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Solid lipid nanoparticles (SLN) for controlled drug delivery
Podium Presentations-Drug
Delivery II I Eur. J. Pharm.
If a hydrophilic drug is a substrate for a canter-mediated transport mechanism across the jejunal mucosa, it will largely influence its total transport rate. The effective intestinal permeability (Peff) value will be influenced by the substrate affinity and the total transport capacity. Estimates of Peff-values for transport across the human mucosa in the small intestinal are lacking, since few studies have been performed This is mainly due to a lack of a human clinical investigation tool. We have therefore, performed studies where the transport rates of two drugs, I-dopa and a-methyldopa were investigated in humans by using a validated perfusion approach (LennemBs et al. Pharm. Res. 9, 1243, 1992). We perfused the jejunal segment with a single-pass approach at 2.0 mUmin, and exposed the intestinal tissue for a drug concentration reflecting condition following an oral dose. The Peff-values were calculated according to the well-stirred model. These two drugs have been claimed to be transported across the intestinal mucosa by the transport protein for large neutral amino acids (LNAA). In this study we compared the Peff-value of Idopa and a-methyldopa in humans. We have previously shown that Peff for I-dopa at a luminal cont. of 2.5 mM decreased from 3.4. 1.5. 1.l when luminal cont. of I-leucine were 0,40 and 60 mM (Lenner& et al., Br. J. Clin. Pharm.; 1993, 35, 243.). The Peff-values for I-dopa at different luminal concentrations of 1.2, 2.5 and 5.0 mM were 3.3, 3.4 and 2.2 ‘lo-4 _..._. druo. cm/s, respectively. The Peff for the other ----. n-m&h - --.--.- yldopa. is rintwrninaxY __ ._ . . .__ *+ -. e_ luminal _. ._.conr~ntratinn _-. .__.. _.._. i918 mM, and it was 0.1 *lO-4 cm/s. This clear& demonstrates that I-dopa and a-methyldopa is classified as high and low permeability drugs, respectively, according to the Biopharmaceutical Drug Classification System. The ten-fold difference of the human Peff-estimates for these two drugs, probablv reflect a substantiallv lower affinttv of the carrier-mediated transport mechanism for a-methyldopa than-l-dopa.
Two different types of commonly used polymers tn various pharmaceutical products, the poly(acrylic actd) derlvatiies pofycarbophil (PCP) and carbomer 934P (C93dP. both from BF Goodrich. USA)as wellas the poly(amino glucan) chitosan, have recently shown to rmprove the intestinal transport of hydrophilic macromolecules in vffro [1.2]. The aim of thus study was to investigate whether these pobmers are able to improve the small Intestinal absorption of the LHRH superagonist buserelin (Hoechst, Germany) in viva As reported previously, PCP and C934P are able to inhibit the proteolytii activtty of trypsin. a-chymobypstn. carboxypeptiiase A 8 B and cytosolic aminopepbdase by deprivation of Ca” and Zn2’, respecttvaly. out of their enzyme structures [2.3]. Due to the stronger inhtbiiory effect of C934P. compared to PCP,a fast swelling one unit/two phase capsule dosage form with trypsin inhibiting properties based on carbomer modifications was developed [4]. Freeze-dried neutralized (pH 7.0) sodium C934P
(FNaC934P)was found to possess the best properties as a fast swelling C934P modification. Chitosan, however, showed no enzyma inhibitory effects [1,3], but was able to knprove paracellular transport of fluorescein isothiocyanate dextran (FD-4, Mw 4,400) and 9-desglycinamide. 6-argintne vasopressin in the Caco-2 cell monolayer model [1.2] For the in viva studies, male Wistar rats (190-2309) were fasted overnight before surgery. A teflon tube was introduced in the stomach and carefuffy forwarded through the pylorus into the duodenum. After application of 500 pg buserelin. dissolved in 2 ml of etther 0.5% (w/v) oolv(acrvlate) or 1.5%fw/v) chitosan-HCI (Pronova. Drammen. Norwavl drspersion tn f&S/t& buffer pH 6.7, ihe tube was removed from’the GM& and the inctsion in the stomach was closed immedtately. Blood samples ware withdrawn from the artena carotis at predetermined time pomts. During the experiment the rats were kept under ttypnonne/mtdazolam anaesthesia. The absolute bioavailabilities (C,,,, expressed as nq/ml), for the different polymer preparations were: control.0.V~ (6.7); 0.5% FNaC934P, 0.6% (45.6): OS%C934P. 2.0% (112.1) and chitosan-HCI, 5.1% (364.0). The higher btoavailability with chitosan-HCI compared to C924P and FNaC934P may suggest that for the peptide drug busarelin the transport enhancement effect plays a much more dominant role than the protection agarnst proteases. such as a-chymotrypstn. Chitoaan hydrcchbrlde wfth a bioavailability of 5.1% was comparable or even better than the reported btoavatlabilities of the nasal trade product Supre& (3.5 concluston. both types of polymers investigated showed a pronounced improvement of intestinal buserelin bioavailabiliiy. These findings indicate that C934P and chitosans are promising candidates as excipients tn peroral delivery systems for psptide drugs such as buserelin. [l] G. Borehard et al.. J. Controlted Ret (1996) tn press. Luerature; 121 H L. LusOen et al.. J. Conttdtad Rat. (1996) submkted for publication. (31 H.L. Lue6en et sl.. Eur. J. Pharm. Sci. (1996) in press. (4) Y Akivams et at.. tnt. J. Phamt. (1996) in press.
