Determinants of d-tubocurarine plasma protein binding in health and disease

d-Tubocurarine protein binding was determined in plasma from normal surgical patients; patients with renal dysfunction; patients with alcoholic cirrhosis; and patients scheduled for coronary artery surgery and was compared with binding determined in solutions of isolated human serum albumin (HSA). The free fraction of d-tubocurarine was independent of plasma drug concentration throughout the range 0.1-3.0 micrograms/ml. The free fraction of d-tubocurarine in renal disease (0.44 +/- 0.05), liver disease (0.53 +/- 0.05), and cardiac disease (0.49 +/- 0.05) was not significantly different from that in normal patients (0.50 +/- 0.04). Furthermore, the free fraction of d-tubocurarine was unrelated to plasma concentrations of total protein, total globulin, albumin, total lipids, or alpha 1-acid glycoprotein in the four patient groups. The free fraction of d-tubocurarine (0.55 +/- 0.02, n = 7) in solutions of HSA (0.58 mM) was similar to that observed in plasma. Albumin, therefore, appears to be the major plasma binding protein for d-tubocurarine.