Floating Properties and Release Characteristics of Hollow Microspheres of Acyclovir

Abstract

Acyclovir, a selective antiherpes virus agent, was loaded in the hollow microspheres to improve bioavailability and patient compliance by prolonging the residence time in the gastrointestinal tract. The hollow microspheres of acyclovir were prepared by solvent evaporation diffusion method using Eudragit S 100 as a controlled polymer. We found that the process conditions that provided the high % yield of the hollow microspheres were the use of 5:8:2 of dichloromethane: ethanol: isopropanol as a solvent system and stirring at 300 rpm for 60 min. The size of the microspheres prepared from different ratios of acyclovir and Eudragit S 100 was 159–218 μm. When the drug-to-polymer ratio was increased, the size and percent drug content increased. The highest percent drug entrapment was obtained at the ratio of 600 mg acyclovir: 1 g Eudragit S 100. The hollow microspheres tended to float over 0.1 M hydrochloric acid containing 0.02% Tween 20 solution for 24 hr. The rate of acyclovir released from the microspheres was generally low in simulated gastric fluid without enzyme due to the low permeability of the polymer. However, in phosphate buffer pH 6.8, the drug release increased as the drug load increased due to the swelling property of the polymer. In simulated intestinal fluids without enzymes, the polymer completely dissolved resulting in instant release of the drug in this medium.