Plasma and brain pharmacokinetics of amitriptyline and its demethylated and hydroxylated metabolites after acute intraperitoneal injection in mice.

The fate of amitriptyline (AMI) and its demethylated and hydroxylated metabolites was studied in Swiss CD1 mice, after acute intraperitoneal injection of AMI (20 mg/kg). Levels of each compound were determined to establish pharmacokinetic parameters in plasma and brain. Absorption and elimination of AMI were rapid (tmax = 0.37 h and 0.42 h, and t1/2 = 3.2 h and 3.6 h in plasma and brain, respectively). In plasma, 10-OH-nortriptyline was the main metabolite (46% of AUC) and 10-OH-amitriptyline reached significant levels but only during the first hour. In brain, AMI (43% of total AUC), nortriptyline (NOR) (29%) and demethylnortriptyline (DM-NOR) (11%) were the most abundant compounds, possibly through high blood-brain barrier transfer and/or marked intracerebral demethylation. Brain OH-metabolite levels were much lower. Knowledge of kinetic parameters and metabolism of AMI can help in the evaluation of pharmacological activity.