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 HCl (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-dose t(max) values with Cardizem CD taking approximately twice as long as Dilacor XR to reach C(max). Dilacor XR was equivalent to Cardizem CD with respect to AUC((0--infty infinity)) and C(max). 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 and t(max).