Objective: Evaluate the appropriateness of therapeutic drug monitoring (TDM) for lithium.

Material and Method: A retrospective chart review of all patients who received lithium for treatment of psychiatric disorders between January 2004 and October 2005 was done. The present study was investigated in a psychiatric hospital in Thailand. Based on detailed chart review, the appropriateness of TDM utilization comprised of three aspects, i.e., the indication of TDM request, the time of blood sample taking in relation to the medication process, and the clinical applications of the reported serum lithium levels, were evaluated. The Morecambe Bay Shared Care Guideline 2003 was modified and used as criteria for evaluation. Altogether, 91 serum lithium samples were measured among 60 patients.

Result: In 66 (72.5%) of requests, clear indications for lithium TDM were recorded i.e., initiation therapy 41.8%, suspected toxicity 15.4%, patient compliance assessment 5.5%, after regimen changes 5.5%, and therapeutic failure 4.4%. Routine tests without specified indications were found in the remainder (27.5%), all were in-patients, which pointed to potentially redundant use. The time of sample taking was recorded in 37 (40.6%) of blood samples, all were taken from in-patients, after steady state had been reached. These data for out-patients were not recorded, except one noted that blood sample was drawn after the patient had not received lithium for four days. Serum lithium levels were reported in 83 (91.2%) samples. Of these, 37 (44.6%) were out of therapeutic range, and only 12 required dosage alterations. The evaluation demonstrated somewhat inappropriate use of reported lithium levels. Dose changes were done in some patients who required dosage adjustment. Among 14 toxicity-suspected patients, nine actually had serum lithium levels exceeding the therapeutic range. Of these, only one patient was subsequently switched to a reduced dose, three patients were discontinued while five patients were prescribed the pre-TDM doses. Similarly, in five toxicity-suspected patients whose serum lithium levels were below therapeutic range, lithium was discontinued in three patients and no dosage alteration, which was considerably acceptable, in two patients. The doses were increased in three out of four inadequately controlled patients whose serum lithium was lower than the therapeutic range. Overall, in only 33 (36.3%) requests was TDM performed appropriately according to the indication, sampling time and subsequent dose adjustment.

Conclusion: The findings indicate the need to improve the utilization of TDM for lithium. Education for hospital personnel on appropriateness of serum sample collection, interpretation, and proper use of serum drug levels is encouraged. Development of a request form containing essential data, such as indication for TDM, current drug dosing regimen, time of last dose, patient compliance, test results and interpretations and clinical decision made, can help optimize TDM use and reduce unnecessary costs.

Keywords: Therapeutic drug monitoring, TDM, Lithium, Mania, Bipolar disorder