Comparison of standard and low serum levels of lithium for maintenance treatment of bipolar disorder.

In recent years, lower serum levels have been recommended for maintenance therapy with lithium. We studied 94 patients with bipolar disorder in a randomized, double-blind, prospective trial of two different doses of lithium for maintenance therapy: the "standard" dose, adjusted to achieve a serum lithium concentration of 0.8 to 1.0 mmol per liter, and a "low" dose, resulting in a serum concentration of 0.4 to 0.6 mmol per liter. The group medians of the patients' average serum lithium levels were 0.83 mmol per liter for the patients in the standard-range group and 0.54 mmol per liter for those in the low-range group. Six of 47 patients (13 percent) assigned to receive lithium doses that would produce serum levels in the standard range had relapses while on protocol, as compared with 18 of 47 (38 percent) assigned to the low-dose range. The risk of relapse was 2.6 times higher (95 percent confidence interval, 1.3 to 5.2) among patients in the low-range group than among those in the standard-range group. Side effects, including tremor, diarrhea, urinary frequency, weight gain, and a metallic taste in the mouth, were more frequent in the standard-range group. We conclude that doses resulting in serum lithium levels from 0.8 to 1.0 mmol per liter are more effective in treating bipolar disorder than those that result in lower serum lithium concentrations, although the higher doses are associated with a higher incidence of side effects. Recent findings about the limited nephrotoxicity of lithium, along with our observations, suggest that physicians should attempt to maintain serum lithium levels between 0.8 and 1.0 mmol per liter in most patients with bipolar disorder and that they should attempt to enhance patients' understanding of and compliance with this regimen.