Modified push-pull osmotic system for simultaneous delivery of theophylline and salbutamol: development and in vitro characterization

An oral osmotic system which can deliver theophylline and salbutamol sulphate simultaneously for extended period of time was developed and characterized in a view to reduce the problems associated with the multidrug therapy of asthma. Simple controlled porosity osmotic pump contained both drugs (in freely soluble form) did not provide satisfactory extended release of theophylline. A modified two-layered, push-pull osmotic system was developed by using the basic designs of various oral osmotic pumps, such as controlled porosity osmotic pump (CPOP), elementary osmotic pump (EOP) and push-pull osmotic pump (PPOP). Scanning electron microscopy of cellulose acetate coating membrane after dissolution revealed that 25% (w/w) of sorbitol can be used as an optimized concentration of pore forming agent with 25% (w/w) of plasticizer, which was kept constant. Formulations were initially developed for theophylline and the release was optimized by using two different soluble forms of theophylline with varying amount of hydrophilic polymer mixture in upper layer and polyethylene oxide (expandable hydrogel) in lower layer. Further, the release of salbutamol sulphate was optimized by keeping the drug in upper or lower layer or both layers. In vitro release studies showed satisfactory controlled release profiles of both drugs. The release profiles of both drug statistically compared with respective marketed controlled release formulations. An optimized system was selected to study the effect of concentration of pore forming agent and orifice diameter on the release of both drugs.