Differences in the binding of drugs to plasma proteins from newborn and adult man. II.

The binding of certain drugs to isolated fractions of plasma proteins obtained from newborn and adult man has been studied by equilibrium dialysis. For thiopental, desipramine, nitrofurantoin, sulfamethoxydiazine, meticillin and salicylic acid no difference was found between binding to the albumin fraction from newborns and adults. However, for thiopental, desipramine and promethazine binding to the globulin fraction was smaller in the newborns than in adults. Addition of bilirubin to the albumin fraction decreased the binding of nitrofurantoin, sulfamethoxydiazine and meticillin. No difference in the binding of meticillin to the albumin or globulin fractions from newborns and adults was found. The binding decreased, however, if both fractions were combined. Four mechanisms to explain the difference in binding between newborns and adults are discussed: (1) Displacement of drugs by bilirubin, (2) different binding properties of cord and adult albumin, (3) different properties of the globulins and (4) interaction of albumin with globulins in the newborn.