Multiple-dose pharmacokinetics of imipramine and its major active and conjugated metabolites in depressed patients

Imipramine (IMI) and its active metabolites, desipramine (DMI), 2-hydroxyimipramine (2-OH-IMI), and 2-hydroxydesipramine (2-OH-DMI), were assayed by high pressure liquid chromatography in the serum and urine of 14 depressed patients after 1 week of twice-daily treatment with 100 mg of IMI. The concentrations of the glucuronide conjugates of 2-hydroxyimipramine (GA-O-IMI) and 2-hydroxydesipramine (GA-O-DMI) were assessed via enzyme hydrolysis. The range of serum concentrations of IMI and DMI was 65 to 1,064 ng/ml with slight elevation in total active components caused by inclusion of the unconjugated hydroxy metabolites. The average of total active compounds in smokers (239 ng/ml) was less (p < 0.1)than in nonsmokers (524 ng/ml). The mean serum concentration ratios were 0.24 for 2-OH-IMI/IMI and 0.50 for 2-OH-DMI/DMI ratios, whereas the DMI/IMI ratio was 1.88, indicating more extensive accumulation of DMI. Appreciable glucuronide conjugate accumulation occurred with average serum concentration ratios of 8.13 for GA-0-IMI/2-0H-IMI and 6.22 for GA-O-DMI/2-0H-DMI. Covariance occurred in metabolite/precursor ratios indicating intrapatient similarities in formation/disposition rates of the hydroxy pairs and the conjugate metabolite pairs. Renal clearances of 2-OH-DMI were 35 to 267 ml/min, whereas those of the conjugates were only 10 to 110 ml/min. Total urinary recovery of these metabolites was similar to that reported previously for single IMI doses. The data indicate accumulation of substantial serum concentrations of glucuronide conjugates after therapeutic doses of IMI in depressed patients and similarities within patients in disposition of metabolite pairs.