Formation and in-vitro evaluation of theophylline-loaded poly(methyl methacrylate) microspheres.

Theophylline-loaded poly(methyl methacrylate) (PMM) microspheres were prepared by the solvent evaporation method. Increasing the drug to polymer ratio increased both the mean particle size of the microspheres and the release rate. Polyethylene glycol (PEG) 4000 was used to improve the release rate of theophylline from the microspheres. No marked effect was observed on particle size distribution of the microspheres as a function of PEG concentration but there was a pronounced effect on drug release. The different particle sizes of microspheres prepared from the same drug to polymer ratio showed no significant difference in drug content, indicating that the ratio between theophylline and PMM remained practically constant regardless of the size of microspheres. Release characteristics of the microspheres were influenced by drug to polymer ratio, the amount of PEG incorporated and the particle size of microspheres. The release rate was slightly higher in simulated gastric fluid than in simulated intestinal fluid. The release profiles of the drug were modified by mixing microspheres of different formulations in different ratios.