Metabolic interaction between amitriptyline and perphenazine in psychiatric patients.

1. Steady-state plasma level samples of sixty-five schizophrenic patients from two psychiatric hospitals assigned to three treatment groups (amitriptyline 150 mg/day, perphenazine 20 mg/day and a combination of amitriptyline and perphenazine at 150 mg and 20 mg/day) were assayed for amitriptyline (AT), endogenous nortriptyline (NT) and perphenazine (PPZ) using gas-liquid chromatography. 2. Results reveal that AT and NT levels are independent of sex and hospital environment. 3. PPZ significantly increased the steady-state NT plasma levels, probably through inhibition of the hydroxylation biotransformation pathway, but had no effect on AT levels, thus indicating that PPZ has no influence on the desmethylation pathway, or alternatively, the hydroxylation of AT.