Appropriateness of therapeutic drug monitoring for antidepressants in routine psychiatric inpatient care.

Although there is sufficient evidence of the benefits of therapeutic drug monitoring (TDM) for optimizing antidepressant therapy, its current use in routine care is far from optimal. As a prerequisite for developing improvement strategies, the appropriateness of TDM use was investigated in a psychiatric hospital in which TDM is applied routinely to a large extent. A retrospective analysis of all patients admitted in 2003 with a unipolar depressive disorder was performed. Based on detailed chart review, for all TDM tests, the time of blood sample taking in relation to the medication process and the consequences of the TDM results for clinical decision making were analyzed. Altogether, 748 plasma levels were measured for antidepressants. The evaluation identified considerable inappropriate use of TDM. After a preceding change of dose, only the minority of TDM tests was performed within an optimum time interval. Overall, 30% of blood samples were taken too early, before steady state had been reached. The high number of repeat tests without preceding change of drug dose points to potentially redundant use. There also was evidence of underuse of TDM, as in many cases additional plasma level determinations might have been useful to speed up optimal dosing. Frequent discrepancies were found between the laboratory's recommendations and actual clinical decision making. Suggested dose changes were followed in only 30%. The findings clearly indicate the need for measures to improve the implementation of TDM in routine care. Based on the identified pattern of current TDM utilization and experiences from other fields of medicine, a combination of strategies, including both educational and electronic interventions, may have the greatest potential for improvement.