Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) prod... more Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) products can take up to 2h to disintegrate in the human small intestine, which clearly highlights the inadequacy of the in vitro test method to predict in vivo behaviour of these formulations. The aim of this study was to establish the utility of a novel pH 5.6 bicarbonate buffer, stabilized by an Auto pH™ system, as a better surrogate of the conditions of the proximal small intestine to investigate the dissolution behaviour of standard and accelerated release enteric double coating formulations. Prednisolone tablets were coated with 3 or 5mg/cm2 of partially neutralized EUDRAGIT® L 30 D-55, HP-55 or HPMC adjusted to pH 6 or 8. An outer layer of EUDRAGIT® L 30 D-55 was applied at 5mg/cm2. For comparison purposes, a standard single layer of EUDRAGIT® L 30 D-55 was applied to the tablets. Dissolution was carried out using USP II apparatus in 0.1M HCl for 2h, followed by pH 5.6 bicarbonate buffer. EUDRAGIT® L 30 D-55 single-coated tablets showed a slow drug release with a lag time of 75min in buffer, whereas release from the EUDRAGIT® L 30 D-55 double-coated tablets was accelerated. These in vitro lag times closely match the in vivo disintegration times for these coated tablets reported previously. Drug release was further accelerated from modified double coatings, particularly in the case of coatings with a thinner inner layer of HP-55 or HPMC (pH 8 and KH2PO4). This study confirms that the pH 5.6 bicarbonate buffer system offers significant advantages in the development of dosage forms designed to release in the upper small intestine.
Oral modified-release dosage forms can be designed with the aim of achieving specific pharmacokin... more Oral modified-release dosage forms can be designed with the aim of achieving specific pharmacokinetic profiles, delivering to specific gut localities or reducing the number of drug administrations. Multiple-unit systems, such as pellets, beads or granules, often claim superiority to single-unit modified-release formulations in terms of predictability and reproducibility of behaviour in the gastrointestinal tract. This is an oversimplification and in this review we discuss the effect of the highly variable gastrointestinal transit on the bioperformance of multiple-unit dosage forms, relative to their single-unit counterparts. We examine the sometimes contradictory literature in this area and highlight specific case studies which demonstrate the effect of intestinal transit on dosage form performance and drug absorption.
Age-mediated changes in gut physiology are considerations central to the elucidation of drug perf... more Age-mediated changes in gut physiology are considerations central to the elucidation of drug performance from oral formulations. Using rats of different age groups we measured the pH, buffer capacity, fluid volume, osmolality, and surface tension of gastrointestinal (GI) fluids, and therein explored the impact of these variables on prednisolone and mesalazine solubility in luminal fluids. We also studied the distribution of gut associated lymphoid tissue (GALT) and mucus layer thickness across the GI tract in rats of different age groups. At a mucosal level, there was an increase in GALT from young to adult rat. Gastrointestinal pH and buffer capacity remained mostly unchanged with age, except some pH differences in stomach and distal small intestine and a higher buffer capacity in the large intestinal fluids of young rats. Osmolality and surface tension also remained unaffected with the exception of a lower osmolality in elderly stomach and a lower surface tension in the small intestine of young rats. The difference in luminal environment on ageing influenced the solubility of studied drugs, for instance prednisolone solubility was shown to be higher in adult rats (mid small intestine and caecum) and solubility of mesalazine was significantly higher in the elderly distal small intestine.
Oral delivery of biologicals is a thriving field in pharmaceutics and the first challenge is to a... more Oral delivery of biologicals is a thriving field in pharmaceutics and the first challenge is to achieve a stable drug product. Interesting is prilling of a drug-containing polymeric solution as microgel into an aqueous hardening bath where crosslinking occurs. However, to deliver a final dosage form, for example, soft gelatin capsules, the aqueous hardening bath must be removed, thus leading to manufacturing processes that are potentially harmful for the active. The current work introduces a prilling method with a lipid-based hardening bath, which could theoretically be filled directly into capsules. Bovine serum albumin (BSA) and mono-N-carboxymethyl chitosan (MCC) were selected as model biological and encapsulating polymer, respectively. Several nonaqueous formulations of the receiving bath were investigated; calcium chloride was added to these formulations to allow the MCC gelling. The obtained microgels had average diameters of ∼300 μm and spherical to toroidal shapes, according...
