AN ASSESSMENT OF ERYTHROCYTE LITHIUM CONCENTRATIONS AS A MEASURE OF PATIENT COMPLIANCE

Following oral administration of only one dose of lithium (e.g. just p rior to a clinic brood test), plasma concentrations rise quickly and m ay appear to be in the therapeutic steady state range for several hour s. At the clinic, therefore, noncompliance may go undetected. It has b een suggested that measurements of erythrocyte lithium concentrations (Le) may be more useful than plasma lithium concentrations (Lp) in det ecting patient noncompliance. This was investigated by comparing the p harmacokinetics of lithium in plasma and erythrocytes after a single 8 00 mg dose of lithium carbonate and during constant dosing around stea dy state. Twelve healthy male volunteers took part in the study and to ok 800 mg of lithium carbonate (Priadel) for 28 days. Le and Lp ranges were determined around steady state using data obtained from eight vo lunteers known to be compliant. Compliance was measured using electron ic monitoring. Both erythrocyte and plasma lithium concentrations reac hed values comparable to steady state after a single oral dose. This s uggests that Le measurements are no better than Lp measurements when a ttempting to identify noncompliant patients who only dose shortly befo re a blood test.