Pharmacokinetics of diltiazem after intravenous and oral administration

The kinetic profile of diltiazem, a novel calcium antagonist, was studied in 12 volunteers following oral (60 mg) and intravenous (15 mg) administration. After i.v. administration biphasic elimination was observed, with a distribution half-life of 0.3 +/- 0.2 h and an elimination half-life of 3.1 +/- 1.0 h; the apparent volume of distribution was 5.3 +/- 1.71/kg and the total clearance was 1.28 +/- 0.48 l/kg/h. After the oral dose the elimination had a half-life of 3.2 +/- 1.3 h. The absolute bioavailability of diltiazem ranged from 24 to 74% (mean 42 +/- 18%). The interindividual variation may be explained by a variable first pass effect.