Promotion of Rectal Absorption of Sodium Ampicillin by Disodium Glycyrrhetinic Acid 3β-O-Monohemiphthalate in Rats

The promotional effect on rectal absorption of sodium ampicillin (ABPC) by the glycyrrhetinic acid derivative disodium glycyrrhetinic acid 3β-O-monohemiphthalate (GA MHPh) was studied in rats and compared with those of sodium caprate (CAP) and sodium glycocholate (GLY). Duration of the promotive effect of GA MHPh was also studied. Rectal absorption of ABPC was significantly enhanced by addition of GA MHPh at an optimum concentration of about 1.5%. The plasma maximum concentration of ABPC was 78.71 μg/ml 10 min after its rectal administration at 100 mg/kg with 1.5% GA MHPh. The bioavailability of ABPC with and without 1.5% GA MHPh was 82.12% and 3.92%, respectively. Thus, absorption of ABPC in the presence of 1.5% GA MHPh was about 21 times that of ABPC alone. GA MHPh was more effective as an absorption promoter than either CAP or GLY. Its promoting action on the mucosal membrane was apparent immediately, reached a maximum at 5 min and remained for at least 20 min after rectal administration of the solution. It is therefore suggested that GA MHPh is a very useful promoter absorption of the hydrophilic drug ABPC when administered rectally.