Binding of indomethacin ester with tropic acid to human serum albumin.

The binding affinities of the ester of indomethacin with tropic acid and of indomethacin to human serum albumin were studied using the method of equilibrium dialysis. The binding constants were calculated from the experimental data by the Scatchard model. Binding to human serum albumin (14 X 10(-5) mol/l) was significantly lower for esterified indomethacin than for nonesterified. The tropic ester of indomethacin has an association constant for the primary binding sites of 2.16 X 10(5) l/mol, and while the association constant for indomethacin is 8.15 X 10(5) l/mol. The differences found between the binding affinities of the ester of indomethacin and of indomethacin may contribute to the different pharmacokinetics of these drugs.