Pharmacokinetics of lithium carbonate in children

The pharmacokinetics in both serum and saliva of a single oral dose of lithium carbonate 300 mg was investigated in nine children aged 9 to 12 years. The serum and saliva concentration-time curves were parallel and biexponential, with a fast distribution phase after the peak at the second hour and a slow elimination phase starting from the 12th hour. The fast phase half-life was 6.0 +/- 1.8 hour in the serum, and 5.8 +/- 1.9 hour in the saliva. The slow phase half-life was 17.9 +/- 7.4 hour in the serum and 15.6 +/- 8.2 hour in the saliva. Lithium was 2.84 +/- 0.86 times higher in the saliva than in the serum, with a saliva/serum r coefficient of correlation of 0.93. A relatively large error was found in predicting serum levels from saliva. There were significant intersubject differences in the saliva/serum ratio, which point to the need for individual ratios in clinical use. On the whole, the pharmacokinetics of lithium in children had the same features as in adults, with a trend toward a shorter elimination half-life and higher total clearance.