(198j) Experimental Investigations to Study the Release of Drug and Excipients from Bilayer Osmotic Tablets

Controlled drug delivery systems through the sustained release of drugs enable the drug concentration to remain within the therapeutic range for a long time, thus increasing the effectiveness of drugs. One of the most successful delivery system is the oral osmotic delivery system as the delivery of drug is independent of external conditions such as pH and hydrodynamic condition.

Here, we present experiments performed with bilayer osmotic tablets in which the upper layer consists of the drug and polymer, and the lower layer consists of the osmotic agent and a swellable polymer. Model (inert) particles were used instead of drug particles to understand the influence of various factors such as orifice size and coating thickness on the extrusion of the model drug particles. We designed a setup to extract the extrudate during the extrusion process and the concentration of the individual components in the extrudate was measured and related to the relative composition of the polymer, osmotic agent and drug particles in the drug layer. Next, we compared the measurements with predictions of a mathematical model that accounts for the details of the drug delivery process, namely, solvent imbibition due to osmotic pressure gradient, hydration of the drug layer, swelling of the sweller layer, build-up of hydrostatic pressure and extrusion of the extrudate through the orifice. The results show a good agreement between measurements and model predictions suggesting that the model captures well all the key processes involved in drug release process.