Rectal absorption enhancement of gentamicin in rabbits from hollow type suppositories by sodium salicylate or sodium caprylate.

The absorption of gentamicin (GM) from the rectum of rabbits after coadministration of GM (60 mg) and sodium salicylate (SA) or sodium caprylate (CA) as absorption-enhancing agents was investigated. Two types of hollow type suppositories were used--a conventional type (Type I) and a release-restricted type (Type II). Without SA or CA, GM was not absorbed. However, GM absorption was marked when 90 mg of solid SA or CA was added (the bioavailability of GM was 58% with SA, and 59% with CA). The enhancing effect of SA or CA (30 mg) in solid or aqueous solution form on GM absorption was evaluated using the Type I suppository. In the case of SA, the highest plasma GM level (Cmax 15.3 +/- 1.7 micrograms/ml, AUC0-4 27.3 +/- 3.9 h.micrograms/ml) was obtained following coadministration of powdered GM and SA; the plasma GM level (Cmax 1.5 +/- 0.6 micrograms/ml, AUC0-4 3.0 +/- 1.3 h.micrograms/ml) following the administration of a solution of GM and SA was significantly decreased as compared with the results using the powdered form. In the case of CA, the plasma GM level (Cmax 14.8 +/- 4.5 micrograms/ml, AUC0-4 25.4 +/- 8.7 h.micrograms/ml) following administration of the solution form was not significantly decreased in comparison with the results obtained using the powdered form. A marked increase in the enhancing effect of SA on the rectal GM absorption was found following use of Type II suppositories when GM and SA were coadministered in solution form. However, the GM absorption after coadministration of GM and CA using Type II suppositories was not significantly different from the absorption resulting from use of Type I suppositories. Our results suggest that the form and concentration of drug should not be ignored in evaluating the enhancing effects of SA or CA on the rectal absorption of poorly absorbed drugs such as GM.