Variable binding of propranolol in human serum

Abstract

Human serum proteins were fractionated by ultracentrifugation and gel filtration. Binding of propranolol was determined by equilibrium dialysis. Propranolol was distributed to lipoproteins independent of drug concentration. Two groups of propranolol binding sites were found to be present in the protein preparation containing albumin, α 1-acid glycoprotein, transferrin and prealbumin. The first binding site with a dissociation constant of 7.5 × 10 −7 was present in number equivalent to concentration of α 1-acid glycoprotein. The propranolol binding to serum samples from 21 healthy males expressed as binding ratio B/F and per cent binding ranged from 7.5 to 19.2 and 88.2 to 95.0 respectively. The binding ratio was correlated to concentration of α 1-acid glycoprotein ( r = 0.85, P < 0.001), but not to concentrations of albumin and lipoproteins. The results indicate that α 1-acid glycoprotein is the main propranolol binding protein in human serum.