Serum Lithium Levels: Ideal Time for Sample Collection! Are We Doing it Right?

Lithium has been the gold standard drug for bipolar disorders. The efficacy of lithium is dose-dependent and reliably correlates with that of serum lithium levels (trough levels). Trough levels are best measured when tested just before the next dose. In clinical practice, when lithium was administered in divided doses, trough levels were measured at 12 h after the last dose. Does this practice of 12 h lithium estimation apply to once a day (OD) administration of lithium also? This study was undertaken to test this hypothesis. Serum lithium levels were measured at 12 and 24 h post the last dose in 48 patients taking an OD dosing of sustained preparations of lithium. The mean and (standard deviation) of serum lithium levels at 12 h (0.82 [0.29]) and at 24 h (0.60 [0.20]) were calculated. The serum lithium level at 12 h was 1.3 times higher than that of the 24 h levels (actual trough levels). Thus, it seems appropriate to estimate the serum lithium levels (trough levels) at 24 h post the last dose in patients taking lithium as an OD dosage, which may prevent patient maintained on a lower than required dose of lithium.