Development and evaluation of a floating multiparticulate gastroretentive system for modified release of AZT.

The aim of this study was to develop and evaluate a floating multiparticulate gastroretentive system for the modified release of zidovudine (AZT). AZT was used as a model drug water-soluble at therapeutic doses. The floating gastroretentive system was obtained by co-precipitation, after solvent diffusion and evaporation. The proposed system was evaluated in vitro for particle morphology, lag time and floating time, loading rate, release profile, and the release kinetic of AZT release. AZT's physico-chemical characteristics were evaluated by differential scanning calorimetry (DSC), X-ray diffraction (XDR) and infrared spectroscopy (IR). The particles obtained were sphere-shaped, hollow, and had porous walls. The floating was immediate, and floating time was higher than 12 h. The loading rate was 34.0 ± 9.0%. The system obtained had an extended release. DSC and XDR results showed a modification in AZT's solid state. IR spectroscopy revealed that the chemical structure of the AZT was unchanged. The hollow microballoons presented gastroretentive, floating, and extended-release properties.

[Study on index for formulation optimization of sustained or controlled released dosage forms].

Release in vitro is one of the indexes for quality control of solid dosage forms. It is not only the important indexes for evaluation of bioequivalence, also the important parameter of formulation optimization, study of the stability and quality control within producing of sustained or controlled release dosage forms. The review is the study on index for formulation optimization of sustained or controlled released dosege forms in China since 1999, including the application of similarity factor and deviation.

[Sustained-release pellet of vasodilators--basic experiment].

We examined the efficacy of slow-release, and prolonged diffusion silicone pellets mixed with papaverine hydrochloride in the treatment of cerebral vasospasms following subarachnoid hemorrhage. In addition the diffusion of the other vasodilating agents (diltiazem and nicardipine) into the saline solution using the same silicone materials was also investigated. Papaverine hydrochloride was either packed in silicone tubes (packed type) or polymerized with silicone elastomer, Silastic MDX-4-4210 (solid type). The solid type pellet is cylindrical-(diameter 3 mm, length 30 mm) and contains 40 w/v% of pure powder of papaverine. The amount of the delivered drug was measured for 5 weeks at 37 degrees C and at room temperature. The diffusion rate of the solid type pellet was about 5 times higher than that of the packed one. The diffusion rates of both types of pellets were about 10 times higher at 37 degrees C than at room temperature. The cummulative amount of the delivered drug from the solid type pellet was 37.1% of the initial packed volume at 37 degrees C in the first 3 weeks. The diffusion of diltiazem and nicardipine which were polymerized 30 w/v% in silicone elastomer was observed for 3 weeks at 37 degrees C only in solid type pellet form. The diffusion rate was measured under the condition of either continuous shaking or standing. The results showed the same diffusion rates for diltiazem and nicardipine, with no difference in diffusion rate between the "shaking" and "standing" groups. The diffusion rate showed inverse exponential curves, and was 5-20 X 10(-5)/day/mm2 of initial volume until 5 days.(ABSTRACT TRUNCATED AT 250 WORDS)