Aspects of amitriptyline and nortriptyline plasma levels monitoring in depression.

Fifty-nine depressed female inpatients were treated with 100 mg amitriptiline (AMT) IM for 4 weeks. Depression ratings and determinations of the parent drug and nortriptyline (NT) were performed weekly. No direct relationship between plasma AMT + NT concentrations and therapeutic response was apparent, but beneficial therapeutic responses and significantly lower side-effect scores were more frequently noted in subjects with concentrations in the 100–200 ng/ml range. AMT + NT concentrations were significantly correlated with age. No significant difference was found in the number of responders between younger and older subjects with two clinical improvement criteria; however, a significant difference emerged when a third more restrictive clinical outcome criterion was adopted. The implications of the present findings for patient treatment and for the interpretation of previous studies are discussed. The data collected point to a possible usefulness of monitoring AMT and NT plasma levels, even if further investigations are needed.