012 20 November 2012
Please cite this article as: T-O. Oh, J-Y. Kim, J-M. Ha, S-C. Chi, Y-S. Rhee, C-W. Park, E-S. Park, Preparation and In Vivo Evaluation of Highly Porous Gastroretentive Metformin Tablets using a Sublimation method, European Journal of Pharmaceutics and Biopharmaceutics (2012), doi: http://dx.doi.org/10.1016/j.ejpb.2012.11.009
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1
Preparation and In Vivo Evaluation of Highly Porous Gastroretentive Metformin Tablets using a Sublimation method
2 3 4 5 6 7
Tack-Oon Oh1, Ju-Young Kim1, Jung-Myung Ha1, Sang-Cheol Chi1, Yun-Seok Rhee2, ChunWoong Park3*, Eun-Seok Park1**
8 9 10
1
11 12
2
13
3
School of Pharmacy, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, Republic of Korea College of Pharmacy and Research Institute of Pharmaceutical Sciences, Gyeongsang National University, Jinju, Gyeongnam 660-751, Republic of Korea College of Pharmacy Chungbuk National University,
14 15 *
Co-correspondence to:
**
Correspondence to:
Chun-Woong Park, Ph.D.
Eun-Seok Park, Ph.D.
Assistant Professor,
Professor,
College of Pharmacy,
School of Pharmacy,
Chungbuk National University,
Sungkyunkwan University,
410 Seongbong-ro,
300 Cheoncheon-dong, Jangan-gu,
Cheongju, Chungbuk 361-763
Suwon, Gyeonggi-do 440-746
Republic of Korea
Republic of Korea
Tel: 82-43-261-2806
Tel: 82-31-290-7715 Fax: 82-31-290-7729
e-mail: [email protected] 16
e-mail: [email protected]
17 18
Abstract
19 20
The present investigation is aimed to formulate floating gastroretentive tablets containing
21
metformin using a sublimation material. In this study, the release of the drug from a matrix
22
tablet was highly dependent on the polymer concentrations. In all formulations, initial rapid
23
drug release was observed, possibly due to the properties of the drug and polymer. The effect
24
of the amount of PEO on swelling and eroding of the tablets was determined. The water
25
uptake and erosion behavior of the gastroretentive (GR) tablets was highly dependent on the
26
amount of PEO. The water uptake increased with increasing PEO concentration in the tablet
27
matrix. The weight loss from tablets decreased with increasing amounts of PEO. Camphor
28
was used as the sublimation material to prepare GR tablets that are low-density and easily
29
floatable. Camphor was changed to pores in the tablet during the sublimation process. SEM
30
revealed that the GR tablets have a highly porous morphology. Floating properties of tablets
31
and tablet density was affected by the sublimation of camphor. Prepared floating
32
gastroretentive tablets floated for over 24 h and had no floating lag time. However, as the
33
amount of camphor in the tablet matrix increased, the crushing strength of the tablet
34
decreased after sublimation. Release profiles of the drug from the GR tablets were not
35
affected by tablet density or porosity. In pharmacokinetic studies, the mean plasma
36
concentration of the GR tablets after oral administration was greater than the concentration of
37
glucophase XR. Also, the mean AUC0-∞ values for the GR tablets were significantly greater
38
than the plasma concentrations of glucophase XR.
39 40
Key words : Gastroretentive, Metformin, Floating tablet, Sublimation, Highly porous
41 42
1. Introduction
43 44
Oral administration is the most common route for drug delivery. The bioavailability of a
45
drug via oral administration can be affected by many factors such as the dosage form, the
46
drug release profile, gastric emptying, the gastrointestinal transit time and the site of drug
47
absorption. Several drugs are unstable in the acidic environment of the stomach and have a
48
narrow absorption window in the upper small intestine.
49
Metformin, a disubstituted biguanide, is an orally administered hypoglycemic agent [1].
50
Due to its ability to lower blood-glucose levels, it is widely used to treat type 2 diabetes.
51
Metformin is freely soluble in water and its absolute bioavailability is 50 to 60 %. The
52
absorption site for metformin is the proximal part of the small intestine where the
53
gastrointestinal absorption is complete after 6 h [2, 3]. To increase the bioavailability of
54
metformin, several approaches for controlled release and gastro-retentive dosage forms have
55
been reported [4-6].
56
Gastroretentive systems have some advantages over other methods of drug administration,
57
including a longer residence time in the stomach and local action to the narrow absorption
58
site in the upper small intestine [7]. Various methodological approaches for gastric retention
59
have been reported in the literature, such as muco-adhesive systems, floating systems,
60
sedimentation systems, biodegradable superporous hydrogel systems and expendable systems
61
[8]. The floating systems are floatable dosage forms that have a long-lasting intragastric
62
buoyancy. This system offers a sustained action to the therapeutic window and better patient
63
compliance [9]. Several technical methods have been used to prepare gastro-retentive floating
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dosage forms. Hwang et al. [8] prepared the hydrodynamically balanced system (HBS) based
65
on hydrophilic polymers. The surface of the hydrophilic polymer of the formulation becomes
66
swollen and hydrated when it comes in contact with the gastric fluid, and then is floated.
