Development of sensor elements to control drug release from capsular drug delivery systems

The objective of this study was to develop a capsular drug delivery system, which releases the drug when a sensor element is activated by gastrointestinal fluids. The sensor element consists of a microswitch and a control membrane. After disintegration or dissolution of the control membrane the gastrointestinal fluid switches on an electric circuit. Via a gas producing cell the drug reservoir of the capsule is emptied within 6 min. In vitro experiments with pH-sensitive polymethacrylic sensor membranes (Eudragit S 100) show that prednisolone dihydrogenphosphate is released within a few minutes when the capsule is transferred from gastric juice to artificial intestinal fluid of pH 6.8. Experiments with sensor elements prove that the membrane thickness influences the response time of the sensor. When 32 microm membranes are used, the electric circuit is switched on with a delay of about 70-80 min at pH 6.8. The developed systems are intended to be used as pump systems to deliver drugs into specific areas of the gastrointestinal (GI) tract.