AN ATTEMPT TO PREDICT DAILY ERYTHROCYTE LITHIUM FLUCTUATIONS

Erythrocyte lithium concentration, which is a better predictor of brai n lithium levels than plasma lithium concentrations, possesses the dis advantage of precise hourly determination following the last intake. T he variability in RBC lithium accumulation increases as the extracellu lar lithium concentration increases. This increase is also time depend ent and it would be very useful if the pharmacokinetic rate constant w ere known. Unfortunately, low lithium levels do not allow measurements within confidence intervals. In this work, we tried to determine, in vitro, the kinetic rate constants in erythrocytes of healthy volunteer s. Different high lithium loaded plasma-like media were used for an ex trapolation procedure of constants allowing the determination of an er ythrocyte load constant namely K-0 = 0.0161 +/- 0.0005 h(-1) at corres ponding plasma lithium concentrations. The abnormalities of lithium tr ansport determined by in vitro procedures would be very useful in unde rstanding the etiology of affective illness. Lithium flux pre-controls corrected with this rate constant would be very helpful in enlarging laboratory time management.