Effect of Tetracyclines on the Absorption of Drugs from the Intestine. I. : Effect of Tetracycline on the Absorption of Sulfanilic Acid

Effect of tetracycline on the absorption of sulfanilic acid was examined in the rat. It was found that, in the presence of tetracycline, sulfanilic acid disappeared faster from the small intestinal recirculating solution at pH 8.0. At pH 6.0, however, this absorption enhancement effect of tetracycline was not observed. Blood level analyses of sulfanilic acid were carrid out in the rat using in situ single loop preparation. In the presence of tetracycline, blood level of sulfanilic acid increased at pH 8.0 but not at 6.0 and this result agreed with the one obtained from intestinal recirculation method. Partition ratio (organic solvents/water) and UV spectral data of sulfanilic acid showed the absence of interaction between sulfanilic acid and tetracycline in recirculating solution. Results from tetracycline pretreatment experiments showed that sulfanilic acid disappeared faster from recirculating solution even in the absence of tetracycline. These results suggested that the increased absorption of sulfanilic acid is not due to complex formation with tetracycline in the gut lumen but to the direct effect of tetracycline on the absorptive membrane.