Lithium and tricyclic antidepressants.

Pharmacokinetic studies of lithium and tricyclic antidepressants (TCAs) in children and adolescents report similarities to adults with respect to a wide interindividual genetic variation in the rate of elimination and with regard to the linear nature of the system. Children may eliminate these medications more rapidly; therefore, more frequent dosing may be necessary to maintain steady state serum lithium or plasma TCA levels. Doses of these medications necessary for desired blood levels can be obtained from tables based on nomograms (i.e., one-step dosage adjustment determined from a single serum lithium or plasma TCA level drawn 24 hours after administration of a single dose). Use of these dose prediction tables avoids toxicity due to excessively high blood levels in genetically slow metabolizers in whom medication regimes that use mg/kg dose schedules may produce toxic blood levels.