Nortriptyline capacity-limited metabolism: a case report.

A case report of a 62-year-old patient is presented with apparent dose-dependent kinetics for nortriptyline following the administration of therapeutic doses of the drug. Twelve-hour measurements of total plasma nortriptyline following steady state administration of the drug at 10 mg every other day, 10 mg daily, and 25 mg daily were 38, 86, and 647 ng/ml and while free plasma nortriptyline concentrations were 0.37, 0.9, and 6.6 ng/ml, respectively. Half-lives calculated from samples collected at 12, 24, and 36 hours status after administration of steady state 10 mg every other day, 10 mg daily, and 25 mg daily maintenance doses were 30.4, 36.7, and 64 hours, respectively. Toxicity did not occur despite excessive total plasma tricyclic antidepressant concentrations as a result of abnormally increased plasma protein binding of nortriptyline. The case is contrasted to the usual pharmacokinetic characteristics for the tricyclic antidepressants.