Renal side effects of lithium: the importance of the serum lithium level.

Patients given long-term treatment with lithium often develop an impairment of renal water reabsorption which may lead to clinically significant adverse reactions. A convenient measure of this impairment may be obtained using the ratio of urine volume (V) divided by lithium clearance (CLi). When data from a large group of patients were recalculated, this ratio showed a statistically significant correlation with the serum lithium level. This finding supports the suggestion that patients might advantageously be maintained at lower serum levels than those commonly employed.