Rectal absorption of omeprazole from suppositories in rabbits

Rectal absorption of omeprazole, a proton pump inhibitor, from suppositories was studied in rabbits. The suppositories were prepared by the conventional melting method with two types of bases, water-soluble polyethylene glycol (PEG) 4000 and oil-soluble Witepsol H15 bases, and administered intrarectally (ir) to rabbits at a dose of 10 mg omeprazole/kg. The plasma omeprazole concentration-time profiles of the two suppositories were compared with those following intravenous (iv) administration of the same dose. There were no significant differences between the two suppositories in bioavailabilities and peak plasma concentrations (Cmax). Bioavailabilities and Cmax of PEG- and Witepsol suppositories were 30.3 and 33.9%, and 7.0 and 5.6 μg/ml, respectively. However, PEG suppository showed significantly (P