Natural Polymer Hydrophilic Matrix: Influencing Drug Release Factors

Tailoring of drug delivery of 5-fluorouracil to the colon via a mixed film coated unit system

The study was carried out to establish the effectiveness of a mixed film composed of ethylcellulose/Eudragit S100 for colonic delivery of 5-flourouracil (5-FU). Tablets cores containing 5-FU were prepared by direct compression method by coating at different levels (2-9%, m/m) with a non-aqueous solution containing ethylcellulose/Eudragit S100. Coated tablets were studied for the in vitro release of 5-FU and the samples were analyzed spectrophotometrically at 266 nm. Drug release from coated systems depended on the thickness of the mixed film and the composition of the core. Channel formation was initiated in the coat by dissolution of the Eudragit S100 fraction at higher pH in the colonic region. The release was found to be higher in tablets containing Avicel as filler owing to its wicking action compared to that from lactose containing cores. Furthermore, batches containing superdisintegrant (1%, m/m Cross-PVP) along with Avicel in the core released approximately 81.1% drug during the colonic transit time. Kinetic studies indicated that all the formulations followed first-order release kinetics. The developed delivery system will expectedly deliver the drug to the colon.

Sustain-release of various drugs from leucaena leucocephala polysaccharide

This study examines the sustained release behavior of both water-soluble (acetaminophen, caffeine, theophylline and salicylic acid) and water-insoluble (indomethacin) drugs from Leucaena leucocephala seed Gum isolated from Leucaena leucocephala kernel powder. It further investigates the effect of incorporation of diluents like microcrystalline cellulose and lactose on release of caffeine and partial cross-linking of the gum (polysaccharide) on release of acetaminophen. Applying exponential equation, the mechanism of release of soluble drugs was found to be anomalous. The insoluble drug showed near case II or zero-order release mechanism. The rate of release was in the decreasing order of caffeine, acetaminophen, theophylline, salicylic acid and indomethacin. An increase in release kinetics of drug was observed on blending with diluents. However, the rate of release varied with type and amount of blend in the matrix. The mechanism of release due to effect of diluents was found to be anomalous. The rate of release of drug decreased on partial cross-linking and the mechanism of release was found to be super case II.

Use of a moist granulation technique (MGT) to develop controlled-release dosage forms of acetaminophen

The moist granulation technique (MGT), which involves agglomeration and moisture absorption, has only been applied to immediate-release dosage forms. Our results indicate that MGT appears to be applicable in developing a controlled-release formulation. A small amount of granulating fluid (water) was added to a powder blend to activate a dry binder (such as polyvinylpyrrolidone [PVP] at 2% and 3.6%) and to facilitate agglomeration. Then, a moisture-absorbing material (microcrystalline cellulose [MCC]) was added to absorb any excess moisture. By adding MCC in this way, a drying step was not necessary. Acetaminophen (APAP) was the model drug, with diluents lactose FastFlo and dicalcium phosphate. Hydroxypropylcellulose (HPC) was used as the controlled-release agent. The MGT was compared to conventional wet granulation (WG) and direct compression (DC) processing methods. The results indicate that MGT appears to be applicable in developing a controlled-release formulation. Particle size distribution of MGT and WG batches containing 3.6% PVP is similar.

Natural gums and modified natural gums as sustained-release carriers

Although natural gums and their derivatives are used widely in pharmaceutical dosage forms, their use as biodegradable polymeric materials to deliver bioactive agents has been hampered by the synthetic materials. These natural polysaccharides do hold advantages over the synthetic polymers, generally because they are nontoxic, less expensive, and freely available. Natural gums can also be modified to have tailor-made materials for drug delivery systems and thus can compete with the synthetic biodegradable excipients available in the market. In this review, recent developments in the area of natural gums and their derivatives as carriers in the sustained release of drugs are explored.

Sustained release microspheres of metoclopramide using poly(D,L-lactide-co-glycolide) copolymers

Metoclopramide was encapsulated with poly(D,L-lactide co glycolide) copolymers of different molecular weights using the emulsification/solvent evaporation technique. These polymers included poly(D,L-lactide-co-glycolide) 50:50 with inherent viscosity (i.v.) 0.2, and average molecular weight 8000, poly(D,L-lactide-co-glycolide) 50:50 with i.v. 0.8 and average molecular weight 98000 and poly(D,L-lactide-co-glycolide) 85:15 with i.v. 1.4 and average molecular weight 220000. The effect of the polymers' molecular weights as well as the polymer-to-drug ratios on the yield, the particle size distribution, and the drug content of the microspheres was investigated. The release rate of the drug was studied for 96 h in a phosphate buffer of pH 7.4. The study also investigated the effect of the new poly(lactide-co-glycolide)-H series on the characteristics of the prepared microspheres. Data revealed that a higher yield was obtained with polymers of lower molecular weights. A lower yield was also obtained with increasing the drug-to-polymer ratios for all the investigated polymers. The drug content of the microspheres was lower than expected, ranging from 49-85%, which suggested a chemical interaction between the drug and the polymers, as proved by differential scanning calorimetry (DSC) and infra red (IR) studies. A higher interaction was obtained with the H-series of the copolymers. The release of the drug mainly followed zero order kinetics on increasing either the polymers' molecular weights or the polymer-to-drug ratios. Diffusion kinetics was observed only with those batches prepared with low polymer-to-drug ratios. The release rate was a function of both the polymers' molecular weights and the drug-to-polymer ratios.

Tablet and capsule hydrophilic matrices based on heterodisperse polysaccharides having porosity-independent in vitro release profiles

The purpose of the study was to investigate the release-controlling action of a swellable hydrophilic material based on heterodisperse polysaccharides (HP) in relation to the initial pore structure of the formulations. HP-based granules were produced under carefully controlled conditions and compacted into matrix tablets having equivalent tablet thickness. Quantification of pore structure using mercury porosimetry showed that the tablets had substantially different pore volumes and pore size distributions. Dissolution studies demonstrated that release of a water-soluble model compound, benzamide, from swollen matrices was affected neither by total porosity nor median pore diameter of the initial dry matrix. To extend the concept of porosity-independent release further, HP-based formulations containing either diclofenac sodium or propranolol HCl were contained within hard gelatin capsules in the form of uncompacted granules. This produced a dosage form with a high intraparticulate porosity in the dry state. Equivalent weights of the same formulations were also compacted into tablets. The in vitro release profiles from matrix tablets compacted from any of the formulations did not differ significantly from release profiles obtained when the same materials were contained uncompacted in hard gelatin capsules.