67
Several researchers have investigated gas-generating systems [10-12]. These systems were
68
formulated with carbonate or bicarbonate, citric acid and some polymers. In the single unit
69
dosage forms, carbonates or bicarbonates react with acid such as citric acid or gastric fluid,
70
generating CO2 gas bubbles. The dosage forms are floated when the generated gas bubbles
71
are trapped in the swollen polymer matrix of the dosage forms. However, this system has
72
some problems. For example, the pH of the gastric fluid differs in each subject and is affected
73
by food. Furthermore, gas-generating dosage forms have a lag time until floating occurs.
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Compared to gas-generating systems, low-density systems were immediately buoyant and not
75
affected by pH differences in the gastric fluid. Kawashima et al. [13] prepared low-density
76
hollow microspheres using solvent evaporation methods. Streubel et al. [14] prepared low-
77
density floating matrix tablets using low-density materials such as polypropylene form
78
powder.
79
Camphor, a sublimation material, is a crystalline ketone obtained from the East Asian
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camphor tree (Cinnamonum camphora) [15]. K.-i. Koizumi et al. [16] prepare the rapidly
81
soluble compressed tablet using a sublimation method. Above the sublimation temperature,
82
camphor can be sublimated into the tablet matrix, producing pores in the matrix.
83
The objective of the present study was to develop a porous floating matrix tablet using the
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sublimation method, as well as to evaluate the in vitro drug release and in vivo performance
85
of the released drug from the gastroretentive tablet.
86 87 88
2. Materials and methods
89 90
2.1. Materials
91 92
Metformin was donated by Pharmhispania S. A. Pharmaceuticals (Barcelona, Spain).
93
Phenformin was purchased from Sigma (St. Louis, MO, USA). Poly ethylene oxide (PEO)
94
(grade WSR 301) was donated by Colorcon Asia Pacipic Pte. Ltd. (Merchant Square,
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Singapore). D,L-Camphor was purchased from Junsei chemical Co. Ltd. (Tokyo, Japan).
96
Hydroxypropyl cellulose (Klucel® LF) was purchased from Hercules Inc. (Wilmington, DE,
97
USA). Magnesium stearate was purchased from Acros organics (Belgium, USA). All other
98
ingredients, reagents and solvents were of analytical grade.
99 100
2.2. Methods
101 102
2.2.1. Preparation of GR tablets of metformin
103 104
Tablets were prepared by the conventional wet granulation method. Table 1 lists the
105
composition of different trial formulations prepared using various amounts of PEO WSR
106
301 as the release-controlling polymer, camphor as the sublimation material, fixed
107
quantities of Klucel® LF as the binder, and magnesium stearate as the lubricant. Metformin
108
was blended with Klucel® LF. The powders were then granulated with ethanol, sized using
109
a mesh (500 μm) and dried at 60 °C for approximately 2 h until a residual moisture content
110
of 1 to 2 % w/w remained. Ethanol was used for wet granulation to minimize dissolution of
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metformin into water as metformin is freely soluble in water and slightly soluble in alcohol.
112
The dried granules were sized by a mesh (710 μm), mixed with different ratios of PEO
113
WSR 301 and camphor, lubricated with magnesium stearate and then compressed into
114
caplet-sized tablets on a hydraulic presser. The compression force was adjusted to make
115
hardness of the tablet to be 150 N. The width and length of produced tablet was 13 mm ×
116
8 mm and height was maintained between 6 mm and 8 mm. Manufactured tablets were
117
sublimated in 60 °C vacuum oven, and the weight of the tablets were measured at regular
118
time points. Tablets with final weight equal to theoretical weight after complete
119
sublimation (Table 1) were selected for further experiment. In this study, camphor was
120
completely sublimated within 24 hours.
121 122
2.2.2. Dissolution study
123 124
The release of metformin from the GR tablets was studied using the USP dissolution
125
apparatus II (Rotating paddle). The dissolution test was performed using 900 ml of 0.1 N
126
hydrochloric acid. The temperature was maintained at 37±0.5 °C. The rotation speed was 75
127
rpm. Five milliliters was withdrawn at predetermined time intervals of 0.25, 0.5, 0.75, 1, 2, 4,
128
6, 8 and 12 h. The medium was replenished with 5 ml of fresh dissolution medium each time.
129
The samples were filtered through a 0.45 μm membrane and diluted to a suitable
130
concentration with 0.1 N hydrochloric acid. Samples were analyzed by using UV/visible
131
spectroscopy at 232 nm. The percentage of drug release was plotted against time to determine
132
the release profiles.
133 134
2.2.3. Swelling or water uptake studies
135 136
The swelling property of the formulation was determined by various techniques [17, 18].
