Effect of antipsychotics on serum lithium levels and white blood cell counts

Abstract Lithium carbonate is used to increase white blood cell counts as a means of counteracting leukopenia caused by the administration of antipsychotic drugs. To evaluate the effect of antipsychotics on the leukocyte‐enhancing effect of lithium, we compared white blood cell counts, serum lithium levels, and lithium dosage in patients receiving antipsychotics and lithium in combination and patients receiving lithium alone. Chlorpromazine equivalent values were used as an indicator of the antipsychotic dose. Lithium serum levels were measured in 41 hospitalized patients. The lithium dose in the combination group (median, 800 mg) was significantly higher than that in group receiving only lithium (median, 400 mg) (P = 0.03). The lithium doses in the combination group receiving ≥1000 mg chlorpromazine equivalents (overdosing; median lithium dose 800 mg) and the combination group treated with 600‐999 mg chlorpromazine equivalents (high dosing; median lithium dose 800 mg) were significantly higher than the group that was not treated with antipsychotic medication, with median lithium dose 400 mg (P < 0.05).There were no significant differences in the white blood cell counts and serum lithium levels. Because of the large variety of antipsychotic drugs used in combination with lithium and the various doses used, it was difficult to evaluate the effects of lithium, with or without antipsychotic administration, on leukocyte count enhancement. We are planning to study a larger number of patients and, since renal function could not be assessed in this study, we will also focus on renal function, including urine output.