Bioavailability of metronidazole in rabbits after administration of a rectal suppository

The bioavailability of metronidazole in rabbits was studied using plasma concentration measurements after the administration of the drug in a hydrophilic (glycerogelatin) suppository form. The peak in the plasma concentration time curve occurred about 1 hour after administration, indicating that the rate of absorption is fast and equivalent to that observed in humans after oral administration. There was rapid elimination of the drug, as indicated by a relatively high elimination rate constant and low plasma half-life. The in vitro dissolution profile of the suppositories further confirms rapid absorption of the drug from the suppositories in the rectum. The presence of Tween 80 enhanced the in vitro release of metronidazole, but the presence of a hydrogenated vegetable oil lubricant (Lubritab) caused retardation in the drug release from the suppositories.