137
The water-uptake study of the tablet was carried out using USP dissolution apparatus II. The
138
medium employed was 0.1 N hydrochloric acid, 900 ml rotated at 75 rpm. The medium was
139
maintained at 37±0.5 °C throughout the study. After 1, 2, 4, 6, 8 and 12 h, the tablet was
140
withdrawn, blotted to remove excess water and weighed. The percentage increase in weight
141
due to absorbed liquid or water-uptake was estimated at each time point using the following
142
equation (1):
143
144
Weight change % =
Weight of the swollen tablet - initial weight of the tablet × 100 initial weight of the tablet
(1)
145 146
2.2.4. Matrix erosion studies
147 148
Matrix erosion studies were performed by a method similar to those of Roy and Rohera
149
[19]. In the erosion study, heating method instead of freeze drying was used for drying of
150
samples due to its convenience. Furthermore, all components into the sample were generally
151
known as stable materials during the condition of heating method. After the swelling studies,
152
the wet samples were then dried in an oven at 50 °C for 48 h, allowed to cool to room
153
temperature and finally weighed until constant weight was achieved (final dry weight). The
154
tablet erosion (ES) at different times was estimated using the following equation (2):
155
156
ES % =
initial weight of the tablet - weight of the dried tablet × 100 initial weight of the tablet
(2)
157 158
The percentage of the tablet remaining after erosion was calculated using the following
159
equation (3):
160 161
Remaining (%) = 100 – ES
162 163 164
2.2.5. In vitro buoyancy studies
(3)
165
The in vitro buoyancy was determined using the modified method described by Rosa et al
166
[20]. The tablets were placed in a 100 ml Nessler tube containing 0.1 N hydrochloric acid.
167
The time required for the tablets to rise to the surface and float was defined as the floating lag
168
time, and the total time the tablets stayed afloat was defined as total floating time.
169 170
2.2.6. Evaluation of GR tablet properties
171 172
For evaluation of physical properties of the tablet, tablets were prepared as described in
173
Section 2.2.1. using flat-faced die and punch with diameter of 13 mm instead. Three tablets
174
from each formulation were randomly selected, and the physical properties before and after
175
sublimation were evaluated. The crushing strength, or hardness, of the tablets was measured
176
with the help of Dr. Schleuniger Pharmatron’s hardness tester (Manchester, NH, USA) and
177
are expressed in newton (N).
178 179
The density of the GR tablets (g y cm-3) was calculated from the tablet height, diameter and mass using the following equation (4):
D = W / [(𝑀/2)2 × π × h]
180 181 182 183
where W is the mass of a tablet, M is the tablet diameter,
184
is the tablet height.
(4)
π is the circular constant, and h
185
The effect of the sublimation material (camphor) on the morphology of the GR tablets
186
was examined using a scanning electron microscope (SEM). Samples were coated with a thin
187
layer of palladium gold alloy in a Hummer I Sputter Coater, and imaged in a SEM (JSM-
188
7600F, JEOL, Tokyo, Japan).
189
190
2.2.7. Release kinetics
191 192 193
To study the release kinetics of metformin from the GR tablets, the release data were fitted to the following equations:
194 195
Zero-order equation [21] :
196
Qt = k0 · t
197 198 199
where Qt is the percentage of drug released at time t and k0 is the release rate constant;
200 201 202
First-order equation [22] :
203 204
ln (100 - Qt ) = ln100 - k1 · t
205 206
where k1 is the release rate constant.
207 208 209
The Higuchi’s equation [23] :
210 211
Qt = kH · t1/2
212 213
where kH is the Higuchi release rate constant.
214 215 216
The Hixson-Crowell equation [24] :
217
(100 - Qt )1/3 = 1001/3 - kHC · t
218 219 220
where kHc is the Hixson-Crowell rate constant.
221 222 223
Furthermore, to characterize the drug release mechanisms for the polymeric systems studied, the Korsmeyer-Peppas [25] model was applied:
224
Qt = kkp · tn Q∞
225 226 227
where Qt/Q∞ is the fraction of drug released at time t, kKP is a constant comprising the
228
structural and geometric characteristics of the device, and n is the release exponent, which is
229
indicative of the mechanism of drug release. For the case of cylindrical geometries such as
230
tablets, n=0.45 corresponds to a Fickian diffusion release (case I), 0.45
231
Fickian (anomalous) transport, n = 0.89 to a zero-order (case II) release kinetics [26] and
232
n>0.89 to a super case II transport [27]. Only data points in the 10 %-70 % interval were used
233
in fitting analysis.
234 235 236
2.2.8. LC-MS-MS conditions
237
Mass spectrometry was carried out on a Shimadzu prominence HPLC system. Nanospace
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SI-2 3133 auto-injector (Shiseido Co, Ltd, Tokyo, Japan) and nanospace SI-2 3101 binary
239
pump (Shiseido Co, Ltd, Tokyo, Japan) were used for sample delivery.
240
The chromatographic separations were achieved on a Capcellpak CR50 column (100 mm
241
× 2.0 mm, 5 µm, Shiseido Co, Ltd, Japan). The mobile phase consisted of acetonitrile
242
containing 0.1 % formic acid /10 mM ammonium acetate containing 0.1 % formic acid
243
(60:40, v/v) at a flow rate of 0.2 ml/min.
