Estimation of pharmacokinetic parameters of lithium from saliva and urine

Abstract

The salivary and urinary excretion of lithium was studied in three healthy male sub;ects after oral administration of two or three different doses. In all individuals the concentration of lithium in salivary fluid was found to be 2.2 to 3.3 times as high as the concentration in plasma. In each sub;ect the saliva:plasma concentration ratio remained constant over more than a 100 fold concentration range for at least 3 months. This ratio was not markedly affected by about tenfold changes in saliva flow rate. Thus, pharmacokinetic parameters obtained from salivary excretion data are in agreement with those obtained from plasma concentration and urinary excretion rate data, and renal clearance of lithium can be estimated from salivary excretion data. Diurnal rhythms in the urinary excretion rate of lithium were observed. Thus, once the saliva:plasma concentration ratio is established (by taking only a few blood samples), the measurement of saliva concentrations should prOVide all pharmacokinetic information necessary for rational dosage regimens.