The effect of concomitant use of neuroleptic drugs and lithium on the erythrocyte/plasma lithium ratio in Iranian patients with bipolar disorder.

Patients treated with lithium (Li+) and neuroleptic drugs concomitantly are reported to show more pronounced adverse effects than patients on Li+ alone. There are conflicting results about the effect of neuroleptic drugs on the erythrocyte/plasma Li+ ratio and intraerythrocyte Li+ concentration, and methodological problems may be a reason for this. The effect of the concurrent use of neuroleptic drugs with Li+ on the Li+ ratio was studied in 66 patients with bipolar affective disorders during prophylactic Li+ therapy using the new direct method of measuring erythrocyte Li+ concentration. This new direct method has been shown to give much more precise and accurate results than the values obtained by other methods. No relationship was found between the Li+ ratio and sex, age, Li+ dosage, duration of treatment or plasma Li+ concentration. Results revealed that patients taking a combination of Li+ and neuroleptic drugs showed significantly lower Li+ ratios and intraerythrocyte Li+ concentrations as compared with those on Li+ alone. It is notable that this reducing effect of neuroleptic drugs was increased by the concurrent use of two types of neuroleptic drugs. The effect on neuroleptic drugs on the Li+ ratio may be mediated through a stabilizing effect of these drugs on the cell membrane and consequently Li+ transport in erythrocytes.