In vivo evaluation of a novel gastric retentive formulation based on ion exchange resins

An Overview on Polymethacrylate Polymers in Gastroretentive Dosage Forms

Drugs with lower bioavailability need repeated dosing to reach the minimum effective therapeutic concentration in plasma. In order to retain the drug in upper part of gastro intestinal tract (GIT) which is the major absorption window for majority of drugs and also to have localized effect many advances in drug delivery were made. Researchers mainly emphasize on to get patient compliance by formulating single dose, targeted and minimal side effects dosage form. The design must give constant drug release for longer time period that could be achieved through proper selection of polymers. These approaches in dosage design may also be advantageous for local action, to prevent drug degradation, delivery of gastro-irritant, narrow absorption window drugs and to get pH dependent release throughout the GIT. Polymethacrylate polymers in different ratios are available for the above objective as they are inert materials, could stay for longer time and are resistant to body fluids. This review also discusses the physicochemical properties of different available grades along with their glass transition temperatures (Tg).

Particle-stabilized emulsion droplets for gravity-mediated targeting in the posterior segment of the eye

This study tests the hypothesis that high-density particle-stabilized emulsion droplets (PEDs) can be designed to use gravity to target specific locations in the eye via suprachoroidal space injection. PEDs contain a core of high-density perfluorodecalin measuring ≤35 μm in diameter surrounded and stabilized by fluorescein-tagged, polystyrene nanoparticles that simulate polymeric drug carriers. A hollow microneedle infuses PEDs into the suprachoroidal space of rabbit eyes in vivo, which are later dissected and imaged to quantify distribution of fluorescent nanoparticles within the suprachoroidal space. With cornea oriented upward, such that gravity should move PEDs toward the back of the eye, up to 50% of nanoparticles are in the most posterior quadrant near the macula immediately after injection and 5 d later. With cornea oriented downward, to promote PED movement toward the front of the eye, approximately 60% of injected nanoparticles are targeted to the most anterior quadrant of the posterior segment near ciliary body. Injection of approximately neutral-density particles of the same size shows approximately equal distribution throughout the posterior segment. This study demonstrates for the first time that high-density PEDs can be used to deliver nanoparticles to specific locations in the back of the eye, including targeted delivery to the macula.

Decades of research in drug targeting to the upper gastrointestinal tract using gastroretention technologies: where do we stand?

A major constraint in oral controlled release drug delivery is that not all the drug candidates are absorbed uniformly throughout the gastrointestinal tract (GIT). Drugs having "absorption window" are absorbed in a particular portion of GIT only or are absorbed to a different extent in various segments of the GIT. Thus, only the drug released in the region preceding and in close vicinity to the absorption window is available for absorption. The drug must be released from the dosage form in solution form; otherwise, it is generally not absorbed. Hence, much research has been dedicated to the development of gastroretentive drug delivery systems that may optimize the bioavailability and subsequent therapeutic efficacy of such drugs, as these systems have unique properties to bypass the gastric emptying process. These systems show excellent in vitro results but fail to give desirable in vivo performance. During the last 2-3 decades, researchers from the academia and industries are giving considerable importance in this field. Unfortunately, till date, few so-called gastroretentive dosage forms have been brought to the market in spite of numerous academic publications. The manuscript considers strategies that are commonly used in the development of gastroretentive drug delivery systems with a special attention on various parameters, which needs to be monitored during formulation development.

Natural gum as mucoadhesive controlled release carriers: evaluation of cefpodoxime proxetil by D-optimal design technique

The present study deals with the development of mucoadhesive controlled release tablets of Cefpodoxime Proxetil to increase the gastric residence time and thus prolong drug release, reduce dosing frequency and improve oral bioavailability. Tablets were prepared using sodium alginate and karaya gum, a natural polymer, with a synthetic polymer hydroxypropylmethylcellulose (K100LV) and Karaya gum with HPMC K100LV in various ratios to optimize the drug release profile using D-Optimal technique. Pre- and post-compression parameters of tablets prepared with various formulations (S1-S9, C1-C9) were evaluated. The FTIR and DSC studies revealed that no physiochemical interaction between excipients and drug. The formulation S7 showed prolonged drug release, and the mechanism of drug release from the optimized formulation was confirmed using the Korsmeyer-Peppas model to be non-Fickian release transport and n value was found 0.605 indicating both diffusion and erosion mechanism from these natural gums. The optimized formulation showed mucoadhesive strength >35 g. An in vivo study was performed on rabbits using an X-ray imaging technique. The radiological evidence suggests that the tablets adheres (more than 10 hours) to a rabbit's stomach. No significant changes were found in the physical appearance, drug content, mucoadhesive study and in vitro dissolution pattern after storage at 40 °C/75% relative humidity for 3 months.

