In vitro modified release of acyclovir from ethyl cellulose microspheres

The aim of this study was to demonstrate a sustained-release microparticula te dosage form for acyclovir via an in vitro study. Ethyl cellulose was sel ected as a model encapsulation material. All of the microspheres were prepa red by an oil-in-water solvent evaporation technique. A 2(3) full factorial experiment was applied to study the effects of the viscosity of polymer, p olymer/drug ratio, and polymer concentration on the drug encapsulation effi ciency and the dissolution characteristics. The encapsulation efficiency of acyclovir in microspheres was in the range of 20.0-56.6%. Increase in the viscosity of ethyl cellulose and the ratio of CH2Cl2/ethyl cellulose increa sed drug encapsulation efficiency. The drug continuously released from micr ospheres for at least 12 h, and the release rate depended on the pH of the release medium. The sustained release characteristic was more prominent in the simulated intestine fluid than in the simulated gastric fluid. A faster release of drug was observed when a high viscosity polymer was used. The d ecomposition of acyclovir significantly decreased when encapsulated by ethy l cellulose, especially when stored at 37 and 50 degreesC.