244
Electrospray ionization with positive mode was used for the detection of metformin and
245
the internal standard (phenformin). The drying temperature was set to 350 °C. The voltage of
246
the ion spray was maintained at 5000 V. The nebulizer gas was set to 10 psi. Multiple reaction
247
monitoring (MRM) was used for detecting analytes and the collision energy was 29 V for
248
metformin and 31 V for phenformin. The transition of m/z 130.2-74.2 for metformin and m/z
249
206.2-60.2 for the internal standard were monitored at a dwell time of 200 ms per transition.
250 251
2.2.9. Sample preparation
252 253
The metformin standard stock solution was prepared by dissolving accurately weighed
254
material in methanol to give a final concentration of 1000 µg/ml. The working solutions in
255
the desired concentration range were prepared by dilution of the standard stock solution with
256
acetonitrile/water (50:50 v/v). An internal standard working solution was prepared by
257
dissolving accurately weighed phenformin in methanol and then diluted with 50 %
258
acetonitrile to a final concentration of 4.0 µg/ml.
259 260
The standard working solutions were used to spike blank plasma (180 µl) for preparation of standard curves and quality control samples. The calibration standard solutions were
261
prepared at concentration of 0.05, 0.1, 0.5, 1.0, 4.0, 10.0 and 40.0 µg/ml. Quality controls
262
were established at 0.50, 5.00 and 32.00 µg/ml. Spiked plasma samples were stored at -20 °C
263
before use.
264
For analysis, all frozen samples were allowed to equilibrate to room temperature. The
265
samples were vortexed to homogeneity. Additionally, 20 µl of an internal standard (4.0 µg/ml
266
of phenformin) and 600 µl of acetonitrile were added to a 200 µl aliquot of plasma. The
267
sample mixture was vortexed for 60 s and centrifuged at 13000 rpm for 5 min to precipitate
268
the protein, and 150 µl of clear supernatant was injected directly into the LC/MS/MS.
269 270
2.2.10. Pharmacokinetics studies
271 272
The in vivo works have been carried out in accordance with The EC Directive
273
86/609/EEC for animal experiments. Three female mini pigs (weighing approximately 12-16
274
kg) were used in this study. The animals were housed under 12 h light and 12 h darkness at
275
22±2 °C. The mini pigs were fed and had free access to water. For the PK study, the mini
276
pigs fasted overnight. Some food was given to the mini pigs approximately 6 h after dosing.
277
The drug was orally administered to the mini pigs using a standard balling gun. Three
278
mini pigs received the gastroretentive tablet formulation containing 500 mg of metformin and
279
three mini pigs received a commercial tablet product (Glucophage XR 500 mg).
280
For pharmacokinetic analysis, blood samples (10 ml) were drawn from the jugular vein at
281
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 h. Plasma samples were collected from the blood
282
(centrifugation at 3000 rpm for 10 min) and frozen at -40 °C until assayed .
283 284
285
3. Results
286 287
3.1. Effect of amount of PEO on in vitro release of metformin
288 289
The effect of different amounts of PEO on the in vitro release of metformin is shown in
290
Fig. 1. All formulations showed sustained drug release patterns. The duration of the extended
291
release varied depending on the amount of PEO. The dissolution rates of metformin from the
292
GR tablet were compared in terms of T50, the time at which 50% of the loading dose was
293
released. The T50 values of formulations A1, A2, A3, A4 and A5 were 1.3 h, 1.5 h, 1.9 h, 2.4 h
294
and 2.7 h, respectively. As the amount of PEO increased from 145 mg (A1) to 445 mg (A5)
295
per tablet, and from 18 % (A1) to 40 % (A5) in w/w percentage, the initial drug release, as
296
well as drug release in the later hours, decreased. Formulation A5, containing 445 mg of PEO
297
showed sustained release for over 12 h, while that containing less than 345 mg of PEO
298
completed the release within approximately 12 h.
299 300
3.2. Effect of amount of PEO on swelling properties of GR tablets
301 302
The effect of the amount of PEO on the swelling of GR tablets could be determined by
303
the water-uptake of the tablet. The percentage of water-uptake by the tablet was determined
304
by the method described in section 2.2.3 at different time intervals. The percentage of water-
305
uptake of the GR tablets prepared by varying the amount of PEO from 145 mg to 445 mg is
306
shown in Fig. 2. It was observed that the percentage of water-uptake of all formulations
307
gradually increased until reaching equilibrium and then gradually decreased. The water-
308
uptake was highly dependent on the amount of PEO. The percentage of water-uptake
309
increased with the amount of PEO in the tablet. As the amount of PEO increased, GR tablets
310
swelled rapidly, and the time to reach maximum water-uptake was delayed. The maximum
311
percentage of water-uptake of formulations A1, A2, A3, A4 and A5 were approximately 59 %,
312
78 %, 113 %, 146 % and 195 %, respectively.