In
- 5%).
Sci. 4 Suppl. (1996)
S75-S76
s75
Nanoparticles have been studied extensively as carriers for oral delivery of peptides whose bioavailability is very low because of high hydrophilicity and instability in the gastrointestinal tract. This study evaluated the usefulness of nanoparticles composed of new graft copolymers having a hydrophobic backbone and hydrophilic branches, as carriers that enhance the absorption of peptides. Nanoparticles were prepared by the dispersion copolymerization of hydrophilic macromonomers with styrene. An aqueous dispersion of nanoparticies was mixed with salmon calcitonin @CT) dissolved in water prior to in vivo study. This mixture was administered orally at a dose of 0.25 mg sCT/kg body weight, to Sprague Dawley male rats that had been fasted overnight. After administration, the blood ionized calcium concentration was measured. When sCT encapsulated in nanoparticles was administered orally, the decrease in blood ionized calcium concentration was considerably greater than after oral administration of sCT in water. This decrease was affected by the macromonomer structure, and it was confirmed that the absorption of sCT was enhanced most strongly by nanoparticles having poly (N-isopropylacrylamlde) or pc$ (iisopropylacrylamide-co-acrylic acid) macromonomer chains. However, the calcium concentration changed less when the nanoparticle concentration was low. On the other hand, the molecular weight of macromonomers and the particle size of nanoparticles did not affect the change in calcium concentration. These nanoparticles were demonstrated to be useful carriers for enhancing peptide absorption via the gastrointestinal tract.
Solid Lipid Nanoparticles (SLN) are a particulate carrier system with a mean diameter between approximately 5Onm up to 1OOOnm. By applying high pressure homogenizetion SLN dispersions are obtained with a lower content of microparticles then in fat emulsions for parenteral nutrition. The high pressure homogenization allows cost effective production on large scale. Additionally SLN fulfill other requirements of the regulatory authorities, e.g. a sufficient long-term stability, a controlled drug release, the possibility of sterilizetii and a low in vivo toxicity. For optimized formulations a long-term stability over 3 years could be shown. An SLN formulation knorrvn to be physically instable was chosen to investigate the correlation between long-term stability and storage conditions. Storing instable SLN formulations at optirnel condiiions (low temperatures, in the dark) increased the long-term stabilii up to 2 years so far. In cese of occurring storage problems, the SLN dispersions can be lyophilized or alternatively spray dried. After optimizing the parameters, both methods lead to dry products which show after reconstiiution no or only little particle growth. SLN dispersions with an optimum composition oen be sterilized by autoctaving (at lPl”C, 2 bar) without alterations of the particle size. Even generelly less stable formulations can be autocfaved when reducing the lipid concentration from 10% to 2%. To investigate the release and entrapment behaviour prednisolone was chceen as a lipophilic model drug. Up to 30% of the drug ten be entrapped into the particles. Wti prednisokne loaded particles a controlled drug release over a rncnftored period of six weeks was achieved. The release behavior can be modtied by the surfeotant, the lipid matrix and the production temperamre. By choosing for example ow production ternperetures and low surfectent concentration a usteined drug release right from the beginning of the in vitmt issolution test can be achieved.