Gastrointestinal physiology is dynamic and complex at the best of times, and a multitude of known... more Gastrointestinal physiology is dynamic and complex at the best of times, and a multitude of known variables can affect the overall bioavailability of drugs delivered via the oral route. Yet while the influences of food and beverage intake as just two of these variables on oral drug delivery have been extensively documented in the wider literature, specific information on their effects remains sporadic, and is not so much contextually reviewed. Food co-ingestion with oral dosage forms can mediate several changes to drug bioavailability, yet the precise mechanisms underlying this have yet to be fully elucidated. Likewise, the often detrimental effects of alcohol (ethanol) on dosage form performance have been widely observed experimentally, but knowledge of which has only moderately impacted on clinical practice. Here, we attempt to piece together the available subject matter relating to the influences of both solid and liquid foodstuffs on the gastrointestinal milieu and the implications for oral drug delivery, with particular emphasis on the behaviour of modified-release dosage forms, formulation robustness and drug absorption. Providing better insight into these influences, and exemplifying cases where formulations have been developed or modified to circumvent their associated problems, can help to appropriately direct the design of future in vitro digestive modelling systems as well as oral dosage forms resilient to these effects. Moreover, this will help to better our understanding of the impact of food and alcohol intake on normal gut behaviour and function.
Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) prod... more Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) products can take up to 2 h to disintegrate in the human small intestine, which clearly highlights the inadequacy of the in vitro test method to predict in vivo behaviour of these formulations. The aim of this study was to establish the utility of a novel pH 5.6 bicarbonate buffer, stabilized by an Auto pH™ System, as a better surrogate of the conditions of the proximal small intestine to investigate the dissolution behaviour of standard and accelerated release enteric double coating formulations. Prednisolone tablets were coated with 3 or 5 mg/cm(2) of partially neutralized EUDRAGIT(®) L 30 D-55, HP-55 or HPMC adjusted to pH 6 or 8. An outer layer of EUDRAGIT(®) L 30 D-55 was applied at 5mg/cm(2). For comparison purposes, a standard single layer of EUDRAGIT(®) L 30 D-55 was applied to the tablets. Dissolution was carried out using USP II apparatus in 0.1 M HCl for 2 h, followed by pH 5.6 bi...
European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences, 2014
Age-mediated changes in gut physiology are considerations central to the elucidation of drug perf... more Age-mediated changes in gut physiology are considerations central to the elucidation of drug performance from oral formulations. Using rats of different age groups we measured the pH, buffer capacity, fluid volume, osmolality, and surface tension of gastrointestinal (GI) fluids, and therein explored the impact of these variables on prednisolone and mesalazine solubility in luminal fluids. We also studied the distribution of gut associated lymphoid tissue (GALT) and mucus layer thickness across the GI tract in rats of different age groups. At a mucosal level, there was an increase in GALT from young to adult rat. Gastrointestinal pH and buffer capacity remained mostly unchanged with age, except some pH differences in stomach and distal small intestine and a higher buffer capacity in the large intestinal fluids of young rats. Osmolality and surface tension also remained unaffected with the exception of a lower osmolality in elderly stomach and a lower surface tension in the small inte...
A novel platform system, comprising a mucoadhesive core and a rapid release carrier, was designed... more A novel platform system, comprising a mucoadhesive core and a rapid release carrier, was designed for targeted drug delivery to the colon. Prednisolone pellets containing different carbomers, including Carbopol 971P, Carbopol 974P and Polycarbophil AA-1, with or without organic acids, were produced by extrusion-spheronization. Mucoadhesive pellets were coated with a new enteric double-coating system, which dissolves at pH 7. This system comprises an inner layer of partially neutralized Eudragit S and buffer salt and an outer coating of standard Eudragit S. A single layer of standard Eudragit S was also applied for comparison purposes. Dissolution of the coated pellets was assessed in USP II apparatus in 0.1N HCl followed by Krebs bicarbonate buffer pH 7.4. Visualization of the coating dissolution process was performed by confocal laser scanning microscopy using fluorescent markers in both layers. The mucoadhesive properties of uncoated, single-coated and-double coated pellets were evaluated ex vivo on porcine colonic mucosa. Mucoadhesive pellets coated with a single layer of Eudragit S release its cargo after a lag time of 120 min in Krebs buffer. In contrast, drug release from the double-coated mucoadhesive pellets was significantly accelerated, starting at 75 min. In addition, the mucoadhesive properties of the core of the double coated pellets were higher than those from single-coated pellets after the core had been exposed to the buffer medium. This novel platform technology has the potential to target the colon and overcome the variability in transit and harmonize drug release and bioavailability.
