Preparation and evaluation of a sustained-release suspension containing theophylline microcapsules

A great effort has been devoted to the preparation of sustained-release formulations of theophylline to prevent large fluctuations of serum concentration and increasing the therapeutic efficacy followed by patient compliance. In the present study, microcapsules of theophylline with ethyl cellulose (EC) were prepared by emulsion-solvent evaporation method in different polymer to drug ratios. Size, morphology, drug loading and release behavior of microcapsules were also studied. Microcapsules were then formulated into suspensions to provide an oral liquid dosage form for drug and resulting suspensions were examined for stability and release characteristics in various storage times. Results showed that microcapsules prepared in drug to polymer ratio 1:1.4 by emulsifying polymer solution in liquid paraffin presented the sustained-release properties which met the United States Pharmacopeia (USP) (2007) requirements (t(50%) and t(80%) of these microparticles were 150 and 360 min, respectively). The suspensions prepared by these microcapsules were also stable in the study period and their release profiles were consistent to the original microcapsules. The results allow for the conclusion that the formulated suspension can be used as a sustained-release formulation for theophylline in treatment of obstructive pulmonary disorders.