BACKTRACKING SERUM LITHIUM .3. PRELIMINARY-OBSERVATIONS OF PHARMACOKINETIC PARAMETERS IN NORMALS AND PATIENTS

It has been proposed that it might be useful to use a standardised 12 hour serum lithium concentration in the monitoring and management of p atients receiving lithium for recurrent affective disorders. Presently lithium determinations, although assumed to be at approximately 12 ho urs after the dose, are reported without reference to the timing. If t he data were consistent it may be possible to make standard calculatio ns to 'backtrack' lithium to the standard 12 hour serum lithium value from any known time greater than ten hours after a dose. We have carri ed out preliminary data analysis to see whether there is consistency i n sets of data from which may be calculated the rate of decline of ser um lithium at known times after a single dose. We present data which h as been derived from two sources : clinical trials previously publishe d many years ago and a recent, more carefully controlled trial. We bel ieve that there is evidence to suggest that detailed trials are justif ied and that the 'backtracking' technique has promise provided the com ponents of individual variation between and within subjects can be ide ntified.