Objectives The objective of this study was to systematically assess the mucus thickness in the ga... more Objectives The objective of this study was to systematically assess the mucus thickness in the gastrointestinal tract of laboratory animals commonly used in preclinical studies. Methods Mucus thickness was studied post-mortem in the rat, rabbit and pig, using cryosections stained by the modified periodic acid Schiff/Alcian blue method. Key findings The mucus thickness in the fundus region of the stomach was higher in the pig (190.7 Ϯ 80.7 mm) than in the rabbit (155.1 Ϯ 85.8 mm) and the rat (31.3 Ϯ 11.4 mm). However, along the small intestine (ileum), mucus was thicker in the rabbit (147.8 Ϯ 115.6 mm), followed by the pig (53.8 Ϯ 22.1 mm) and the rat (34.1 Ϯ 14.9 mm). This rank order was also observed in the ascending colon. Conclusions Inter-species variability in mucus thickness along the gut was demonstrated and suggests that the pig resembles more closely the mucus pattern of humans. This may be highly relevant when preclinical animal models are used in drug absorption studies or in the development of oral mucoadhesive drug delivery systems.
European Journal of Pharmaceutics and Biopharmaceutics, 2014
Drug loading into porous carriers may improve drug release of poorly water-soluble drugs. However... more Drug loading into porous carriers may improve drug release of poorly water-soluble drugs. However, the widely used impregnation method based on adsorption lacks reproducibility and efficiency for certain compounds. The aim of this study was to evaluate a drug-loading method based on solvent evaporation and crystallization, and to investigate the underlying drug-loading mechanisms. Functionalized calcium carbonate (FCC) microparticles and four drugs with different solubility and permeability properties were selected as model substances to investigate drug loading. Ibuprofen, nifedipine, losartan potassium, and metronidazole benzoate were dissolved in acetone or methanol. After dispersion of FCC, the solvent was removed under reduced pressure. For each model drug, a series of drug loads were produced ranging from 25% to 50% (w/w) in steps of 5% (w/w). Loading efficiency was qualitatively analyzed by scanning electron microscopy (SEM) using the presence of agglomerates and drug crystals as indicators of poor loading efficiency. The particles were further characterized by mercury porosimetry, specific surface area measurements, differential scanning calorimetry, and USP 2 dissolution. Drug concentration was determined by HPLC. FCC-drug mixtures containing equivalent drug fractions but without specific loading strategy served as reference samples. SEM analysis revealed high efficiency of pore filling up to a drug load of 40% (w/w). Above this, agglomerates and separate crystals were significantly increased, indicating that the maximum capacity of drug loading was reached. Intraparticle porosity and specific surface area were decreased after drug loading because of pore filling and crystallization on the pore surface. HPLC quantification of drugs taken up by FCC showed only minor drug loss. Dissolution rate of FCC loaded with metronidazole benzoate and nifedipine was faster than the corresponding FCC-drug mixtures, mainly due to surface enlargement, because only small fractions of amorphous drug (12.5%, w/w, and 8.9%, w/w, respectively) were found by thermal analysis. Combination of qualitative SEM analysis and HPLC quantification was sufficient to proof the feasibility of the solvent-evaporation method for the loading of various drugs into FCC. Mechanistic investigation revealed that a high specific surface area of the carrier is required to facilitate heterogeneous nucleation, and large pore sizes (up to 1 lm) are beneficial to reduce crystallization pressures and allow drug deposition within the pores. The solvent-evaporation method allows precise drug loading and appears to be suitable for scale-up.
