Relationship of Prolactin Concentrations to Steady-state Plasma Concentrations of Aripiprazole in Schizophrenia Patients.

BACKGROUND Aripiprazole is regarded as the first-line antipsychotic medication. Long-term aripiprazole therapy can cause hypoprolactinemia, which may result from its activity as a dopamine agonist. However, there is little information on hypoprolactinemia and steady-state aripiprazole concentrations. METHODS The subjects included 66 male and 177 female patients diagnosed with schizophrenia who were treated with aripiprazole. The plasma concentrations of aripiprazole and dehydroaripiprazole and the plasma concentration of prolactin were measured using high-performance liquid chromatography and enzyme immunoassay, respectively. A prolactin concentration of <5 ng/mL was defined as hypoprolactinemia. RESULTS Fifty-two of the 66 male patients (79%) and 58 of the 177 female patients (33%) had hypoprolactinemia. There were significant inverse correlations between plasma prolactin levels and plasma concentrations of aripiprazole (rs = -0.447, p < 0.001) and the active moiety (aripiprazole plus dehydroaripiprazole) (rs = -0.429, p < 0.001) in males. In females, significant inverse correlations were also found between plasma prolactin levels and plasma concentrations of aripiprazole (rs = -0.273, p < 0.01) and the active moiety (rs = -0.275, p < 0.01). CONCLUSIONS These findings suggest that lower prolactin levels are, to some extent, associated with higher plasma drug concentrations in male and female patients with schizophrenia treated with aripiprazole.