Predicting lithium dose by the body-weight method.

A method for predicting steady-state lithium concentration based on body weight calculated at 0.5 mEq/kg/day produced serum levels within the therapeutic range of 0.6 to 1.2 mEq/l in 20 of 23 patients (22 patients if the less conservative level of 1.4 mEq/l had been used). Had the one-point method been used, in which doses are based on the serum lithium concentration 24 h after a 600 mg test dose, the doses would have been lower in 20 of 23 patients. This neglected approach to predicting lithium doses could scarcely be either more accurate or simpler.