Are there any known interactions between methotrexate and amitriptyline?/nBackground: A patient wit

Fråga: Are there any known interactions between methotrexate and amitriptyline?

Background: A patient with methotrexate-treated psoriasis also suffers from neurogenic pain after a cardiac catheterisation. The pain was previously treated with a tricyclic antidepressant which has been withdrawn for unknown reasons. The questioner wants to know if there is a contraindication for reinstitution of amitriptyline treatment.

Sammanfattning: No documentation on possible interaction between methotrexate and amitriptyline was found. The possibility of such an interaction is remote and can be checked using therapeutic drug monitoring.

Svar: A thorough literature search gave no documentation concerning an interaction between methotrexate and amitriptyline or any other tricyclic antidepressant. Methotrexate is excreted unchanged in the urine (1) while amitriptyline is metabolised via CYP2D6 and other cytochrome P-450 enzymes (2). A pharmacokinetic interaction is therefore not likely. Because both drugs can be measured in plasma a pharmacokinetic interaction can easily be detected. 1 FASS 1999 (The Swedish catalogue of approved medical products) p. 819-820 2 FASS 1999 (The Swedish catalogue of approved medical products) p. 1386