Critical Reviews in Therapeutic Drug Carrier Systems, 2008
The concept of mucoadhesion is one that has the potential to improve the highly variable residenc... more The concept of mucoadhesion is one that has the potential to improve the highly variable residence times experienced by drugs and dosage forms at various sites in the gastrointestinal tract, and consequently, to reduce variability and improve efficacy. Intimate contact with the mucosa should enhance absorption or improve topical therapy. A variety of approaches have been investigated for mucoadhesion in the gastrointestinal tract, particularly for the stomach and small intestine. Despite interesting results in these sites, mucoadhesive approaches have not yet shown success in humans. The potential of the lower gut for these applications has been largely neglected, although the large intestine in particular may benefit, and the colon has several factors that suggest mucoadhesion could be successful there, including lower motility and the possibility of a lower mucus turnover and thicker mucus layer. In vitro studies on colonic mucoadhesion show promise, and rectal administration has shown some positive results in vivo. This review considers the background to mucoadhesion with respect to the physiological conditions of the gastrointestinal tract as well as the principles that underlie this concept. Mucoadhesive approaches to gastrointestinal drug delivery will be examined, with particular attention given to the lower gut.
Oral modified-release dosage forms can be designed with the aim of achieving specific pharmacokin... more Oral modified-release dosage forms can be designed with the aim of achieving specific pharmacokinetic profiles, delivering to specific gut localities or reducing the number of drug administrations. Multiple-unit systems, such as pellets, beads or granules, often claim superiority to single-unit modified-release formulations in terms of predictability and reproducibility of behaviour in the gastrointestinal tract. This is an oversimplification and in this review we discuss the effect of the highly variable gastrointestinal transit on the bioperformance of multiple-unit dosage forms, relative to their single-unit counterparts. We examine the sometimes contradictory literature in this area and highlight specific case studies which demonstrate the effect of intestinal transit on dosage form performance and drug absorption.
Revista Brasileira De Ciencias Farmaceuticas, 2008
The oral bioavailability of many drugs can be limited by the residence time of pharmaceutical dos... more The oral bioavailability of many drugs can be limited by the residence time of pharmaceutical dosage forms in the gastrointestinal tract. Mucoadhesion has been proposed as a method to increase residence time at a specific area, hence increasing the therapeutic effect of drugs. Most research efforts on mucoadhesion have focused on the stomach and small intestine, with promising results observed from in in vitro studies. However, γ-scintigraphy data obtained in human studies have revealed the lack of success of mucoadhesion approaches in order to increase the contact time of formulations in the upper gut. The lack of in vitro/in vivo correlation can be attributed to the complex nature of the human gastrointestinal tract, with most in vitro models providing little resemblance to the in vivo situation, such as motility, pH, mucus thickness and mucus turnover, presence of enzymes and food. In the colon, the mucus turnover, the sensibility to mucus secretory stimulus and motility are lower than in the stomach and small intestine. Therefore, colonic mucoadhesion may be a more successful approach. Nevertheless, more studies in animals and humans are needed to evaluate its potential, as well as, pharmacokinetic studies to investigate drug release and absorption from mucoadhesive systems.
Mucoadhesion in the gastrointestinal tract is a complex phenomenon and both formulation and physi... more Mucoadhesion in the gastrointestinal tract is a complex phenomenon and both formulation and physiological features need to be well understood and considered. Mucus thickness has been inferred to play a role in this process; however no definitive influence has been established. This study aimed to investigate the influence of mucus thickness on the mucoadhesion process, using a large animal (pig) as a model to closely resemble the human physiological features. The mucus thickness of different regions of the gastrointestinal tract of pig was fully measured by means of a histochemical method (hematoxilin/eosin) employing cryostat sections. Mucoadhesion was evaluated ex vivo on porcine mucosa by tensiometry using a polyacrylic acid polymer (Carbopol 974P NF) as a mucoadhesive model material, both in a dry and swollen state. Mucus was thickest in the stomach (body 67.9+/-54.7 microm) and mucus thickness increased from proximal to distal segments in both the small intestine (duodenum 25.9+/-11.8 microm, ileum 31.0+/-15.7 microm) and large intestine (caecum 19.4+/-8.7 microm, ascending colon 31.9+/-17.2 microm, descending colon 35.1+/-16.0 microm and rectum 40.8+/-12.5 microm). Swollen polymer exhibited lower mucoadhesion than the dry form in all sections analysed. Mucus thickness plays a role on the mucoadhesion, as thicker mucus provides deeper polymer chain diffusion and entanglements; however, other factors are also involved in this complex process.
Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) prod... more Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) products can take up to 2h to disintegrate in the human small intestine, which clearly highlights the inadequacy of the in vitro test method to predict in vivo behaviour of these formulations. The aim of this study was to establish the utility of a novel pH 5.6 bicarbonate buffer, stabilized by an Auto pH™ system, as a better surrogate of the conditions of the proximal small intestine to investigate the dissolution behaviour of standard and accelerated release enteric double coating formulations. Prednisolone tablets were coated with 3 or 5mg/cm2 of partially neutralized EUDRAGIT® L 30 D-55, HP-55 or HPMC adjusted to pH 6 or 8. An outer layer of EUDRAGIT® L 30 D-55 was applied at 5mg/cm2. For comparison purposes, a standard single layer of EUDRAGIT® L 30 D-55 was applied to the tablets. Dissolution was carried out using USP II apparatus in 0.1M HCl for 2h, followed by pH 5.6 bicarbonate buffer. EUDRAGIT® L 30 D-55 single-coated tablets showed a slow drug release with a lag time of 75min in buffer, whereas release from the EUDRAGIT® L 30 D-55 double-coated tablets was accelerated. These in vitro lag times closely match the in vivo disintegration times for these coated tablets reported previously. Drug release was further accelerated from modified double coatings, particularly in the case of coatings with a thinner inner layer of HP-55 or HPMC (pH 8 and KH2PO4). This study confirms that the pH 5.6 bicarbonate buffer system offers significant advantages in the development of dosage forms designed to release in the upper small intestine.
Oral modified-release dosage forms can be designed with the aim of achieving specific pharmacokin... more Oral modified-release dosage forms can be designed with the aim of achieving specific pharmacokinetic profiles, delivering to specific gut localities or reducing the number of drug administrations. Multiple-unit systems, such as pellets, beads or granules, often claim superiority to single-unit modified-release formulations in terms of predictability and reproducibility of behaviour in the gastrointestinal tract. This is an oversimplification and in this review we discuss the effect of the highly variable gastrointestinal transit on the bioperformance of multiple-unit dosage forms, relative to their single-unit counterparts. We examine the sometimes contradictory literature in this area and highlight specific case studies which demonstrate the effect of intestinal transit on dosage form performance and drug absorption.
Age-mediated changes in gut physiology are considerations central to the elucidation of drug perf... more Age-mediated changes in gut physiology are considerations central to the elucidation of drug performance from oral formulations. Using rats of different age groups we measured the pH, buffer capacity, fluid volume, osmolality, and surface tension of gastrointestinal (GI) fluids, and therein explored the impact of these variables on prednisolone and mesalazine solubility in luminal fluids. We also studied the distribution of gut associated lymphoid tissue (GALT) and mucus layer thickness across the GI tract in rats of different age groups. At a mucosal level, there was an increase in GALT from young to adult rat. Gastrointestinal pH and buffer capacity remained mostly unchanged with age, except some pH differences in stomach and distal small intestine and a higher buffer capacity in the large intestinal fluids of young rats. Osmolality and surface tension also remained unaffected with the exception of a lower osmolality in elderly stomach and a lower surface tension in the small intestine of young rats. The difference in luminal environment on ageing influenced the solubility of studied drugs, for instance prednisolone solubility was shown to be higher in adult rats (mid small intestine and caecum) and solubility of mesalazine was significantly higher in the elderly distal small intestine.
Oral delivery of biologicals is a thriving field in pharmaceutics and the first challenge is to a... more Oral delivery of biologicals is a thriving field in pharmaceutics and the first challenge is to achieve a stable drug product. Interesting is prilling of a drug-containing polymeric solution as microgel into an aqueous hardening bath where crosslinking occurs. However, to deliver a final dosage form, for example, soft gelatin capsules, the aqueous hardening bath must be removed, thus leading to manufacturing processes that are potentially harmful for the active. The current work introduces a prilling method with a lipid-based hardening bath, which could theoretically be filled directly into capsules. Bovine serum albumin (BSA) and mono-N-carboxymethyl chitosan (MCC) were selected as model biological and encapsulating polymer, respectively. Several nonaqueous formulations of the receiving bath were investigated; calcium chloride was added to these formulations to allow the MCC gelling. The obtained microgels had average diameters of ∼300 μm and spherical to toroidal shapes, according...
