BIOAVAILABILITY AFTER RECTAL ADMINISTRATION OF THIAZINAMIUM METHYLSULFATE IN DIFFERENT VEHICULES

The bioavailability in humans of the quaternary ammonium compound thiazinamium methylsulphate (Multergan) was studied using plasma concentration measurements after the application of the drug in a lipophilic (Witepsol H-15) and a hydrophilic (a polyethylene glycol mixture) suppository base. The best results were obtained with Witepsol H-15. The peak in the plasma concentration-time curve appeared about 60 min after administration, indicating that the rate of absorption is faster than that observed after oral administration. After the maximum, the curve declined rather rapidly, and usually dropped to zero or almost zero concentration in7h. The bioavailability obtained with Witepsol H-15 suppositories was about 6% of the dose, which is of the same order of magnitude as after oral administration. Interindividual variation was also similar to that obtained after oral administration. After the application of the drug in the polyethylene glycol base, very low plasma concentrations were found and the bioavailability was almost negligible. © 1979.