Preparation and in-vitro evaluation of sustained release theophylline micro-spheres

ABSTRACT

A modified emulsion-solvent evaporation technique was utilized to prepare sustained release microspheres containing theophylline [TH]. Two polymers were used for microspheres preparation, namely cellulose propionate [CP] and ethyl cellulose [EC]. The two polymers were used at 11, 21, and 32 [drug - polymer ratios]. The prepared microspheres were evaluated for their total recovery, drug loading, particle size distribution, surface morphology, drug content and drug release rate characteristics. The results have shown that, the total percentages drug recovery reached 96, 97.7and 90.3 for cellulose propionate at 11, 21 and 32 [drug -polymer ratios], and that of drug loading reached 89, 90, and 92 respectively. However, with ethyl cellulose, the total% drug recovery reached 99, 100, and 94 using the same drug -polymer ratios, and the total% drug loading reached, 85, 90, and 90 respectively. The results obtained have shown a significant complete recovery with an excellent drug loading and thus the efficiency of the procedure utilized to encapsulate the drug. The drug release characteristics from the prepared microspheres in simulated gastric fluid [pH 1.2] and phosphate buffer [pH 6.8] were compared with commercial sustained release capsules of theophylline [Theo SR 100]. Results have revealed that, the release rate of theophylline was influenced by the type of polymer, microsphere size, pH as well as drug to polymer ratio. The decrease in particle size of the prepared microspheres led to increase in the release rate. However, the prepared microspheres showed more retarded release of theophylline than from the tested commercial product. Moreover, ethyl cellulose as a polymer was more effective for sustained effect. The release data were fitted to Peppas diffusion equation. Results have indicated that the release pattern of theophylline followed zero-order kinetics