Therapeutic Drug Monitoring (TDM) of Antidepressants for the Treatment of Chronic Musculoskeletal Pain With and Without Depression.

BACKGROUND Antidepressants are recommended for the treatment of chronic musculoskeletal pain; however, target serum concentrations based on therapeutic drug monitoring (TDM) have not been established. Therefore, the authors analyzed routine-care TDM data of antidepressants in patients with chronic pain with and without depression in terms of treatment outcomes in an interdisciplinary multimodal pain treatment (IMPT) program. METHODS Patients with chronic musculoskeletal pain and TDM for amitriptyline (n=45) or duloxetine (n=30) were retrospectively included. The German pain questionnaire for pain intensity and the Depression, Anxiety, and Stress scale were applied at T0 and at the end of the IMPT program (T1). A relief of pain intensity score ≥2 was considered as positive outcome. Comorbid depression was diagnosed based on ICD-10 criteria. Serum concentrations of antidepressants were measured for routine clinical care TDM. RESULTS After IMPT, stress improved in all subgroups, and depressive symptoms improved only in the duloxetine group. Overall, 40% and 27% of patients in the amitriptyline and duloxetine subgroup, respectively, were responders in terms of maximum pain score relief. Responders with comorbid depression were treated with a dose that led to a 1.7-fold higher serum concentration of the active moiety of amitriptyline (amitriptyline+nortriptyline) compared to non-responders. Similarly, a 2.3-fold higher serum concentration was observed in depressed responders than in non-depressed responders (at minimum 131.5 ng/mL). CONCLUSIONS Dosing of antidepressants for chronic pain relief should specifically take comorbid depression into account. TDM may provide better outcomes of pain relief in an IMPT setting in patients with comorbid depression.