The objective of this investigation was to compare the single-dose and steady-state pharmacokinetic profiles of Dilacor XR to Cardizem CD. The study enrolled 24 healthy males and was divided into three parts: a single intravenous 25-mg bolus dose of diltiazem HC1 (Cardizem Injectable) followed by a two-way crossover comparison of single and multiple once-daily 240-mg oral doses of Dilacor XR and Cardizem CD. Plasma samples were analyzed for diltiazem using a specific and sensitive HPLC assay. Statistical analysis and deconvolution were performed on the data. A 1− and 3-hour lag time in diltiazem absorption was noted following the administration of Dilacor XR and Cardizem CD, respectively. Statistically significant differences were noted in mean single- and multiple-dosetmaxvalues with Cardizem CD taking approximately twice as long as Dilacor XR to reach Cmax. Dilacor XR was equivalent to Cardizem CD with respect to AUC(0−X)and Cmax. Equivalent minimum and average steady-state plasma diltiazem concentrations were noted after multiple-dose administration. Deconvolution of the single-dose data also showed similar mean bioavailabilities for the respective formulations but revealed dissimilarities in each product's absorption profile that may reflect observed differences in absorption lag time andtmax.