Loading and release of amine drugs by ion-exchange fibers: role of amine type

With more production and application of ion-exchange fibers (IEFs), it becomes necessary to understand the interaction between IEFs and amine compounds, an important group of organic drugs and structural components of large organic molecules in biological systems. However, so far few experimental studies have been conducted to systematically investigate the exchanging mechanism of amine compounds to IEFs. Therefore, 15 amine drugs were selected to investigate the effect of amine type on the loading and release of them from the related IEFs. Loading affinity of these drugs by IEFs decreased in the order of secondary, tertiary, and primary. The following items: basicity, aromaticity, molar volume, rotatability, and so on, were emphatically discussed to address the underlying mechanism of drug loading and releasing extent and rate of IEFs. It was evident that strong alkaline drugs strengthened the ionic bond between the amine groups and IEFs, and thus the loading affinity. These results will advance the understanding of the exchanging behavior of IEFs in the drug delivery system.

Silicone adhesive matrix of verapamil hydrochloride to provide pH-independent sustained release

Providing pH-independent oral release of weakly basic drugs with conventional matrix tablets can be challenging because of the pH-dependent solubility characteristics of the drugs and the changing pH environment along the gastrointestinal tract. The aim of the present study was to use a hydrophobic polymer to overcome the issue of pH-dependent release of weakly basic model drug verapamil hydrochloride from matrix tablets without the use of organic buffers in the matrix formulations. Silicone pressure-sensitive adhesive (PSA) polymer was evaluated because of its unique properties of low surface energy, hydrophobicity, low glass transition temperature, high electrical resistance, and barrier to hydrogen ion diffusion. Drug release, hydrogen ion diffusion, tablet contact angle, and internal tablet microenvironment pH with matrix tablets prepared using PSA were compared with those using water-insoluble ethyl cellulose (EC). Silicone PSA films showed higher resistance to hydrogen ion diffusion compared with EC films. Verapamil hydrochloride tablets prepared using silicone PSA showed higher hydrophobicity and lower water uptake than EC tablets. Silicone PSA tablets also showed pH-independent release of verapamil and decreased in dimensions during drug dissolution. By contrast, verapamil hydrochloride tablets prepared using EC did not achieve pH-independent release.

Gastroretentive mucoadhesive tablet of lafutidine for controlled release and enhanced bioavailability

Lafutidine a newly developed histamine H2-receptor antagonist having biological half-life of 1.92 ± 0.94 h due to its selective absorption from upper part of gastrointestinal tract the development of mucoadhesive sustained release drug delivery system is recommended in order to enhance the bioavailability. A mucoadhesive tablets was developed using the natural polymer, sodium alginate, xanthan gum and karaya gum. Mucoadhesion is a complex phenomenon which involves wetting, adsorption and interpenetration of polymer chains. The prepared tablets of various formulations were evaluated for a total mucoadhesion time, buoyancy lag time and percentage drug released. The formulation with xanthan gum showed better results. Thus, it may be useful for prolonged drug release in stomach to improve the bioavailability and reduced dosing frequency. Non-fickians release transport was confirmed as the drug release mechanism from the optimized formulation by Korsmeyer-Peppas. The optimized formulation (B3) showed a mucoadhesive strength >35 g. In vivo study was performed using rabbits by X-ray imaging technique. Radiological evidences suggest that, a formulated tablet was well adhered for >10 h in rabbit's stomach. Optimized lafutidine mucoadhesive tablets showed no significant change in physical appearance, drug content, mucoadhesive properties and in vitro dissolution pattern after storage at 40 °C temperature 75 ± 5% relative humidity for 3 months.

