Imipramine and amitriptyline plasma concentrations and clinical response in major depression

Plasma drug concentrations and clinical response were measured in two groups of hospitalised depressed patients, who received amitriptyline or imipramine double-blind in a dosage of 250 mg for four weeks. Virtually no significant linear or curvilinear relationships were found between any plasma measure and any measure of clinical response. Modest but significant direct relationships were found between age and concentration of parent drugs but not demethylated metabolites. Blood drug level measurement therefore appears to be of little value in monitoring drug treatment of depressed in-patients.