The importance of monitoring renal function and concomitant medication to avoid toxicity in patients taking lithium

Lithium, which is used for bipolar disorder, can cause toxicity. There are two categories of lithium toxicity, namely, overdose-related and not overdose-related. However, the treatment and prognosis of each type of toxicity are not clearly understood. We, therefore, compared the clinical characteristics of patients with overdose-related and not overdose-related lithium toxicity. Relevant data were obtained from the medical records of 16 patients with lithium toxicity, and renal function and concomitant medications were retrospectively compared between the two groups. We also compared the treatment for, manifestations of, and duration of hospitalization between the two types of lithium toxicity. The not overdose-related group more frequently had a low creatinine clearance (<50 mL/min) than did the overdose-related group (P = 0.01). Multivariable regression analysis demonstrated that creatinine clearance <50 mL/min was a significant predictor of lithium toxicity in the not overdose-related group (P = 0.01). Tremor and dysarthria occurred only in the not overdose-related group, and duration of hospitalization was significantly longer in the not overdose-related than overdose-related group (P = 0.01). Clinicians must monitor the renal function of patients taking lithium, even when in compliance with the prescribed dosage, because they are at long-term risk of lithium toxicity.