Preparation of multiple-unit floating-bioadhesive cooperative minitablets for improving the oral bioavailability of famotidine in rats

Abstract The aims of this study were to prepare fine famotidine-containing floating-bioadhesive cooperative minitablets and to investigate the possibility of using those minitablets as a delivery system for promoting the oral bioavailability of famotidine. Nine minitablet formulations were designed using hydroxypropylmethylcellulose (HPMC K4M) as release-retarding polymers, Carbopol 971P as bioadhesive materials and sodium bicarbonate (NaHCO3) as gas formers. The prepared 3 ± 0.02 mm minitablets were evaluated in terms of their swelling ability, floating behavior, bioadhesion test and in vitro release. The optimized minitablets (F6) containing HPMC K4M (50.00%, w/w), Carbopol 971P (10.00%, w/w) and NaHCO3 (10.00%, w/w) were found to float in 1 min and remain lastingly buoyant over a period of 8 h in vitro, with excellent bioadhesive properties (20.81 g) and sustained drug release characteristics (T50% = 46.54%) followed one-order model. In addition, plasma concentration-time profiles from pharmacokinetic studies in rats dosed with minitablets showed 1.62-fold (p < 0.05) increased absorption of famotidine, compared to the market tablets XinFaDing®. These studies demonstrated that the multiple-unit floating-bioadhesive cooperative minitablets may be a promising gastro-retentive delivery system for drugs that play a therapeutic role in the stomach.

A novel gastroretentive porous microparticle for anti-Helicobacter pylori therapy: preparation, in vitro and in vivo evaluation

Gastroretentive drug delivery system is a promising option for the treatment of Helicobacter pylori infection, which can prolong gastric residence time and supply high drug concentration in the stomach. In the present study, a low density system of metronidazole-loaded porous Eudragit® RS microparticle with high drug loading capacity (>25%) was fabricated via electrospray method. The porous structure and size distribution of microparticles were affected by polymer concentration and flow rate of solution. FTIR and XRD analyses indicated that drug has been entrapped into the porous microparticles. In addition, sustained release profiles and slight cytotoxicity in vitro were detected. Gamma scintigraphy study in vivo demonstrated that ¹³¹I-labeled microparticles retained in stomach for over 8h, and about 65.50% radioactive counts were finally detected in the region of interest. The biodistribution study confirmed that hotspot of radioactivity was remaining in the stomach. Furthermore, metronidazole-loaded porous microparticles can eradicate H. pylori completely with lower dose and administration frequency of antibiotic compared with pure drug, which were also more helpful for the healing of mucosal damages. These results suggest that prepared porous microparticle has the potential to provide better treatment for H. pylori infection.

Development of a gastric retentive system as a sustained-release formulation of pranlukast hydrate and its subsequent in vivo verification in human studies

Pranlukast hydrate was demonstrated in a human site-of-absorption study to have extremely poor absorption properties in the lower gastrointestinal tract. The ratios of AUC0-24 in the distal small bowel and colon compared to stomach delivery were approximately 1/7 and 1/70, respectively. As a consequence, a gastroretentive double-layered tablet formulation (gastric swelling system; GSS), consisting of a swelling layer and a drug release layer, was developed for once-daily dosing. To study the gastric retention of the optimized GSS, an in vivo gamma scintigraphic study was carried out in nine healthy volunteers. The transit profiles demonstrated that the GSS was retained in the stomach for more than 10h. The plasma profile was prolonged, especially following administration after an evening meal. The human data validated the design concept and suggest that GSS could be a promising approach for the development of sustained-release formulation for drugs with a limited absorption window in the upper small bowel.

Evaluation of in vivo behavior of controlled and pulsatile release pastilles using pharmacokinetic and γ-scintigraphic techniques

OBJECTIVE

To evaluate the in vivo behavior of controlled and pulsatile release pastilles for chronic treatment of asthma and chronic obstructive pulmonary disease (COPD) and for the chronotherapeutic management of nocturnal asthma, respectively.

RESEARCH DESIGN & METHODS

The prepared immediate release and controlled release pastilles were subjected to in vivo pharmacokinetic studies in rats. Whereas, pulsatile release formulation was subjected to γ-scintigraphic study in rats to study the gastrointestinal transit of the formulations and its results were correlated with the previous pharmacokinetic data.

RESULTS

The in vivo pharmacokinetic study of controlled release pastille formulation showed significant decrease in C(max) with increase in t(max), which indicates that the effect of dosage form would last for longer duration. Thus, the prepared formulation can be useful for the chronic treatment of asthma and COPD. The γ-scintigraphic study and pharmacokinetic data indicated that the pastilles coated with the enteric coat and the additional floating coat were effective in significantly delaying the in vivo drug release (by 4-5 h) required for the chronotherapeutic treatment of nocturnal asthma.

