Pharmacokinetics of the new analgesic, meptazinol, after oral and intravenous administration to volunteers.

The pharmacokinetics of meptazinol (Meptid) have been studied in nine male volunteers after single and multiple oral administration of 200 mg tablets and also after a single 25 mg intravenous dose. Plasma concentrations of meptazinol were determined by HPLC using fluorescence detection. Drug absorption after oral dosage was rapid, peak plasma concentrations being reached between 0.25 and 2 h after drug administration. Subsequent elimination proceeded in an apparently mono-exponential fashion with a half-life of 2 h, although after intravenous dosage there was evidence of an initial rapid distributive phase. The mean total plasma clearance was 2.21/min and the mean apparent volume of distribution (Vd beta) was 4.99 l/min. The bioavailability ranged from 1.9 to 18.5% (mean = 8.7%) and was related to the rate of absorption. Multiple dosing, 6-hourly for 3 days, did not produce any accumulation above that predicted from a single dose. Plasma protein binding of the drug was 27.1% and did not vary over the therapeutic concentration range of 25 to 250 ng/ml.