Protein Binding of Indomethacin: Binding of Indomethacin to Human Plasma Albumin and its Displacement from Binding by Ibuprofen, Phenylbutazone and Salicylate, <i>in vitro</i>

Abstract

The reversible binding of indomethacin to human plasmaprotein and the manner in which this may be modified by ibuprofen, phenylbutazone and salicylate was studied by ultrafiltration at 37 °C and pH 7.4. Indomethacin is much more highly bound than has previously been considered. The affinity constant for the single primary binding site is 3 x 105 l/mol and for the seven secondary binding sites 1.4 x 104 l/mol. The protein binding of indomethacin is increased by the presence of phenylbutazone and decreased by the presence of ibuprofen and salicylate. Salicylate in vitro, at concentrations observed clinically, significantly decreases the protein binding of indomethacin.