Effect of size and dosage strength on the bioavailability of two diltiazem formulations during repeated administrations in humans.

In angina pectoris, diltiazem is usually prescribed as two 60 mg tablets in the morning and two 60 mg tablets in the evening. In the course of the pharmaceutical development of this drug, it was therefore planned to study an experimental formulation containing 120 mg of diltiazem. On the basis of dissolution tests in vitro, a bioavailability study was initiated to compare the 120 mg experimental formulation to the standard 60 mg tablet. The study was conducted in 12 healthy volunteers who received the 2 treatments (one 120 mg tablet bid for 7 days versus two 60 mg standard tablets bid for 7 days) according to a cross-over design. Blood and urine samples were analysed by HPLC method with a UV spectrophotometric detection (sensitivity: 5 ng/ml). Analysis of variance did not show any significant difference between the two formulations for the following parameters: maximum plasma levels observed at steady-state, area under the curves and unchanged urinary diltiazem. From these results the extent of absorption of the 120 mg experimental formulation can be considered as bioequivalent to the administration of 2 tablets of the 60 mg commercially available diltiazem formulation. The time to peak, however, was delayed in 75% of the subjects with the 120 mg diltiazem tablet, showing that the surface area of the pharmaceutical preparation is of primary importance for drug dissolution and rate of absorption.