Effect of bovine serum albumin on the absorption of sulfonamides in the rat.

Effect of bovine serum albumin (BSA} on the absorption of sulfonamides was studied employing in situ recirculating perfusion method in the rat. The absorption rate constant of sulfamethoxazole was greatly decreased by addition of BSA to the perfusion solution. But, the decreasing effect of BSA on the absorption rate was diminished after removing BSA from perfusion solution. The decreasing effect of BSA on the absorption rate constant of sulfanilamide was not observed. The binding of sulfonamides to BSA was studied using an equilibrium dialysis method. Sulfamethoxazole was bound to large extent, whereas sulfanilamide was little bound. The bound fraction of sulfamethoxazole increased as the concentration of BSA increased. Influence of BSA on permeability of intestinal mucosa was not observed. Thus, the decreasing effcet of BSA on the absorption rate constant of sulfamethoxazole was attributed mainly to the binding to BSA which results in the decrease of unbound drug permeable to mucosal membrane. However, experimental results were slightly deviated from the theoretical value calculated by assuming that bound drug was unabsorbed from the intestinal mucosa. 287