Sustained-release dosage form of nitrofurantoin. Part 1. Preparation of microcapsules and in vitro release kinetics

Polymer-coated microparticles for the sustained release of nitrofurantoin

Suspensions of nitrofurantoin (NTF) microparticles for controlled release were investigated in this study. The microparticles were enteric coated with various combinations of the two polymers, cellulose acetate phthalate/cellulose acetate butyrate (CAP/CAB) by a modified solvent evaporation method. Ratios of NTF to the two polymers (NTF/CAP/CAB) ranged from 1.0:1.6:0.4,1.0:1.0:1.0,1.0: 0.4:1.6 to 1.0:0.0:2.0. The encapsulation efficiency, percentage yield, determined by comparing the final mass of the microparticles with the initial mass of the ingredients used, distribution of particle size and the in-vitro dissolution profiles of the microparticles were determined. Based on light photographs for the evaluation of the microparticle morphology, the drug crystals appeared to be encapsulated sufficiently by the enteric polymers. In our study, the microparticles enteric coated with CAP/CAB in the ratio of 0.4:1.6 displayed the most satisfactory in-vitro release profile (reduced release in the simulated gastric fluid and sustained release in the simulated intestinal fluid). Thus, microparticles with NTF/CAP/CAB in the ratio of 1.0:0.4:1.6 were formulated into a suspension for further bioavailability and ulcerogenicity studies in Sprague-Dawley rats, with the suspension of NTF crystals as a control. The bioavailability study was carried out in eight rats fed with either the free NTF or the corresponding microparticles in a cross-over design. The ulcerogenicity study was carried out in three groups of six rats each: one group received no drug treatment; the control group was treated with free NTF; and the third group was treated with enteric-coated NTF microparticles. The bioavailability of NTF from the microparticles was comparable with the control. More importantly, there was notably less ulceration of the gastric mucosa observed after dosing with the microparticle suspension compared with that after the administration of the control suspension.

The effects of some physico-chemical factors and pharmaceutical excipients on the bioavailability of nitrofurantoin oily and aqueous suspensions in rats

The effects of some physico-chemical factors and various excipients, i.e., sucrose, aluminum stearate, hydrogenated castor oil, Cab-o-sil, and lecithin, either alone or in combination, from suspensions in fractionated coconut oil and distilled water have been investigated. In vitro drug release studies were performed according to the flask-stirrer method. In addition to adsorption and solubility studies, determination of partition coefficients and rheological measurements have been carried out. The experimental design was based on an 8x8 latin square using rats as the test animals. The results of the study showed that the rate and extent of absorption of nitrofurantoin are decreased significantly by the use of an oil' rather than an aqueous vehicle. In vitro drug release data showed some correlation with in vivo parameters, and also with the apparent viscosity of the vehicles. However, no correlation was detectable between in vivo parameters and the apparent viscosity of the vehicles.

Sustained-release microcapsules of nitrofurantoin and amoxicillin; preparation, in-vitro release rate, kinetic and micromeritic studies

In this work, nitrofurantoin and amoxicillin trihydrate microcapsules were prepared by complex coacervation at pH 3.5 using carboxymethylcellulose-gelatin at a weight ratio of 3:7. Release rates were studied as a function of core:wall ratios of microcapsules. Dissolution tests of microcapsules and their tabletted microcapsules were studied in artificial gastric and intestinal media without enzyme using the USP XXII basket method. Release rates were examined kinetically and the ideal kinetic models were estimated for drug release. In addition, the micromeritics of these microcapsules were investigated. In order to standardize the drug powder and the microcapsule product for industrial application, the micromeritic properties of microcapsules were studied by determining their bulk volume and weight, tapping volume and weight, fluidity, angle of repose, weight deviation, particle size distribution, density and porosity. Hausner ratio and consolidation index were also calculated to understand flowability rates of microcapsules when tableting or filling into gelatin capsules. The results indicated that the nitrofurantoin microcapsules need appropriate glidant but the amoxicillin trihydrate microcapsules did not. Moreover, it was observed that the microencapsulation changed the micromeritic properties of the drugs significantly.

Chitosan/calcium alginate microcapsules for intestinal delivery of nitrofurantoin

A new sustained-release dosage form of nitrofurantoin (NF) as microcapsules has been prepared by a mild chitosan/calcium alginate microencapsulation process. These microcapsules have been prepared by adding, dropwise, a solution of sodium alginate containing NF into a chitosan-CaCl(2) system. About 70-80% of the drug is released into phosphate buffer, pH = 7.4 within 6 h. Drug release into the gastric medium is found to be relatively slow compared to that into the intestinal medium. From scanning electron microscopic studies, it appears that the chitosan modifies the NF-alginate microspheres. These findings suggest the possibility of modifying the formulation to obtain the controlled release of NF in an oral sustained-delivery system.

3(3) factorial design-based optimization of the formulation of nitrofurantoin microcapsules

A microcapsule form of nitrofurantoin was prepared by a simple coacervation method with carboxymethylcellulose and aluminium sulfate. 3(3) factorial design was performed for three independent variables, namely, the particle size of the drug, the size of the microcapsules and the pH of the dissolution medium. The dissolution tests with the formulated microcapsules were carried out according to the United States Pharmacopeia XXII rotating basket method at pH 1.2, 5, and 7.5, which represent the pH of gastrointestinal fluids. Release data were examined kinetically and the ideal kinetic models were estimated and t(63.2) values obtained from RRSBW distribution were used in the factorial design experiment. The influence of the independent variables on the dissolution of nitrofurantoin microcapsules could be expressed as the pH of the dissolution medium > particle size of the microcapsule > particle size of nitrofurantoin. The other aim of this study was to evaluate microcapsule formulation in terms of the United States Pharmacopeia criteria with a minimum of experiments. Our findings suggest that dosage forms which comply with the pharmacopoeia criteria for dissolution can be prepared and selected by factorial design.