The systemic availability of meptazinol in man after oral and rectal doses.

We have studied the pharmacokinetics of the centrally-acting analgesic meptazinol after oral and rectal administration to 15 healthy men. Each subject took a standard 200 mg tablet orally and Witepsol H12 suppositories containing 75, 100, and 150 mg of the drug in a cross-over design. Meptazinol plasma concentrations were measured by HPLC using fluorescence detection and the pharmacokinetics determined. The tmax values for the 100 mg and 150 mg suppositories (median = 0.5 h) were statistically significantly shorter than for the tablet (median = 1.13 h), suggesting that meptazinol was more rapidly absorbed via the rectal route. Despite substantial intersubject variation in Cmax the plasma concentrations after rectal dosage were higher than after oral administration. There was a statistically significant (p less than 0.001) improvement in systemic availability for each of the suppository doses (mean approximately 15.5% compared with the oral tablet (mean approximately 4.5%).