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 1:1, 2:1, and 3:2 (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 1:1, 2:1 and 3:2 (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.