Gastrointestinal physiology is dynamic and complex at the best of times, and a multitude of known... more Gastrointestinal physiology is dynamic and complex at the best of times, and a multitude of known variables can affect the overall bioavailability of drugs delivered via the oral route. Yet while the influences of food and beverage intake as just two of these variables on oral drug delivery have been extensively documented in the wider literature, specific information on their effects remains sporadic, and is not so much contextually reviewed. Food co-ingestion with oral dosage forms can mediate several changes to drug bioavailability, yet the precise mechanisms underlying this have yet to be fully elucidated. Likewise, the often detrimental effects of alcohol (ethanol) on dosage form performance have been widely observed experimentally, but knowledge of which has only moderately impacted on clinical practice. Here, we attempt to piece together the available subject matter relating to the influences of both solid and liquid foodstuffs on the gastrointestinal milieu and the implications for oral drug delivery, with particular emphasis on the behaviour of modified-release dosage forms, formulation robustness and drug absorption. Providing better insight into these influences, and exemplifying cases where formulations have been developed or modified to circumvent their associated problems, can help to appropriately direct the design of future in vitro digestive modelling systems as well as oral dosage forms resilient to these effects. Moreover, this will help to better our understanding of the impact of food and alcohol intake on normal gut behaviour and function.
Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) prod... more Despite rapid dissolution in compendial phosphate buffers, gastro resistant (enteric coated) products can take up to 2 h to disintegrate in the human small intestine, which clearly highlights the inadequacy of the in vitro test method to predict in vivo behaviour of these formulations. The aim of this study was to establish the utility of a novel pH 5.6 bicarbonate buffer, stabilized by an Auto pH™ System, as a better surrogate of the conditions of the proximal small intestine to investigate the dissolution behaviour of standard and accelerated release enteric double coating formulations. Prednisolone tablets were coated with 3 or 5 mg/cm(2) of partially neutralized EUDRAGIT(®) L 30 D-55, HP-55 or HPMC adjusted to pH 6 or 8. An outer layer of EUDRAGIT(®) L 30 D-55 was applied at 5mg/cm(2). For comparison purposes, a standard single layer of EUDRAGIT(®) L 30 D-55 was applied to the tablets. Dissolution was carried out using USP II apparatus in 0.1 M HCl for 2 h, followed by pH 5.6 bi...
European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences, 2014
Age-mediated changes in gut physiology are considerations central to the elucidation of drug perf... more Age-mediated changes in gut physiology are considerations central to the elucidation of drug performance from oral formulations. Using rats of different age groups we measured the pH, buffer capacity, fluid volume, osmolality, and surface tension of gastrointestinal (GI) fluids, and therein explored the impact of these variables on prednisolone and mesalazine solubility in luminal fluids. We also studied the distribution of gut associated lymphoid tissue (GALT) and mucus layer thickness across the GI tract in rats of different age groups. At a mucosal level, there was an increase in GALT from young to adult rat. Gastrointestinal pH and buffer capacity remained mostly unchanged with age, except some pH differences in stomach and distal small intestine and a higher buffer capacity in the large intestinal fluids of young rats. Osmolality and surface tension also remained unaffected with the exception of a lower osmolality in elderly stomach and a lower surface tension in the small inte...
A novel platform system, comprising a mucoadhesive core and a rapid release carrier, was designed... more A novel platform system, comprising a mucoadhesive core and a rapid release carrier, was designed for targeted drug delivery to the colon. Prednisolone pellets containing different carbomers, including Carbopol 971P, Carbopol 974P and Polycarbophil AA-1, with or without organic acids, were produced by extrusion-spheronization. Mucoadhesive pellets were coated with a new enteric double-coating system, which dissolves at pH 7. This system comprises an inner layer of partially neutralized Eudragit S and buffer salt and an outer coating of standard Eudragit S. A single layer of standard Eudragit S was also applied for comparison purposes. Dissolution of the coated pellets was assessed in USP II apparatus in 0.1N HCl followed by Krebs bicarbonate buffer pH 7.4. Visualization of the coating dissolution process was performed by confocal laser scanning microscopy using fluorescent markers in both layers. The mucoadhesive properties of uncoated, single-coated and-double coated pellets were evaluated ex vivo on porcine colonic mucosa. Mucoadhesive pellets coated with a single layer of Eudragit S release its cargo after a lag time of 120 min in Krebs buffer. In contrast, drug release from the double-coated mucoadhesive pellets was significantly accelerated, starting at 75 min. In addition, the mucoadhesive properties of the core of the double coated pellets were higher than those from single-coated pellets after the core had been exposed to the buffer medium. This novel platform technology has the potential to target the colon and overcome the variability in transit and harmonize drug release and bioavailability.
