An observational study of 110 elderly lithium-treated patients followed up for 6 years with particular reference to renal function.

Background: Recent observational studies have focused on lithium treatment in the elderly, with particular reference to safety in terms of thyroid and renal functions. The purpose of this study was to compare the clinical characteristics of patients starting lithium treatment before (N = 79) or after (N = 31) the age of 65 years. Patients were followed up for 6 years with focus on renal function and prescription of levothyroxine and methimazole.
Results: At baseline, median lithium serum concentration was 0.55 mmol/l. The estimated glomerular filtration rate was lower than 60 ml/min/1.73 m ² in 43 (39%) patients. In a multiple regression analysis controlling for age and gender, we found a significant effect of duration of lithium treatment on estimated glomerular filtration rate (-0.85 ml/min/1.73 m ² per year of prior exposure). The annual decline during follow-up was 2.3 ml/min/1.73 m ² . Two patients were prescribed levothyroxine, and two were prescribed methimazole for the first time during follow-up.
Conclusions: Median lithium serum concentration in this cohort of elderly patients with mainly bipolar disorders was lower than the therapeutic range indicated for younger adults. The decline in glomerular filtration rate may be accelerated by long-term lithium use. Thyroid and renal functions continue to require close monitoring throughout the course of lithium treatment. Trial registration NP/2013/3836. Registered 24 June 2013.