CONCLUSION

This study opens a new alternative to the conventional tablet or capsule dosage form for the development of both immediate and modified release drug delivery systems.

Development of a gastroretentive pulsatile drug delivery platform

Objectives

To develop a novel gastroretentive pulsatile drug delivery platform by combining the advantages of floating dosage forms for the stomach and pulsatile drug delivery systems.

Methods

A gastric fluid impermeable capsule body was used as a vessel to contain one or more drug layer(s) as well as one or more lag-time controlling layer(s). A controlled amount of air was sealed in the innermost portion of the capsule body to reduce the overall density of the drug delivery platform, enabling gastric floatation. An optimal mass fill inside the gastric fluid impermeable capsule body enabled buoyancy in a vertical orientation to provide a constant surface area for controlled erosion of the lag-time controlling layer. The lag-time controlling layer consisted of a swellable polymer, which rapidly formed a gel to seal the mouth of capsule body and act as a barrier to gastric fluid ingress.

Key findings

By varying the composition of the lag-time controlling layer, it was possible to selectively program the onset of the pulsatile delivery of a drug.

Conclusions

This new delivery platform offers a new method of delivery for a variety of suitable drugs targeted in chronopharmaceutical therapy. This strategy could ultimately improve drug efficacy and patient compliance, and reduce harmful side effects by scaling back doses of drug administered.

Gastroretentive microparticles for drug delivery applications

Many strategies have been proposed to explore the possibility of exploiting gastroretention for drug delivery. Such systems would be useful for local delivery, for drugs that are poorly soluble at higher pH or primarily absorbed from the proximal small intestine. Generally, the requirements of such strategies are that the vehicle maintains controlled drug release and exhibits prolonged residence time in the stomach. Despite widespread reporting of technologies, many have an inherent drawback of variability in transit times. Microparticulate systems, capable of distributing widely through the gastrointestinal tract, can potentially minimise this variation. While being retained in the stomach, the drug content is released slowly at a desired rate, resulting in reduced fluctuations in drug levels. This review summarises the promising role of microencapsulation in this field, exploring both floating and mucoadhesive microparticles and their application in the treatment of Helicobacter pylori, highlighting the clinical potential of eradication of this widespread infection.

Ion-exchange resins as drug delivery carriers

There are many reports in the literature referring to the utilization of drug bound to ion-exchange resin (drug-resinate), especially in the drug delivery area. Ion-exchange resin complexes, which can be prepared from both acidic and basic drugs, have been widely studied and marketed. Salts of cationic and anionic exchange resins are insoluble complexes in which drug release results from exchange of bound drug ions by ions normally present in body fluids. Resins used are polymers that contain appropriately substituted acidic groups, such as carboxylic and sulfonic for cation exchangers; or basic groups, such as quaternary ammonium group for anion exchangers. Variables relating to the resin are the exchange capacity; degree of cross-linking, which determines the permeability of the resin, its swelling potential, and the access of the exchange sites to the drug ion; the effective pK(a) of the exchanging group, which determines the exchange affinity; and the resin particle size, which controls accessibility to the exchange ions. In this review, the properties of ion-exchange resins, selection of drugs that lend themselves to such an approach, selection of the appropriate resin, preparation of drug-resinate, evaluation of drug release, recent developments of drug-resinates, and applications are discussed.

Influence of hydroxypropyl methylcellulose on drug release pattern of a gastroretentive floating drug delivery system using a 3(2) full factorial design

In the present investigation, controlled release gastroretentive floating drug delivery system of theophylline was developed employing response surface methodology. A 3(2) randomized full factorial design was developed to study the effect of formulation variables like various viscosity grades and contents of hydroxypropyl methylcellulose (HPMC) and their interactions on response variables. The floating lag time for all nine experimental trial batches were less than 2 min and floatation time of more than 12 h. Theophylline release from the polymeric matrix system followed non-Fickian anomalous transport. Multiple regression analysis revealed that both viscosity and content of HPMC had statistically significant influence on all dependent variables but the effect of these variables found to be nonlinear above certain threshold values.

