| Abstract: | Following oral administration of only one dose of lithium (e.g. just prior to a clinic blood test), plasma concentrations rise quickly and may appear to be in the therapeutic steady state range for several hours. At the clinic, therefore, noncompliance may go undetected. It has been suggested that measurements of erythrocyte lithium concentrations (Le) may be more useful than plasma lithium concentrations (Lp) in detecting patient non-compliance. This was investigated by comparing the pharmacokinetics of lithium in plasma and erythrocytes after a single 800 mg dose of lithium carbonate and during constant dosing around steady state. Twelve healthy male volunteers took part in the study and took 800 mg of lithium carbonate (Priadel) for 28 days. Le and Lp ranges were determined around steady state using data obtained from eight volunteers known to be compliant. Compliance was measured using electronic monitoring. Both erythrocyte and plasma lithium concentrations reached values comparable to steady state after a single oral dose. This suggests that Le measurements are no better than Lp measurements when attempting to identify noncompliant patients who only dose shortly before a blood test. |
