The relative bioavailability of two marketed controlled release diltiazem dosage forms at steady state in healthy volunteers.

This study was conducted to determine the relative bioavailability of Dilacor XR capsules compared to Cardizem CD capsules at both low (180 mg d-1) and high (540 mg d-1) dose levels. Trough and serial plasma samples were obtained and pharmacokinetic parameters were calculated from the steady state concentration-time profiles. Mean steady state plasma diltiazem concentrations (AUCss(0-24)) of Dilacor XR were 19% and 26% lower than those of Cardizem CD for the 180 mg d-1 and 540 mg d-1 dose levels, respectively. In addition, Dilacor XR had lower mean Cmax,ss, Tmax,ss, Cmin,ss, and trough values than Cardizem CD with percentage differences ranging from 17% to 29%. The variability (%CV) in the data from the Dilacor XR treatments was higher for each calculated pharmacokinetic parameter compared to the Cardizem CD treatments. The %CV for Dilacor XR ranged from 34% to 104% while the %CV for Cardizem CD ranged from 21% to 49%. From these results, it may be concluded that Dilacor XR is not bioequivalent to Cardizem CD at steady state doses of 180 mg d-1 and 540 mg d-1.