In vivo assessment of novel furosemide gastro-mucoadhesive delivery system based on a kind of anion ion-exchange fiber

A novel gastro-mucoadhesive delivery system based on a kind of anion ion-exchange fiber has been developed. Furosemide (FM), which is site-specifically absorbed from the upper gastrointestinal (GI) tract, was used as model drug. A novel-modified dissolution system, which can also be called "flow through diffusion cell," was used to study the drug release from the drug fibers. The GI transit studies of the FM fiber complexes in rats and gamma imaging studies in volunteers were carried out to evaluate the gastro-mucoadhesive behavior of the fiber. The pharmacokinetic profile and parameters of the FM suspension and FM fiber in fasted and fed rats were measured, respectively. Studies on rats and volunteers provided evidence for the validity of the hypothesis that the drug fiber provided better gastro-mucoadhesive properties in vivo.

Bovine Serum Albumin–Loaded Pectinate Beads as Colonic Peptide Delivery System: Preparation and In Vitro Characterization

Objective of this study was to prepare a drug delivery system for therapeutic peptides that are degraded in the upper part of the gastrointestinal tract due to degradation activity of the enzymes. Delivering peptide to the colon in which enzymatic activity is low is next hope for absorption of these agents. Pectin, a naturally occurring water soluble polysaccharide, as a matrix for peptide delivery was studied. Degradation of pectin by the colonic enzymes makes it suitable for colon-specific delivery of drugs. Bovine serum albumin (BSA) was used as a model peptide. Calcium pectinate beads were prepared by extruding BSA-loaded pectin solution to an agitating calcium chloride solution, and gelled spheres were formed instantaneously by an ionotropic gelation reaction. The effect of several factors such as concentration of pectin, concentration of calcium chloride, and total drug loading on the pattern of drug release in the dissolution medium was studied. Prepared beads showed good resistance in the release medium. The entrapment efficiency of the beads was high (between 63% and 99%). Entrapment efficiency of BSA was reversely dependent to the amount of the drug loaded in the beads. The amount of BSA loaded on the beads affects pattern of drug release. The concentration of the pectin showed the highest impact on the rate of drug release. Presence of the pectiolytic enzymes facilitated the drug release from the beads.

A Critical Review of Gastric Retentive Controlled Drug Delivery

The promise of gastric retentive drug delivery systems has propagated numerous investigations and the formation of a number of companies. Three technologies have involved a substantial number of human clinical trials: mucoadhesion, density modification, and expansion. Standard, nondisintegrating controlled-release tablets can display significant gastric retention times, with that retention time being proportional to the calorie intake. When these data for standard tablets are factored in, gastric retention technologies do not appear to offer significant additional retention times. Although the goal remains valuable, the promise of gastric retentive drug delivery systems remains unfulfilled at this time.

A novel riboflavin gastro-mucoadhesive delivery system based on ion-exchange fiber

A novel gastro-mucoadhesive delivery system based on ion-exchange fiber has been developed. Riboflavin-5'-phosphate sodium salt (RF5P), which is site-specifically absorbed from the upper gastrointestinal tract, was used as model drug. A modified dissolution system, which can also be called 'flow through diffusion cell' (FTDC), was used to study the drug release from the drug fibers. Gastrointestinal transit studies of the RF5P fiber complexes in rats and gamma imaging study in volunteer was carried out to evaluate the gastro-retentive behavior of the fiber. The pharmacokinetic profile and parameters of riboflavin via analysis of urinary excretion of riboflavin on man were measured. Study on rat and man provide evidence for the validity of the hypothesis that the drug fiber provided good mucoadhesive properties in vivo and should therefore be of considerable interest for the development of future mucoadhesive oral drug delivery dosage forms.

Evaluation of porous carrier-based floating orlistat microspheres for gastric delivery

The purpose of this research was to prepare floating microspheres consisting of (1) calcium silicate as porous carrier; (2) orlistat, an oral anti-obesity agent; and (3) Eudragit S as polymer, by solvent evaporation method and to evaluate their gastro-retentive and controlled-release properties. The effect of various formulation and process variables on the particle morphology, micromeritic properties, in vitro floating behavior, percentage drug entrapment, and in vitro drug release was studied. The gamma scintigraphy of the optimized formulation was performed in albino rabbits to monitor the transit of floating microspheres in the gastrointestinal tract. The orlistat-loaded optimized formulation was orally administered to albino rabbits, and blood samples collected were used to determine pharmacokinetic parameters of orlistat from floating microspheres. The microspheres were found to be regular in shape and highly porous. Microsphere formulation CS4, containing 200 mg calcium silicate, showed the best floating ability (88% +/- 4% buoyancy) in simulated gastric fluid as compared with other formulations. Release pattern of orlistat in simulated gastric fluid from all floating microspheres followed Higuchi matrix model and Peppas-Korsmeyer model. Prolonged gastric residence time of over 6 hours was achieved in all rabbits for calcium silicate-based floating microspheres of orlistat. The enhanced elimination half-life observed after pharmacokinetic investigations in the present study is due to the floating nature of the designed formulations.

