Assessment of bioavailability of experimental controlled release microcapsules of nifedipine

Experimental controlled release nifedipine microcapsules composed of ethylcellulose and eudragit RL were explored for the assessment of bioavailability on rabbit. The pharmacokinetic parameters were compared between the formulations and with the pure drug material. A statistically significant difference between the formulations was noticed in the parameters, K, T1/2, AUC (0-->infinity), MRT and bioavailability but not in Vd, Cmax and Tmax and in each case a highly significant difference was observed with reference drug material. Controlled release absorption profiles in vivo were observed from the experimental microcapsules as revealed by the Wagner-Nelson method. The absorption lag time, absorption rate constant, and absorption half life were calculated by using the back projection method of residuals. A good correlation demonstrated between in vivo absorption and in vitro release data for both the products merits specific attention. There was no loss in bioavailability of the experimental ethylcellulose microcapsule (drug content 75.8%), even though nifedipine undergoes extensive first pass metabolism.