Relationship of Prolactin Concentrations to Steady-State Plasma Concentrations of Aripiprazole in Patients With Schizophrenia

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 men. In women, 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.

Effect of adjunctive treatment with aripiprazole to atypical antipsychotics on cognitive function in schizophrenia patients

Second-generation antipsychotics yield only a modest improvement in cognitive benefit compared to first-generation antipsychotics. Aripiprazole, which is a partial dopamine D2 receptor agonist, may have an impact on cognitive dysfunction in patients with schizophrenia. This study administered aripiprazole or placebo to 36 outpatients with schizophrenia also receiving risperidone or olanzapine for 12 weeks in a double-blind, randomized, placebo-controlled study. Cognitive function was evaluated using the Brief Assessment of Cognition in Schizophrenia (BACS) just prior to drug administration as well as 12 weeks after. The PANSS and UKU side effect rating scales were used to evaluate the clinical response to additional treatment with aripiprazole. In a primary analyses, ANCOVA showed that there was an interaction between the treatment group and time for verbal fluency (p < 0.05), but not for any domain in BACS, PANSS or UKU side effect rating scales. Upon secondary analysis, however, the ameliorative change in motor speed as assessed by the BACS (p < 0.05) for those receiving aripiprazole was greater than that for the placebo group, whereas deterioration in verbal fluency (p < 0.01) and executive function (p < 0.01) in those receiving aripiprazole was significantly greater than in the placebo group. These results suggest that adjunctive treatment with aripiprazole improves motor speed but worsens some cognitive functions. It is likely that these effects are due to the dopamine D2 antagonistic effect of aripiprazole.

Dose-dependent effects of adjunctive treatment with aripiprazole on hyperprolactinemia induced by risperidone in female patients with schizophrenia

Hyperprolactinemia is a frequent consequence of treatment with risperidone. Recent studies have suggested that aripiprazole, a partial dopamine agonist, reduces the prolactin response to antipsychotics. Thus, we examined the dose effects of adjunctive treatment with aripiprazole on the plasma concentration of prolactin in patients who had elevated prolactin levels because of risperidone treatment. Aripiprazole was concomitantly administrated to 16 female patients with schizophrenia receiving 2 to 15 mg/d of risperidone. Dosages of aripiprazole were gradually increased from 3 to 12 mg/d with 2- to 4-week intervals. Sample collections for prolactin were conducted before aripiprazole administration (baseline) and 2 to 4 weeks after the dose escalation of aripiprazole and just before next dose escalation. The samples were taken just before the morning dose. The plasma concentration of prolactin during aripiprazole administration (3, 6, 9, or 12 mg/d) was significantly lower than that at baseline. The mean (±SD) percent reductions at 3, 6, 9, and 12 mg/d were 35% ± 14%, 54% ± 17%, 57% ± 19%, and 63% ± 17%, respectively. However, neither the plasma concentration of prolactin nor the reduction ratio differed among the dosages of 6, 9, and 12 mg/d of aripiprazole. Three out of 8 patients with amenorrhea improved after 12 mg/d of aripiprazole. The present study suggests that adjunctive treatment with aripiprazole reduces the prolactin concentration that had been increased because of risperidone treatment. The effect occurs even when a low dosage (3 mg/d) of aripiprazole was used and achieves a plateau at dosages beyond 6 mg/d.