Therapeutic Drug Monitoring Characteristics in a Tertiary University Hospital in 2019

Introduction Therapeutic drug monitoring (TDM) is defined as measuring drug concentration in a biological sample to optimize pharmacotherapy. This study aims to evaluate TDM requests in a tertiary university hospital retrospectively. Materials and methods TDM requests were evaluated retrospectively for lithium, valproic acid, carbamazepine, and digoxin in 2019. The age and gender of the patient, requesting department, and measurement results were evaluated. Lower levels than the reference values were considered as subtherapeutic, while levels higher than the reference were considered as toxic. Results A total of 415 drug level measurement records were found. The pediatric age sample ratio was 13.7%, and the elderly age sample ratio was 11.8%. When all samples were evaluated according to the relevant laboratory cut-off values, 72.8% of samples were within the therapeutic level range, 21.9% of samples were subtherapeutic, and 5.3% were toxic. The pediatric age group had a higher ratio of toxic levels for the four drugs studied (54.5%). Conclusions Tests for lithium, valproic acid, carbamazepine, and digoxin would not be considered sufficient for TDM. Multidisciplinary teamwork might be appropriate for further implementation and interpretation of TDM.