Delivery II I Eur. J. Pharm.
If a hydrophilic drug is a substrate for a canter-mediated transport mechanism across the jejunal mucosa, it will largely influence its total transport rate. The effective intestinal permeability (Peff) value will be influenced by the substrate affinity and the total transport capacity. Estimates of Peff-values for transport across the human mucosa in the small intestinal are lacking, since few studies have been performed This is mainly due to a lack of a human clinical investigation tool. We have therefore, performed studies where the transport rates of two drugs, I-dopa and a-methyldopa were investigated in humans by using a validated perfusion approach (LennemBs et al. Pharm. Res. 9, 1243, 1992). We perfused the jejunal segment with a single-pass approach at 2.0 mUmin, and exposed the intestinal tissue for a drug concentration reflecting condition following an oral dose. The Peff-values were calculated according to the well-stirred model. These two drugs have been claimed to be transported across the intestinal mucosa by the transport protein for large neutral amino acids (LNAA). In this study we compared the Peff-value of Idopa and a-methyldopa in humans. We have previously shown that Peff for I-dopa at a luminal cont. of 2.5 mM decreased from 3.4. 1.5. 1.l when luminal cont. of I-leucine were 0,40 and 60 mM (Lenner& et al., Br. J. Clin. Pharm.; 1993, 35, 243.). The Peff-values for I-dopa at different luminal concentrations of 1.2, 2.5 and 5.0 mM were 3.3, 3.4 and 2.2 ‘lo-4 _..._. druo. cm/s, respectively. The Peff for the other ----. n-m&h - --.--.- yldopa. is rintwrninaxY __ ._ . . .__ *+ -. e_ luminal _. ._.conr~ntratinn _-. .__.. _.._. i918 mM, and it was 0.1 *lO-4 cm/s. This clear& demonstrates that I-dopa and a-methyldopa is classified as high and low permeability drugs, respectively, according to the Biopharmaceutical Drug Classification System. The ten-fold difference of the human Peff-estimates for these two drugs, probablv reflect a substantiallv lower affinttv of the carrier-mediated transport mechanism for a-methyldopa than-l-dopa.
Two different types of commonly used polymers tn various pharmaceutical products, the poly(acrylic actd) derlvatiies pofycarbophil (PCP) and carbomer 934P (C93dP. both from BF Goodrich. USA)as wellas the poly(amino glucan) chitosan, have recently shown to rmprove the intestinal transport of hydrophilic macromolecules in vffro [1.2]. The aim of thus study was to investigate whether these pobmers are able to improve the small Intestinal absorption of the LHRH superagonist buserelin (Hoechst, Germany) in viva As reported previously, PCP and C934P are able to inhibit the proteolytii activtty of trypsin. a-chymobypstn. carboxypeptiiase A 8 B and cytosolic aminopepbdase by deprivation of Ca” and Zn2’, respecttvaly. out of their enzyme structures [2.3]. Due to the stronger inhtbiiory effect of C934P. compared to PCP,a fast swelling one unit/two phase capsule dosage form with trypsin inhibiting properties based on carbomer modifications was developed [4]. Freeze-dried neutralized (pH 7.0) sodium C934P
(FNaC934P)was found to possess the best properties as a fast swelling C934P modification. Chitosan, however, showed no enzyma inhibitory effects [1,3], but was able to knprove paracellular transport of fluorescein isothiocyanate dextran (FD-4, Mw 4,400) and 9-desglycinamide. 6-argintne vasopressin in the Caco-2 cell monolayer model [1.2] For the in viva studies, male Wistar rats (190-2309) were fasted overnight before surgery. A teflon tube was introduced in the stomach and carefuffy forwarded through the pylorus into the duodenum. After application of 500 pg buserelin. dissolved in 2 ml of etther 0.5% (w/v) oolv(acrvlate) or 1.5%fw/v) chitosan-HCI (Pronova. Drammen. Norwavl drspersion tn f&S/t& buffer pH 6.7, ihe tube was removed from’the GM& and the inctsion in the stomach was closed immedtately. Blood samples ware withdrawn from the artena carotis at predetermined time pomts. During the experiment the rats were kept under ttypnonne/mtdazolam anaesthesia. The absolute bioavailabilities (C,,,, expressed as nq/ml), for the different polymer preparations were: control.0.V~ (6.7); 0.5% FNaC934P, 0.6% (45.6): OS%C934P. 2.0% (112.1) and chitosan-HCI, 5.1% (364.0). The higher btoavailability with chitosan-HCI compared to C924P and FNaC934P may suggest that for the peptide drug busarelin the transport enhancement effect plays a much more dominant role than the protection agarnst proteases. such as a-chymotrypstn. Chitoaan hydrcchbrlde wfth a bioavailability of 5.1% was comparable or even better than the reported btoavatlabilities of the nasal trade product Supre& (3.5 concluston. both types of polymers investigated showed a pronounced improvement of intestinal buserelin bioavailabiliiy. These findings indicate that C934P and chitosans are promising candidates as excipients tn peroral delivery systems for psptide drugs such as buserelin. [l] G. Borehard et al.. J. Controlted Ret (1996) tn press. Luerature; 121 H L. LusOen et al.. J. Conttdtad Rat. (1996) submkted for publication. (31 H.L. Lue6en et sl.. Eur. J. Pharm. Sci. (1996) in press. (4) Y Akivams et at.. tnt. J. Phamt. (1996) in press.