Bioavailability of riboflavin from a gastric retention formulation

A gastric retention formulation (GRF) made of naturally occurring carbohydrate polymers and containing riboflavin was tested in vitro for swelling and dissolution characteristics as well as in fasting dogs for gastric retention. The bioavailability of riboflavin, a drug with a limited absorption site in the upper small intestine, from the GRF was studied in fasted healthy humans and compared to an immediate release formulation. It was found that when the GRF is dried and immersed in gastric juice it swells rapidly and releases its drug content in a zero-order fashion for a period of 24 h. In vivo studies in dogs showed that a rectangular shaped GRF stayed in the stomach of fasted dogs for more than 9 h, then disintegrated and reached the colon in 24 h. Endoscopic studies in dogs showed that the GRF hydrates and swells back to about 75% of its original size in 30 min. These in vivo results correlated with in vitro results. Pharmacokinetic parameters determined from urinary excretion data from six human subjects under fasting conditions showed that bioavailability depended on the size of the GRF. The biostudy indicated that bioavailability of riboflavin from a large size GRF was more than triple that measured after administration of an immediate release formulation. Deconvolved input functions from biostudy data suggest that the large size GRF stayed in the stomach for about 15 h.

A novel calcium silicate based microspheres of repaglinide: In vivo investigations

The objective of the present investigation was to evaluate gastro-retentive performance and pharmacokinetic parameters of optimized floating microspheres (RgFMCS4) consisting of (i) calcium silicate (CS) as porous carrier; (ii) repaglinide (Rg), an oral hypoglycemic agent; and (iii) Eudragit S (ES) as polymer. The optimized formulation demonstrated favorable in-vitro-floating and drug release characteristics. The gastro-retentive behavior of this optimized formulation was compared with non-floating microspheres (RgNFM) prepared from the identical polymer. Stability test of (99m)Tc-labeled formulations were carried out using appropriate standard buffer solutions of pH 2.0, 6.8 and 7.4. The organ distribution study was performed in albino rats in order to measure labeling efficiency of the formulation with (99m)Tc. The gamma scintigraphy of the formulations was carried out in albino rabbits to monitor the transit of RgFMCS4 and RgNFM in the gastrointestinal (GI) tract. Prolonged gastric residence time (GRT) of over 6 h was achieved in all animals for calcium silicate based floating microspheres of Rg. Rg loaded optimized formulation was orally administered to albino rabbits and blood samples were used to determine pharmacokinetic parameters of Rg from floating microspheres, which were compared with pharmacokinetic parameters of the marketed tablet formulation. The relative bioavailability of Rg loaded floating microspheres was found to be increased about 3.17 times in comparison to that of the marketed tablet. The enhanced bioavailability and eliminated half-lives of Rg formulation observed in the present study are attributed to the floating nature of the designed formulations.

Gastroretentive drug delivery systems

A controlled drug delivery system with prolonged residence time in the stomach is of particular interest for drugs that i) are locally active in the stomach, ii) have an absorption window in the stomach or in the upper small intestine, iii) are unstable in the intestinal or colonic environment, or iv) exhibit low solubility at high pH values. This article gives an overview of the parameters affecting gastric emptying in humans as well as on the main concepts used to design pharmaceutical dosage forms with prolonged gastric residence times. In particular, bioadhesive, size-increasing and floating drug delivery systems are presented and their major advantages and shortcomings are discussed. Both single- and multiple-unit dosage forms are reviewed and, if available, results from in vivo trials are reported.

Gastroretentive dosage forms: Overview and special case of Helicobacter pylori

The challenge to develop efficient gastroretentive dosage forms began about 20 years ago, following the discovery of Helicobacter pylori by Warren and Marshall. In order to understand the real difficulty of increasing the gastric residence time of a dosage form, we have first summarized the important physiologic parameters, which act upon the gastric residence time. Afterwards, we have reviewed the different drug delivery systems designed until now, i.e. high-density, intragastric floating, expandable, superporous hydrogel, mucoadhesive and magnetic systems. Finally, we have focused on gastroretentive dosage forms especially designed against H. pylori, including specific targeting systems against this bacterium.