313 314
3.3. Effect of amount of PEO on eroding properties of GR tablets
315 316
The time-dependent erosion behavior of the GR tablets is shown in Fig. 3. The percentage
317
of the matrices remaining reflects the amount of polymer dissolved and the erosion of the
318
matrix in media during the dissolution process. Weight loss from the tablets increased
319
progressively with time. Similar to the swelling data, the erosion of the GR tablets was
320
dependent on the amount of PEO. As the amount of PEO increased, the weight loss from
321
tablets decreased. Formulation A5, containing 445 mg of PEO, showed about 40 % of the
322
tablet mass remained after 12 h. However, the percentage of tablet mass remaining for
323
formulation A1, containing 145 mg of PEO, was only approximately 10 % after 12 h.
324 325
3.4. Effect of sublimation of camphor on tablet properties
326 327
The influence of the sublimation of camphor and its amount on the tablet properties was
328
investigated. The floating properties of the GR tablets and effects of sublimation on thickness,
329
density and crushing strength of the tablets are summarized in table 2. The crushing strength
330
of the tablets decreased after sublimation. Also, as camphor content in the tablet decreased
331
from 12.5% (A1) to 0% w/w (A10), the crushing strength of the GR tablet increased. The
332
density of tablets decreased after sublimation as well. The densities of the GR tablets
333
prepared from formulations A5, A6, A7, A8, A9, and A10 were 0.911, 0.926, 0.975, 0.980,
334
1.003, and 1.039 g/cm3, respectively. As camphor content decreased with fixed amount of
335
other excipients, the density of GR tablets increased. However, there was no tendency in
336
density of tablets with change in total tablet weight when camphor amount was fixed (A1 to
337
A5). When more than 40 mg of camphor was added to the GR tablet formulations, the density
338
of the tablets was less than 1.00 g/cm3. In all formulations, the thickness of tablets showed
339
slight increase after sublimation. Fig. 4 shows the floating property of the GR tablets having
340
different densities. Low-density tablet formulations containing more than 40 mg of camphor
341
(A5, A6, A7, and A8) have no floating lag time and floated for over 24 h, while formulations
342
containing less than 20 mg of camphor did not float.
343 344
3.5. Effect of amount of camphor on in vitro release of metformin
345 346
The effect of the amount of camphor on the release of the drug from the GR tablets is
347
shown in Fig. 5. There were no significant differences among drug release profiles of the
348
formulations. Increased amounts of sublimation material such as camphor lead to a decreased
349
density of the GR tablets after sublimation. Compared to the A5, A6, A7 and A8, tablets of
350
A9 and A10 have the higher densities than 1 g/cm3, which did not float in the dissolution
351
medium. However, dissolution profiles of the drug from tablets were not affected by the
352
amount of camphor. Regardless of floating properties, tablets containing the same amount of
353
drug and polymer show similar drug release profiles.
354 355
3.6. Release kinetics
356 357
The drug release data for all formulations were fitted to the zero-order, first-order,
358
Higuchi, Hixson-Crowell and Korsemeyer-Peppas models. Table 3 shows the values for the
359
correlation coefficient (R2), kinetic rate constant (k) and release exponent (n). The correlation
360
coefficient was used to determine the kinetic model best fit. None of the formulations fit the
361
zero-order kinetics model. The values of R2 calculated from the first-order, Higuchi and
362
Hixon-Crowell models suggested that all of the formulations behaved similarly to each other.
363
The n values for formulation A1 and A2 are 0.3779 and 0.4060 respectively, while the other
364
formulations have n values between 0.45 and 0.89.
365 366
3.7. SEM
367 368
Fig. 6 shows the morphology of a A5 before (Fig. 6a) / after (Fig. 6b) the sublimation of
369
camphor as viewed by SEM. Fig. 6a shows a dense and non-porous structure of the tablet
370
composites before the sublimation. The morphology of the tablet composites after
371
sublimation is highly porous (Fig. 6b). The pore sizes in the tablet were on the order of
372
several hundred micrometers in diameter. The density and floating property of the tablets
373
were affected by the presence of these pores.
374 375
3.8. Pharmacokinetics studies
376 377
Mean plasma concentration-time profiles of the drug are shown in Fig. 7. The mean
378
plasma concentrations after oral administration of the metformin GR tablets increased at
379
broader peaks than the plasma concentrations of the reference tablets. The mean
380
pharmacokinetic parameters are presented in Table 4. The mean Cmax values for the GR
381
tablets were 2765.69 ng/ml compared with 2156.59 ng/ml for the reference drugs. The mean
382
Tmax values for the GR tablets and reference drugs were 3.00 and 5.00 h, respectively.
383
However, the Cmax and Tmax values were not significantly different (P=0.05). Ke values for
384
the GR and reference tablets were 0.45 and 1.35 h-1, respectively. The T1/2 value for the GR
385
tablets was 1.55 h, whereas the T1/2 value for the reference drug was 0.52 h. The mean AUC0-
386
∞
387
(p<0.05).
value for the GR tablets were significantly greater than those for the reference drugs
388 389 390
4. Discussion
391 392
We have investigated floating gastroretentive tablets containing metformin. GR tablets
393
were prepared with various concentrations of hydrophilic polymer such as PEO and
394
sublimation material such as camphor. The GR tablets prepared by a sublimation process
395
presented the following properties: (i) the structure of GR tablet composite was highly porous,
396
(ii) the tablets had a low density and floated on the media with no floating lag time, (iii) the
397
floating duration of the GR tablets was more than 24 h, and (iv) the release rate of the drug
398
can be controlled by various concentrations of hydrophilic polymers.