Objectives The objective of this study was to systematically assess the mucus thickness in the ga... more Objectives The objective of this study was to systematically assess the mucus thickness in the gastrointestinal tract of laboratory animals commonly used in preclinical studies. Methods Mucus thickness was studied post-mortem in the rat, rabbit and pig, using cryosections stained by the modified periodic acid Schiff/Alcian blue method. Key findings The mucus thickness in the fundus region of the stomach was higher in the pig (190.7 Ϯ 80.7 mm) than in the rabbit (155.1 Ϯ 85.8 mm) and the rat (31.3 Ϯ 11.4 mm). However, along the small intestine (ileum), mucus was thicker in the rabbit (147.8 Ϯ 115.6 mm), followed by the pig (53.8 Ϯ 22.1 mm) and the rat (34.1 Ϯ 14.9 mm). This rank order was also observed in the ascending colon. Conclusions Inter-species variability in mucus thickness along the gut was demonstrated and suggests that the pig resembles more closely the mucus pattern of humans. This may be highly relevant when preclinical animal models are used in drug absorption studies or in the development of oral mucoadhesive drug delivery systems.
European Journal of Pharmaceutics and Biopharmaceutics, 2014
Drug loading into porous carriers may improve drug release of poorly water-soluble drugs. However... more Drug loading into porous carriers may improve drug release of poorly water-soluble drugs. However, the widely used impregnation method based on adsorption lacks reproducibility and efficiency for certain compounds. The aim of this study was to evaluate a drug-loading method based on solvent evaporation and crystallization, and to investigate the underlying drug-loading mechanisms. Functionalized calcium carbonate (FCC) microparticles and four drugs with different solubility and permeability properties were selected as model substances to investigate drug loading. Ibuprofen, nifedipine, losartan potassium, and metronidazole benzoate were dissolved in acetone or methanol. After dispersion of FCC, the solvent was removed under reduced pressure. For each model drug, a series of drug loads were produced ranging from 25% to 50% (w/w) in steps of 5% (w/w). Loading efficiency was qualitatively analyzed by scanning electron microscopy (SEM) using the presence of agglomerates and drug crystals as indicators of poor loading efficiency. The particles were further characterized by mercury porosimetry, specific surface area measurements, differential scanning calorimetry, and USP 2 dissolution. Drug concentration was determined by HPLC. FCC-drug mixtures containing equivalent drug fractions but without specific loading strategy served as reference samples. SEM analysis revealed high efficiency of pore filling up to a drug load of 40% (w/w). Above this, agglomerates and separate crystals were significantly increased, indicating that the maximum capacity of drug loading was reached. Intraparticle porosity and specific surface area were decreased after drug loading because of pore filling and crystallization on the pore surface. HPLC quantification of drugs taken up by FCC showed only minor drug loss. Dissolution rate of FCC loaded with metronidazole benzoate and nifedipine was faster than the corresponding FCC-drug mixtures, mainly due to surface enlargement, because only small fractions of amorphous drug (12.5%, w/w, and 8.9%, w/w, respectively) were found by thermal analysis. Combination of qualitative SEM analysis and HPLC quantification was sufficient to proof the feasibility of the solvent-evaporation method for the loading of various drugs into FCC. Mechanistic investigation revealed that a high specific surface area of the carrier is required to facilitate heterogeneous nucleation, and large pore sizes (up to 1 lm) are beneficial to reduce crystallization pressures and allow drug deposition within the pores. The solvent-evaporation method allows precise drug loading and appears to be suitable for scale-up.
