Design and Evaluation of Rectal Suppositories of Carvedilol

Abstract

Carvedilol (non-cardio selective b-blocker) is an antihypertensive used in management of hypertension, angina pectoris and heart failure.  But its oral bioavailability is about 25-35% only due to significant degree of first pass metabolism.  It has gastrointestinal side effects such as diarrhea, gastric pain and irritation.  Hence, rectal suppositories of carvedilol were developed by using different water-soluble polymeric bases like gelatin and agar-agar using propylene glycol as plasticizer. The gelatin suppositories were disintegrating/dissolving type while gelatin–agar based suppositories were non-disintegrating/non-melting. All the formulations were evaluated for various physical parameters like weight variation,  drug content uniformity, liquefaction time, micro-melting range, in vitro dissolution, short-term stability and drug-excipient interaction (FTIR).  The mechanism of drug release was diffusion controlled and follows first order kinetics in majority of cases. The results suggested that when gelatin is replaced up to 25% w/w with agar, liquefaction time and drug release were not appreciably affected; higher proportions of agar exhibited incomplete and slow release.  Stability studies conducted at 25±3º C and 60±5% relative humidity for three months indicated that the formulations were stable in the drug-content and in vitro drug release rate (p<0.05).