Pharmacokinetics of desmethylimipramine and nortriptyline in man after single and multiple oral doses ? A cross-over study

Abstract

Eight healthy volunteers received single oral doses (1 mg/kg) and 6 received multiple doses (0.4 mg/kg t.i.d. for 2 weeks) of desmethylimipramine (DMI) and nortriptyline (NT) on different occasions. Kinetic analysis of plasma levels of the drugs showed that the ratios between single-dose peak-levels, plasma half-lives and apparent mean “steady-state” plasma levels of the two drugs were constant in all the subjects, and averaged 0.6. Despite their closely related chemical structures the apparent plasma clearance rate of DMI was about twice that of NT, and this might be associated with their different degrees of binding to plasma proteins. — The “steady-state” plasma level of NT in man is known to be genetically determined, and the conformity within each individual of the plasma clearance rates of DMI and NT indicates that the plasma kinetics of both these drugs are controlled by common genetic factors. — The study also shows that the “steady-state” plasma level of DMI, like that of NT, can be predicted accurately from single-dose plasma-level data. Thus, if the kinetic characteristics of one of these drugs in a subject are known, it is possible to predict the plasma kinetics of the other compound.