Gentamicin binding to serum and plasma proteins.

Gentamicin binding to serum proteins was studied by equilibrium dialysis at 37 degrees C and pH 7.4 in the presence of both physiologic and adjusted concentrations of ionized calcium and magnesium. The percentage of bound drug was inversely related to the concentration of these two divalent cations, raning from 27% bound with no calcium and magnesium present to 17% bound in the presence of four times physiologic concentrations. No significant difference in the extent of drug-protein binding was noted in a comparison of sera from healthy and uremic subjects. Heparin also was found to affect gentamicin binding. Increasing heparin concentration in serum increased apparent gentamicin-protein binding to 34% in the presence of physiologic amounts of calcium and magnesium. Buffered heparin solutions without plasma proteins bound up to 65% of total drug concentration. Gentamicin-protein binding may have implications regarding pharmacokinetics and renal cortical uptake.