In
- 5%).
Sci. 4 Suppl. (1996)
S75-S76
s75
Nanoparticles have been studied extensively as carriers for oral delivery of peptides whose bioavailability is very low because of high hydrophilicity and instability in the gastrointestinal tract. This study evaluated the usefulness of nanoparticles composed of new graft copolymers having a hydrophobic backbone and hydrophilic branches, as carriers that enhance the absorption of peptides. Nanoparticles were prepared by the dispersion copolymerization of hydrophilic macromonomers with styrene. An aqueous dispersion of nanoparticies was mixed with salmon calcitonin @CT) dissolved in water prior to in vivo study. This mixture was administered orally at a dose of 0.25 mg sCT/kg body weight, to Sprague Dawley male rats that had been fasted overnight. After administration, the blood ionized calcium concentration was measured. When sCT encapsulated in nanoparticles was administered orally, the decrease in blood ionized calcium concentration was considerably greater than after oral administration of sCT in water. This decrease was affected by the macromonomer structure, and it was confirmed that the absorption of sCT was enhanced most strongly by nanoparticles having poly (N-isopropylacrylamlde) or pc$ (iisopropylacrylamide-co-acrylic acid) macromonomer chains. However, the calcium concentration changed less when the nanoparticle concentration was low. On the other hand, the molecular weight of macromonomers and the particle size of nanoparticles did not affect the change in calcium concentration. These nanoparticles were demonstrated to be useful carriers for enhancing peptide absorption via the gastrointestinal tract.
Solid Lipid Nanoparticles (SLN) are a particulate carrier system with a mean diameter between approximately 5Onm up to 1OOOnm. By applying high pressure homogenizetion SLN dispersions are obtained with a lower content of microparticles then in fat emulsions for parenteral nutrition. The high pressure homogenization allows cost effective production on large scale. Additionally SLN fulfill other requirements of the regulatory authorities, e.g. a sufficient long-term stability, a controlled drug release, the possibility of sterilizetii and a low in vivo toxicity. For optimized formulations a long-term stability over 3 years could be shown. An SLN formulation knorrvn to be physically instable was chosen to investigate the correlation between long-term stability and storage conditions. Storing instable SLN formulations at optirnel condiiions (low temperatures, in the dark) increased the long-term stabilii up to 2 years so far. In cese of occurring storage problems, the SLN dispersions can be lyophilized or alternatively spray dried. After optimizing the parameters, both methods lead to dry products which show after reconstiiution no or only little particle growth. SLN dispersions with an optimum composition oen be sterilized by autoctaving (at lPl”C, 2 bar) without alterations of the particle size. Even generelly less stable formulations can be autocfaved when reducing the lipid concentration from 10% to 2%. To investigate the release and entrapment behaviour prednisolone was chceen as a lipophilic model drug. Up to 30% of the drug ten be entrapped into the particles. Wti prednisokne loaded particles a controlled drug release over a rncnftored period of six weeks was achieved. The release behavior can be modtied by the surfeotant, the lipid matrix and the production temperamre. By choosing for example ow production ternperetures and low surfectent concentration a usteined drug release right from the beginning of the in vitmt issolution test can be achieved.