Lithium pharmacokinetics, duration of therapy, and the adenylate cyclase system

The elimination half-life of lithium carbonate in red blood cells, plasma, and urine was measured in 30 patients hospitalized for primary affective disorders. The duration of lithium treatment at the time of sampling was found to have a direct effect on lengthening time-course. Those on their initial course of lithium had the lowest half-lives (in days): 1.12 (urine), 1.28 (plasma), and 1.22 (red blood cells); those with less than 1 year of lithium had intermediate values: 1.85, 1.65, and 1.75, and those with more than 1 year of continuous lithium administration had the highest mean half-lives: 2.40, 2.43, and 2.24. The significance of these results for urine (p less than 0.01) and plasma (p less than 0.05) indicates further evidence that lithium may stimulate the production of an endogenous regulator of lithium efflux. 8 of these patients had lumbar punctures before lithium administration: those with previous treatment with lithium had higher mean cyclic adenosine monophosphate levels than those taking it for the first time. These results are discussed in the context of the possible mechanisms of lithium action.