Backtracking serum lithium .1. Clinical rationale and theoretical aspects

Clinical determinations of serum lithium are conventionally determined twelve hours after the last dose of lithium. In practice this is probably rarely attained since, for various practical reasons, it may be difficult for patients and physicians to meet exactly twelve hours after the dose. The present paper describes the clinical rationale for the twelve hour determination and proposes a means by which this may be pharmacokinetically backtracked from samples taken between twelve and twenty four hours after the last dose. This method may then be applied using the Lithium Ion Selective Electrode analyser to obtain accurate, standardised lithium levels instantaneously and in the presence of the patient.