Critical Reviews in Therapeutic Drug Carrier Systems, 2008
The concept of mucoadhesion is one that has the potential to improve the highly variable residenc... more The concept of mucoadhesion is one that has the potential to improve the highly variable residence times experienced by drugs and dosage forms at various sites in the gastrointestinal tract, and consequently, to reduce variability and improve efficacy. Intimate contact with the mucosa should enhance absorption or improve topical therapy. A variety of approaches have been investigated for mucoadhesion in the gastrointestinal tract, particularly for the stomach and small intestine. Despite interesting results in these sites, mucoadhesive approaches have not yet shown success in humans. The potential of the lower gut for these applications has been largely neglected, although the large intestine in particular may benefit, and the colon has several factors that suggest mucoadhesion could be successful there, including lower motility and the possibility of a lower mucus turnover and thicker mucus layer. In vitro studies on colonic mucoadhesion show promise, and rectal administration has shown some positive results in vivo. This review considers the background to mucoadhesion with respect to the physiological conditions of the gastrointestinal tract as well as the principles that underlie this concept. Mucoadhesive approaches to gastrointestinal drug delivery will be examined, with particular attention given to the lower gut.
Oral modified-release dosage forms can be designed with the aim of achieving specific pharmacokin... more Oral modified-release dosage forms can be designed with the aim of achieving specific pharmacokinetic profiles, delivering to specific gut localities or reducing the number of drug administrations. Multiple-unit systems, such as pellets, beads or granules, often claim superiority to single-unit modified-release formulations in terms of predictability and reproducibility of behaviour in the gastrointestinal tract. This is an oversimplification and in this review we discuss the effect of the highly variable gastrointestinal transit on the bioperformance of multiple-unit dosage forms, relative to their single-unit counterparts. We examine the sometimes contradictory literature in this area and highlight specific case studies which demonstrate the effect of intestinal transit on dosage form performance and drug absorption.
Revista Brasileira De Ciencias Farmaceuticas, 2008
The oral bioavailability of many drugs can be limited by the residence time of pharmaceutical dos... more The oral bioavailability of many drugs can be limited by the residence time of pharmaceutical dosage forms in the gastrointestinal tract. Mucoadhesion has been proposed as a method to increase residence time at a specific area, hence increasing the therapeutic effect of drugs. Most research efforts on mucoadhesion have focused on the stomach and small intestine, with promising results observed from in in vitro studies. However, γ-scintigraphy data obtained in human studies have revealed the lack of success of mucoadhesion approaches in order to increase the contact time of formulations in the upper gut. The lack of in vitro/in vivo correlation can be attributed to the complex nature of the human gastrointestinal tract, with most in vitro models providing little resemblance to the in vivo situation, such as motility, pH, mucus thickness and mucus turnover, presence of enzymes and food. In the colon, the mucus turnover, the sensibility to mucus secretory stimulus and motility are lower than in the stomach and small intestine. Therefore, colonic mucoadhesion may be a more successful approach. Nevertheless, more studies in animals and humans are needed to evaluate its potential, as well as, pharmacokinetic studies to investigate drug release and absorption from mucoadhesive systems.
Mucoadhesion in the gastrointestinal tract is a complex phenomenon and both formulation and physi... more Mucoadhesion in the gastrointestinal tract is a complex phenomenon and both formulation and physiological features need to be well understood and considered. Mucus thickness has been inferred to play a role in this process; however no definitive influence has been established. This study aimed to investigate the influence of mucus thickness on the mucoadhesion process, using a large animal (pig) as a model to closely resemble the human physiological features. The mucus thickness of different regions of the gastrointestinal tract of pig was fully measured by means of a histochemical method (hematoxilin/eosin) employing cryostat sections. Mucoadhesion was evaluated ex vivo on porcine mucosa by tensiometry using a polyacrylic acid polymer (Carbopol 974P NF) as a mucoadhesive model material, both in a dry and swollen state. Mucus was thickest in the stomach (body 67.9+/-54.7 microm) and mucus thickness increased from proximal to distal segments in both the small intestine (duodenum 25.9+/-11.8 microm, ileum 31.0+/-15.7 microm) and large intestine (caecum 19.4+/-8.7 microm, ascending colon 31.9+/-17.2 microm, descending colon 35.1+/-16.0 microm and rectum 40.8+/-12.5 microm). Swollen polymer exhibited lower mucoadhesion than the dry form in all sections analysed. Mucus thickness plays a role on the mucoadhesion, as thicker mucus provides deeper polymer chain diffusion and entanglements; however, other factors are also involved in this complex process.
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