Lithium elimination half-life and duration of therapy

The elimination half-life (t1/2E) of lithium carbonate in red blood cells, plasma, and urine was measured in 30 patients hospitalized for primary affective disorder. Duration of Li treatment at time of sampling was found to have a direct effect on lengthening time course. Patients on their initial course of Li had the lowest t1/2s: 1.12 (urine), 1.28 (plasma), and 1.22 days (red blood cells); those less than 1 yr on Li had intermediate values: 1.85, and 1.65, and 1.75 days; and those more than 1 continuous year on Li had the longest mean t1/2s: 2.40, 2.43, and 2.24 days. These results for urine (p less than 0.01) and plasma (p less than 0.05) are further evidence that Li may stimulate the production of an endogenous regulator of Li efflux. This regulator may prove to be an important factor in planning of long-term Li prophylaxis.