Appropriateness of Therapeutic Drug Monitoring for Lithium
Chaveewan Ratanajamit BPharm, PhD*, Suchada Soorapan BPharm, PhD*, Thitima Doang-ngern BPharm MSc*, Wudtikai Waenwaisart BPharm**, Laksamee Suwanchavalit BPharm*, Siwaporn Suwansiri BPharm*, Sopit Jantasaro BPharm*, Itsaree Yanate BPharm*
Affiliation : * Department of Clinical Pharmacy, Faculty of Pharmaceutical Sciences, Prince of Songkla University, Hat Yai, Songkhla ** Head of Pharmacy Department, Songkhla Psychiatric Hospital, Songkhla
Objective : Evaluate the appropriateness of therapeutic drug monitoring (TDM) for lithium.
Materials and Methods : 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 some-
what 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
