Maintenance-dose prediction based on a single determination of concentration: general applicability to two-compartment drugs with reference to lithium.

A general approach to the selection of the maintenance dose (Dm) required to give a desired steady-state concentration of drug based on a single determination of concentration after a test dose (C*) is extended to drugs with two-compartment pharmacokinetic characteristics. Using the equation developed, the value of the proportionality factor relating 1/Dm to C was found to be within 3.2% of the value calculated from a published nomogram for lithium. The inherent error is shown to be a function of the value of the hybrid rate constants alpha and beta, as well as the value of an intercompartmental transfer rate constant, k21, in an individual.