Floating drug delivery systems: a review

The purpose of writing this review on floating drug delivery systems (FDDS) was to compile the recent literature with special focus on the principal mechanism of floatation to achieve gastric retention. The recent developments of FDDS including the physiological and formulation variables affecting gastric retention, approaches to design single-unit and multiple-unit floating systems, and their classification and formulation aspects are covered in detail. This review also summarizes the in vitro techniques, in vivo studies to evaluate the performance and application of floating systems, and applications of these systems. These systems are useful to several problems encountered during the development of a pharmaceutical dosage form.

Gastroretentive delivery systems: a mini review

Various attempts have been made to develop gastroretentive delivery systems. For example, floating, swelling, mucoadhesive, and high-density systems have been developed to increase gastric retention time of the dosage forms. It is known that differences in gastric physiology, such as, gastric pH, and motility exhibit both intra- as well as inter-subject variability demonstrating significant impact on gastric retention time and drug delivery behavior. Nevertheless, some floating devices have shown promising results. In this paper, the gastric physiology and the reported intragastric delivery systems have briefly been presented.

Gastroretentive Delivery Systems: Hollow Beads

The objective of this study was to develop a floatable multiparticulate system with potential for intragastric sustained drug delivery. Cross-linked beads were made by using calcium and low methoxylated pectin (LMP), which is an anionic polysaccharide, and calcium, LMP, and sodium alginate. Beads were dried separately in an air convection type oven at 40 degrees C for 6 hours and in a freeze dryer to evaluate the changes in bead characteristics due to process variability. Riboflavin (B-2), tetracycline (TCN), and Methotrexate (MTX) were used as model drugs for encapsulation. Ionic and nonionic excipients were added to study their effects on the release profiles of the beads. The presence of noncross linking agents in low amounts (less than 2%) did not significantly interfere with release kinetics. For an amphoteric drug like TCN, which has pH dependent solubility, three different pHs (1.5, 5.0, and 8.0) of cross-linking media were used to evaluate the effects of pH on the drug entrapment capacity of the beads. As anticipated, highest entrapment was possible when cross-linking media pH coincided with least drug solubility. Evaluation of the drying process demonstrated that the freeze-dried beads remained buoyant over 12 hours in United States Pharmacopeia (USP) hydrochloride buffer at pH 1.5, whereas the air-dried beads remained submerged throughout the release study. Confocal laser microscopy revealed the presence of air-filled hollow spaces inside the freeze dried beads, which was responsible for the flotation property of the beads. However, the release kinetics from freeze dried beads was independent of hydrodynamic conditions. Calcium-pectinate-alginate beads released their contents at much faster rates than did calcium-pectinate beads (100% in 10 hours vs. 50% in 10 hours). It appears that the nature of cross-linking, drying method, drug solubility, and production approach are all important and provide the opportunity and potential for development of a gastroretentive drug delivery system.

Floating matrix tablets based on low density foam powder: effects of formulation and processing parameters on drug release

The aim of this study was to develop and physicochemically characterize single unit, floating controlled drug delivery systems consisting of (i). polypropylene foam powder, (ii). matrix-forming polymer(s), (iii). drug, and (iv). filler (optional). The highly porous foam powder provided low density and, thus, excellent in vitro floating behavior of the tablets. All foam powder-containing tablets remained floating for at least 8 h in 0.1 N HCl at 37 degrees C. Different types of matrix-forming polymers were studied: hydroxypropyl methylcellulose (HPMC), polyacrylates, sodium alginate, corn starch, carrageenan, gum guar and gum arabic. The tablets eroded upon contact with the release medium, and the relative importance of drug diffusion, polymer swelling and tablet erosion for the resulting release patterns varied significantly with the type of matrix former. The release rate could effectively be modified by varying the "matrix-forming polymer/foam powder" ratio, the initial drug loading, the tablet geometry (radius and height), the type of matrix-forming polymer, the use of polymer blends and the addition of water-soluble or water-insoluble fillers (such as lactose or microcrystalline cellulose). The floating behavior of the low density drug delivery systems could successfully be combined with accurate control of the drug release patterns.

