Monitoring amitriptyline and nortriptyline serum concentrations during therapy
Evaluating potential amitriptyline and nortriptyline toxicity
The test may also be useful to evaluate patient compliance
1. Collect specimen immediately before next scheduled dose (minimum 12 hours after last dose).
2. Centrifuge and aliquot serum into plastic vial. Serum must be separated from cells within 2 hours of collection.
This test cannot be performed on whole blood. Serum must be separated from cells within 2 hours of collection; if serum is not removed within this time, tricyclic antidepressant levels may be falsely elevated due to drug release from red blood cells.
Specimens that are obtained from gel tubes are not acceptable because the drug can absorb on the gel and lead to falsely decreased concentrations.
AMITRIPTYLINE AND NORTRIPTYLINE
Total therapeutic concentration: 80-200 ng/mL
Therapeutic concentration: 70-170 ng/mL
Note: Therapeutic ranges are for specimens drawn at trough (ie, immediately before next scheduled dose). Levels may be elevated in non-trough specimens.
Most individuals display optimal response to amitriptyline when combined serum levels of amitriptyline and nortriptyline are between 80 and 200 ng/mL. Risk of toxicity is increased with combined levels are above 500 ng/mL.
Most individuals display optimal response to nortriptyline with serum levels between 70 and 170 ng/mL. Risk of toxicity is increased with nortriptyline levels above 500 ng/mL.
Some individuals may respond well outside of these ranges or may display toxicity within the therapeutic range, thus, interpretation should include clinical evaluation.
Therapeutic ranges are based on specimens collected at trough (ie, immediately before the next dose).