399
In this study, the release of the drug from the matrix tablet was highly dependent on the
400
amount of polymer. Ford et al. [28, 29] and Velasco [30] investigated drug release from
401
hydrophilic polymer matrices such as HPMC with different drug to polymer ratios. As the
402
concentration of the polymer increased, the viscosity of the gel increased and a gel layer with
403
a longer diffusional path formed, decreasing the effective diffusion coefficient of the drug and
404
thus reducing the drug release rate.
405
In all formulations, initial rapid drug release was observed, possibly due to the properties
406
of the drug and polymer. The process of drug release from a hydrogel matrix tablet can be
407
divided into four steps: water penetrating into the hydrogel matrix tablet, dissolution of the
408
drug, diffusion of the drug through the matrix, and polymeric excipient erosion. The gel layer
409
requires time to control the drug release rate effectively. However, since rapid dissolution of
410
highly water-soluble drugs occurs when water penetrates into a matrix tablet, dissolution of
411
the drug is not a rate-limiting step in the release process. In vitro drug release from HPMC
412
matrix tablets composed of very soluble drugs was followed by drug diffusion, whereas
413
poorly soluble drug release was followed by erosion of polymeric excipients [30, 31].
414
Several researchers have reported swelling and erosion mechanisms of hydrophilic
415
polymers [32-34]. In the case of dry polymer matrices or non-swollen polymers, the chains of
416
polymer were entangled and had limited mobility. When polymer matrices come into contact
417
with water, the water diffuses into the polymer matrices. The water imbibition causes an
418
increase in the mobility of polymer chains, allowing entangled chains to adopt disentangled
419
configurations. As the polymer swells, the outer surface of the polymer contact with water is
420
dissolved and eroded. Fig 2 and Fig 3 shows that the swelling and erosion properties of the
421
GR tablets are dependent on the amount of polymer. Similar to high molecular weight
422
polymers, high amounts of polymer might form a more viscous gel layer, which causes a
423
decrease in the erosion of polymer matrices. Furthermore, because high molecular weight
424
polymers seal pores before allowing more liquid to enter, the polymer swells faster [32].
425
In this study, camphor was used as the sublimation material to prepare low-density, easily
426
floatable GR tablets. The floating properties of tablets depended on the tablet density, which
427
was affected by the sublimation of camphor. As camphor was sublimed, holes remained in the
428
tablet, giving the tablet a low-density, porous structure. The increase of tablet thickness after
429
camphor sublimation might be due to swelling of tablet caused by phase transition of
430
camphor from solid to gas. The density of the GR tablets depended on the amount of
431
camphor they contained before sublimation. Increasing the amount of camphor increased the
432
number of pores in the tablet and decreased the density of the tablets. There was no tendency
433
in density change of GR tablets total tablet weight alteration with fixed camphor amount (A1
434
to A5). And the reason is assumed to be the increase in thickness of the tablet as well as
435
increase of total tablet weight. The crushing strength was evaluated for GR tablets with
436
varying amounts of camphor. The decrease in crushing strength with increasing amounts of
437
camphor may be the result of the porous structure of the GR tablet after camphor sublimation.
438
In this study, the camphor particles used for preparing GR tablets were 60 mesh size (250
439
µm). However, the size of camphor size may affect the physical properties of tablets after
440
sublimation. With increasing size of camphor particles before sublimation causes larger inner
441
pore size of GR tablet increase after sublimation, and cause crushing strength of GR tablet to
442
decrease. On contrary, tablets with smaller particle size of camphor will have smaller inner
443
pore size, which has greater crushing strength than those prepared with bigger camphor
444
particles. However, too small camphor particles could cause nonhomogeneous mixing due to
445
their low flowability. As shown in Fig 5, release profiles of the drug from the GR tablets were
446
not affected by tablet density or porosity, suggesting that drug release from the tablets was
447
controlled by the properties of the polymer, such as its hydrophilicity, hydrophobicity,
448
molecular weight, and viscosity.
449
The results of release kinetics analyses of the drug from the GR tablets are shown in
450
Table 3. In general, Fickian diffusion was used to describe the release of the drug from the
451
matrix tablets. However, in the case of swelling polymers, release kinetics of the drug did not
452
follow Fickian diffusion because the polymer swells and changes volume [35]. In order to
453
describe drug release from swelling polymers, Korsmeyer and Peppas equation [25] called
454
the power law, was applied. This equation correlates two mechanisms of drug transport that
455
seem independent, Fickian diffusion and a case-II transport, thereby describing the release of
456
a drug from a swelling polymer. When n is 0.45, drug release is diffusion-controlled; when n
457
is 0.89, drug release is swelling-controlled. When n is between 0.45 and 0.89, release can be
458
defined as a combination of both phenomena [26]. Table 3 shows the values of n and all of
459
the correlation coefficients for each formulation. With some exceptional formulations, almost
460
all formulations have n values ranging from 0.45 to 0.89, which indicate anomalous transport.