Floating microparticles based on low density foam powder

The aim of this study was to develop a novel multiparticulate gastroretentive drug delivery system and to demonstrate its performance in vitro. Floating microparticles consisting of (i) polypropylene foam powder; (ii) verapamil HCl as model drug; and (iii) Eudragit RS, ethylcellulose (EC) or polymethyl methacrylate (PMMA) as polymers were prepared with an O/W solvent evaporation method. The effect of various formulation and processing parameters on the internal and external particle morphology, drug loading, in vitro floating behavior, in vitro drug release kinetics, particle size distribution and physical state of the incorporated drug was studied. The microparticles were irregular in shape and highly porous. The drug encapsulation efficiency was high and almost independent of the theoretical loading. Encapsulation efficiencies close to 100% could be achieved by varying either the ratio 'amount of ingredients: volume of the organic phase' or the relative amount of polymer. In all cases, good in vitro floating behavior was observed. The release rate increased with increasing drug loading and with decreasing polymer amounts. The type of polymer significantly affected the drug release rate, which increased in the following rank order: PMMA<EC<Eudragit RS. A broad spectrum of release patterns could be obtained with the investigated formulations. In contrast, the effect of the volume of the aqueous phase on drug release was not very pronounced. The size of the microparticles was almost independent of the drug loading, but strongly depended on the amount of polymer. The drug was partly dissolved and partly in the amorphous form distributed throughout the system.

Ion-exchange resins: carrying drug delivery forward

Ion-exchange resins (IER), or ionic polymer networks, have received considerable attention from pharmaceutical scientists because of their versatile properties as drug-delivery vehicles. In the past few years, IER have been extensively studied in the development of novel drug-delivery systems (DDSs) and other biomedical applications. Some of the DDSs containing IER have been introduced into the market. In this review, the applications of IER in drug delivery research are discussed.

Effect of resin surface charge on gastric mucoadhesion and residence of cholestyramine

Previous studies performed on excised gastric tissue and in healthy volunteers revealed that the ion exchange resin, cholestyramine, exhibits mucoadherent behaviour. This study was designed to elucidate whether surface charge affected this behaviour. Gamma scintigraphy was performed on fasted normal subjects following oral administration of cholestyramine or the cationic exchanger Amberlite(R) IRP-69, either uncoated or polymer-coated to mask their charge. Subjects were fed after 4 h. The initial gastric emptying of all formulations was similar (T(50) values (mean+/-S.E.M.): cholestyramine=85.86+/-9.16 min; IRP-69=76.09+/-9.23 min; polymer-coated cholestyramine=72.0+/-12.64 min; polymer-coated IRP-69=70.25+/-10.57 min: P=0.724). However, after 3 h the emptying pattern of cholestyramine was slower than that of IRP-69. This resulted in greater retention times than IRP-69 (AUC(0-6) values (relative units)=15,200+/-1093 versus 9452+/-811; cholestyramine versus IRP-69: P=0.0004). This effect was reduced by polymer-coating the cholestyramine. Serial images showed that cholestyramine was trapped in the oropharyngeal region and subsequently displaced by the meal, resulting in higher levels of activity remaining at 6 h. Thus, cholestyramine exhibited prolonged gastric residence via mucoadhesion and was distributed throughout the stomach. The surface charge of the resin was found to have a contributory role. These materials may have potential for the delivery of drugs in the topical treatment of the gastric mucosa, for example in the eradication of Helicobacter pylori.

Effect of interparticulate interaction on release kinetics of microsphere ensembles

The release kinetics of microsphere ensembles is complicated by the mutual influence of the microspheres which are entrapped in small compartments such as body cavities. This work focused on the effect of interparticulate interaction on the release kinetics of microsphere ensembles with limited spreading. Experiments and finite element modeling were conducted to investigate diffusional drug release from a single sphere, a monolayer, and multiple layers of microspheres. Poly(methyl methacrylate-co-methacrylic acid) (P(MMA/MAA)) microspheres and azidothymidine (AZT) were used in the experiments. The order of the release rate of AZT from various microsphere populations was observed to be single sphere > monolayer > multiple layers. This evidenced the importance of interparticulate interaction. The finite element simulations elucidated the influence of various factors on the release kinetics of microsphere ensembles including the separation distance, location of the spheres, and the drug accumulation in the medium. Calibration of overall release kinetics for the neighboring effect was proposed on the basis of the spreading factor. Overall release profiles of microsphere ensembles were predicted using the release profiles of individual microspheres at various locations.