Prediction of lithium carbonate dosage in psychiatric inpatients using the repeated one-point method.

A repeated one-point pharmacokinetic model of predicting lithium carbonate doses was evaluated. Six psychiatric inpatients with normal renal function who required lithium therapy were given two 600-mg lithium carbonate test doses 12 hours apart. Serum lithium concentrations were determined 11 hours after each test dose. Based on these determinations, the patients were then given individualized lithium doses to reach a minimum steady-state serum concentration of 1.0 meq/liter. The measured and predicted minimum steady-state concentrations were compared. The mean +/- S.D. measured and predicted minimum steady-state serum concentrations for all patients were 1.03 +/- 0.06 meq/liter and 0.97 +/- 0.08 meq/liter, respectively. While further studies are needed to evaluate the method, the repeated one-point pharmacokinetic model provided accurate predictions of lithium carbonate doses in these patients.