Influence of heparin on the assay of amitriptyline, clomipramine, and their metabolites.

In this study the effect of the use of lithium heparin containers on the plasma levels of amitriptyline, clomipramine, and their metabolites was investigated. Twenty-five patients (10 men and 15 women, mean age 51.8 +/- 14.9 years) taking either amitriptyline or clomipramine in a daily dosage varying from 50 to 250 mg entered the study after giving informed consent. From each patient, blood samples were taken in a sodium edetate container and in a lithium heparin container in random order. Parent compound levels are equal in sodium edetate and lithium heparin containers. Metabolite levels are 5.6% lower in lithium heparin containers. This difference is not considered clinically relevant.