Rectal absorption of omeprazole from suppository in humans

The oral absorption of omeprazole is incomplete, in part due to first-pass metabolism. We investigated the feasibility of rectal administration of omeprazole by comparing its absorption from a Witepsol H15-based rectal suppository and an orally administered commercial gelatin capsule in 10 male volunteers. Profiles of plasma concentration between two preparations (20 mg) were not statistically different, indicating that the rate and the extent of absorption were similar. Paired t-test revealed no significant differences in area under the curve, mean residence time, and time to peak concentration between two preparations. On the other hand, lag time of absorption and peak concentration were statistically different (p < 0.05) between these preparations. Under these experimental conditions, the rectal route did not produce an improvement in the extent of absorption over an oral capsule.