Impact of single versus multiple dose lithium on renal dysfunction in bipolar patients: A retrospective cohort study

Bipolar disorder significantly affects social functioning and maintenance treatment is crucial. Lithium is considered as a first‐line maintenance treatment in all treatment guidelines, but careful administration is necessary due to concerns about renal dysfunction caused by its use. Lithium can be administered in divided doses from two to three times a day or once a day. However, it is controversial which regimen, single or multiple dose, should be recommended in light of adverse effects. This study aims to clarify the difference in renal dysfunction due to the number of divided lithium doses using data from the electronic medical record in a retrospective cohort.We targeted 72 patients who were prescribed lithium carbonate for bipolar disorder in the Juntendo University Hospital electronic medical record from April 2021 to March 2023. There were 35 cases in the single‐dose group and 37 cases in the multiple‐dose group. The outcome was the change in creatinine and estimated glomerular filtration rate (eGFR) during the observation period. The effect of the regimen was evaluated using multiple regression analysis.There were no significant differences in the change in creatinine and eGFR between the single‐ and the multiple‐dose group, though renal function measured by creatinine and eGFR significantly worsened depending on the duration of treatment or aging.There was no significant difference in renal dysfunction between the single‐dose group and the multiple‐dose group; thus, considering the expected positive effect on adherence, a once‐daily regimen is recommended in maintenance lithium treatment.