Interindividual differences in plasma protein binding of nortriptyline in man ? A twin study

Abstract

The binding ratio,rA, of plasma proteins for nortriptyline (NT), a tricyclic antidepressant drug, was investigated by a plasma-plasma equilibrium dialysis technique at 4°C in 7 identical and 10 fraternal sets of twins. The mean steady-state plasma concentrations of NT during oral administration of NT (0.2 mg per kg body weight, t.i.d. for 8 days) were known for all subjects from a previous study. — A two-fold variation inrA was found (from 0.86 to 1.55), and there were significant intrapair differences inrA, both in identical (P<0.01) and fraternal pairs (P<0.0005). The variance ofrA between individuals within pairs was significantly greater in dizygotic than in monozygotic twinships (P<0.025). — It is concluded that plasma protein binding of NT is influenced both by environmental and genetic factors. The interindividual differences in NT-binding to plasma proteins could not be correlated with variations in its steady-state plasma concentrations.