461
In the current study, the in vivo pharmacokinetic behaviors of GR tablets containing
462
metformin and a commercial metformin sustained-release tablet product were compared. In
463
vitro study showed no difference GR tablet (A5) in dissolution profile with commercial tablet
464
product. However GR tablet (A5) had higher AUC0-∞ values than the commercial product,
465
which is assumed to be gastric retention effect of GR tablet. An initial fast release of the drug
466
from the GR tablets was observed during the first 3 h. This rapid initial drug release may be
467
due to the fact that some tablets were broken by gastric motility. The standard errors in AUC0-
468
∞
469
These variations are caused by gastric emptying or extended gastric transit [36].
for the metformin GR tablets were comparable to those for the commercial tablet product.
470 471 472
5. Conclusion
473 474
In the present study, floating gastroretentive tablets were successfully prepared using the
475
sublimation material camphor. Floating gastroretentive tablets have no floating lag time and
476
floated for over 24 h. However, hardness of the GR tablets decreased after camphor
477
sublimation. The drug release from the GR tablets was controlled by the hydrophilic swelling
478
of the polymer PEO. The mechanism employed for drug release from the GR tablets was
479
diffusion combined with erosion. Oral administration of the drug in mini pigs showed, an
480
enhanced bioavailability from the GR tablets compared to a commercial tablet product.
481 482 483 484
Acknowledgement
485 486 487
This study was supported by a grant of the Korean Health Technology R&D Project, Ministry for Health, Welfare & Family Affairs, Republic of Korea. (A092018)
488 489
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490
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576 577
LIST OF FIGURES
578 579 580
Fig. 1. Effect of the PEO concentration on in vitro drug release from gastroretentive tablets of
581
metformin.
582
Fig. 2. Effect of the PEO concentration on water uptake of metformin gastroretentive tablets.
583
Fig. 3. Effect of the PEO concentration on erosion of metformin gastroretentive tablets.
584
Fig. 4. Effect of amount of the camphor on floating ability of tablets.
585
Fig. 5. Effect of amount of the camphor on in vitro drug release from gastroretentive tablets of
586
metformin.
587
Fig. 6. SEM pictures of cross-sections of tablets.
588
Fig. 7. Mean plasma concentration of metformin in mini pigs after oral administration of reference
589
drug (Glucophage XR) and GR tablet (A5).
590
120
Drug release(%)
100
80 A1 A2 A3 A4 A5 Glucophage XR
60
40
20
0 0
591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609
2
4
6
8
10
12
Time(h) Fig. 1. Effect of the PEO concentration on in vitro drug release from gastroretentive tablets of metformin. Bars represent mean±S.D (n=3).
610
300
Water uptake(%)
250
200
A1 A2 A3 A4 A5
150
100
50
0 0
611 612 613 614
2
4
6
8
10
12
Time(h) Fig. 2. Effect of the PEO concentration on water uptake of metformin gastroretentive tablets. Bars represent mean±S.D (n=3).
615
100
Remaining of tablets(%)
80
60
A1 A2 A3 A4 A5
40
20
0 0
616 617 618 619
2
4
6
8
10
12
Time(h) Fig. 3. Effect of the PEO concentration on erosion of metformin gastroretentive tablets. Bars represent mean±S.D (n=3).
620
621 622 623
624 625 626
627 628 629
630 631 632 633 634
Fig. 4. Effect of amount of the camphor on floating ability of tablets.
635
120
Drug release(%)
100
80 A5 A6 A7 A8 A9 A10
60
40
20
0 0
636 637 638 639
2
4
6
8
10
12
Time(h) Fig. 5. Effect of amount of the camphor on in vitro drug release from gastroretentive tablets of metformin. Bars represent mean±S.D (n=3).
640
641 642
(a)
643
644 645 646 647 648 649 650 651 652
(b) Fig. 6. SEM pictures of cross-sections of tablets. (a) tablets before the sublimation; (b) gastroretentive tablets after sublimation of camphor.
653
4000
Plasma concentration(ng/ml)
Glucophage XR A5
3000
2000
1000
0 0 654 655 656 657 658 659 660
2
4
6
8
10
12
Time(h) Fig. 7. Mean plasma concentration of metformin in mini pigs after oral administration of reference drug (Glucophage XR) and GR tablet (A5). Bars represent mean±S.E (n=3).
