Pharmacokinetics of amoxapine and its active metabolites

The plasma concentrations of amoxapine and its active metabolites, 8-hydroxyamoxapine and 7-hydroxyamoxapine were determined in 8 healthy volunteers receiving a single oral dose of 100 mg of the drug. Considerable interindividual variation was seen in the plasma levels of the three substances. Amoxapine reached maximum levels of 67.4 +/- 35.8 ng/ml between 1 and 2 h after administration. The decline of amoxapine levels in plasma was biphasic. The mean elimination half-life was 9.8 +/- 2.6 h and the estimated first-pass loss ranged between 0.18 and 0.54. The peak levels of the metabolites were reached between 1 and 3 h after administration, with 8-hydroxyamoxapine levels significantly higher than those of 7-hydroxyamoxapine. The mean elimination half-lives were 30.8 and 5.1 h for 8-hydroxyamoxapine and 7-hydroxyamoxapine respectively. The margins of the plasma concentrations reached at steady-state were calculated according to pharmacokinetics parameters for a dosage interval of 8 h.