Therapeutic Drug Monitoring and Adverse Drug Reactions of Lithium in Patients Diagnosed with Bipolar Affective Disorder at a Tertiary Care Center in Eastern Nepal

Lithium is a widely used mood stabilizer in management of bipolar affective disorder but its narrow therapeutic index (0.6–1.2 mmol/L) requires therapeutic drug monitoring to ensure both efficacy and safety. This descriptive cross-sectional study was conducted in the Psychiatry Ward of B.P. Koirala Institute of Health Sciences, Dharan, Nepal, over a period of 9 months (July 2022 to March 2023). Serum lithium concentrations and associated adverse drug reactions following lithium therapy in hospitalized patients with bipolar affective disorder was assessed, while also categorizing serum lithium levels as sub therapeutic, therapeutic, or supra-therapeutic. A total of 46 patients diagnosed with bipolar affective disorder and receiving lithium therapy were enrolled via convenience sampling. The mean age of participants was 29.13±9.25 years, with a male predominance (58.7%). Most patients (63.0%) had serum lithium levels within the therapeutic range (0.6-1.2 mmol/L), while 21.7% were sub-therapeutic (<0.6 mmol/L) and 15.2% were above the therapeutic range (>1.2 mmol/L). The most common adverse drug reaction was hand tremor (33.0%), followed by weight gain (22.7%), difficulty concentrating (16.7%), leukocytosis (7.6%), hypothyroidism (6.1%), nausea (4.5%), polyuria (4.5%) and polydipsia (4.5%). The findings highlights that although most patients achieved therapeutic lithium levels, a significant proportion had levels outside the target range. Routine monitoring of serum lithium levels, along with timely dose adjustments is therefore essential to optimize treatment outcomes and minimize adverse effect.