661
LIST OF TABLES
662 663
Table 1. The composition, in milligrams, of the designed GR tablets containing metformin
664
Table 2. Characterization of gastroretentive tablets of metformin
665
Table 3. Kinetic parameters of metformin gastroretentive tablet formulations
666
Table 4. Pharmacokinetic parameters of reference drug (Glucophage XR) and gastroretentive tablet
667
(A5) after oral administration to mini pigs at dose of 500mg
668 669 670
Table 1. The composition, in milligrams, of the designed GR tablets containing metformin Formulation code
671
a
(mg)
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
Metformin
500
500
500
500
500
500
500
500
500
500
Hydroxypropyl cellulose
30
30
30
30
30
30
30
30
30
30
Polyethylene oxide
145
200
245
345
445
445
445
445
445
445
Camphor
100
100
100
100
100
80
60
40
20
-
Magnesium stearate
25
25
25
25
25
25
25
25
25
25
Total (Before sublimation)
800
855
900
1000
1100
1080
1060
1040
1020
1000
Totala (After sublimation)
700
755
800
900
1000
1000
1000
1000
1000
1000
Theoretical weight of tablet after complete sublimation of camphor
672 673 674
Table 2. Characterization of GR tablets of metformin Before sublimation Formulation code
675 676
After sublimation
Thickness (mm)
Density (g/cm3)
Crushing Strength (N)
Thickness (mm)
Density (g/cm3)
Crushing Strength (N)
Floating lag time (min)
Duration of floating (h)
A1
5.407±0.049
1.107±0.009
140.7±2.5
5.623±0.068
0.926±0.018
70.7±4.2
0
>24
A2
5.807±0.031
1.101±0.004
149.0±1.0
6.103±0.032
0.906±0.009
76.0±6.6
0
>24
A3
6.097±0.049
1.101±0.008
152.3±1.2
6.480±0.036
0.911±0.009
85.3±3.1
0
>24
A4
6.920±0.056
1.075±0.007
155.7±4.0
7.450±0.044
0.886±0.006
98.3±10.0
0
>24
A5
7.920±0.017
1.038±0.002
150.7±14.2
8.473±0.035
0.911±0.006
83.7±2.5
0
>24
A6
7.613±0.025
1.064±0.001
158.3±14.0
8.190±0.056
0.926±0.009
98.3±6.1
0
>24
A7
7.603±0.045
1.042±0.005
145.3±2.1
8.177±0.055
0.975±0.005
86.7±1.2
0
>24
A8
7.297±0.051
1.060±0.015
146.3±1.2
7.883±0.087
0.980±0.019
111.3±15.5
0
>24
A9
7.197±0.071
1.058±0.013
157.3±8.4
7.643±0.085
1.003±0.015
125.0±14.5
N.F.a
N.F.a
A10
7.017±0.125
1.067±0.020
165.0±6.2
7.493±0.031
1.039±0.005
138.7±11.9
N.F.a
N.F.a
Mean (±S.D) of 3 tablets a N.F. : Not floating
677 678 679
680 681
Table 3. Kinetic parameters of metformin GR tablet formulations Zero order
First order
Higuchi
Hixson & crow
Korsmeyer & Peppas
Formulation code
R2
K
R2
K
R2
K
R2
K
R2
n
K
A1
0.8305
6.3307
0.9978
0.1466
0.9506
26.499
0.9744
0.2700
0.9832
0.3779
43.521
A2
0.8513
6.4636
0.9871
0.1326
0.9620
26.884
0.9823
0.2568
0.9832
0.4060
40.050
A3
0.8831
7.1916
0.8897
0.2028
0.9777
29.606
0.9941
0.3111
0.9887
0.4812
34.041
A4
0.9198
7.3251
0.9209
0.1445
0.9924
29.768
0.9281
0.3625
0.9910
0.5243
29.655
A5
0.9059
6.6327
0.9978
0.0834
0.9871
27.088
0.9839
0.2009
0.9898
0.4991
29.174
A6
0.9369
6.8781
0.9885
0.0907
0.9961
27.747
0.9956
0.2131
0.9966
0.5155
27.530
A7
0.9506
6.6520
0.9718
0.1058
0.9979
27.863
0.9982
0.2283
0.9993
0.4875
29.404
A8
0.9357
6.8386
0.9925
0.0889
0.9960
27.604
0.9954
0.2105
0.9966
0.5104
27.810
A9
0.9287
6.8420
0.9983
0.0883
0.9929
27.679
0.9917
0.2102
0.9975
0.4989
28.615
A10
0.8905
6.3428
0.9920
0.0745
0.9812
26.049
0.9686
0.1853
0.9848
0.4850
29.813
2
R =coefficient of determination K=slope
682 683 684 685
686 687
Table 4. Pharmacokinetic parameters of reference drug (Glucophage XR) and GR tablet (A5) after oral administration to mini pigs at dose of 500mg (Mean±S.E.). Ke (h-1)
AUC0-∞ (ng h/ml)
T1/2 (h)
Cmax (ng/ml)
Tmax (h)
Reference drug (Glucophage XR)
1.35±0.23
18041.79±443.86
0.52±0.09
2156.59±80.70
5.00±1.53
Gastro-retentive tablet (A5)
0.45±0.02*
21551.13±1433.16*
1.55±0.08*
2765.69±751.40
3.00±0.58
* p<0.05 when compared with reference drug using t-test.