Sex-related differences in the plasma protein binding of lignocaine and diazepam

1 The percentage of lignocaine free in the plasma of ten females receiving oral contraceptive medication was significantly greater than in 17 males of similar age (18--42 years). 2 In the same subjects the percentage of diazepam free in plasma was significantly greater in the contraceptive treated group than in 11 contraceptive-free females and significantly greater in contraceptive-free females than in males. 3 The differences in lignocaine binding were almost completely attributable to changes in alpha 1-acid glycoprotein concentration, which is reduced by oestrogens. The binding of diazepam was significantly related to albumin, alpha 1-acid glycoprotein and non-esterified fatty acid concentrations which together were related to 55% of the variation in the binding of this basic compound.