Bioequivalence and pharmacokinetic profile of promethazine hydrochloride suppositories in humans.

A bioequivalence study of promethazine hydrochloride (10-[2-(dimethylamino)propyl]-phenothiazine monohydrochloride) was conducted in 20 male human subjects with the purpose of comparing, under blind condition, the human serum levels of promethazine in three different formulations. The formulations tested were a 50-mg promethazine hydrochloride polyethylene glycol suppository, a 50-mg promethazine hydrochloride cocoa butter-white wax suppository, and a 50-mg oral dose of promethazine hydrochloride syrup. Each subject received single doses of each of the three formulations on each of three different days on a crossover basis. From the measured serum levels, estimates of the bioavailability parameters (area under the serum concentration versus time curve, time-to-peak serum concentration, and peak serum concentration) were obtained by least-squares digital computer fitting. Also, a one-compartment pharmacokinetic open model with two consecutive first-order input steps is proposed. Statistical analysis of the results was performed by using a linear multiple regression approach for the analysis of variance. No significant differences between the syrup and the polyethylene glycol suppositories were obtained (p greater than 0.05) for the above three bioavailability parameters. However, the polyethylene glycol suppositories provided statistically higher peak serum concentration, shorter time-to-peak serum concentration, and larger area under the serum concentration versus time curve than the cocoa butter-white wax suppositories.