Successful Treatment With Blonanserin for Drug-Induced Hyperprolactinemia in Chronic Schizophrenia Patients: A Six-Month Follow-Up of Two Cases

“Ms. I,” A 53-year-old woman with schizophrenia (DSM-IV-TR) had been hospitalized several times. Her first psychotic episode, including disorganized speech, auditory hallucinations, and delusions, occurred at the age of 17. Because she had menstrual irregularities, her blood sample was taken, disclosing serum PRL levels of 114.8 ng/ml. As she was taking risperidone 5 mg per day, risperidone-induced hyperprolactinemia was suspected. Subsequently, risperidone was tapered and ceased while, instead, blonanserin was cross-titrated up to 24 mg per day for 4 weeks. The characteristics and changes in serum PRL levels are shown in Table 1.

“Mr. M,” A 41-year-old man with schizophrenia (DSM-IV-TR) presented with his first psychotic episode, characterized by auditory hallucinations, delusions, irritability, and aggression, at the age of 21. He complained of ejaculation disorder and took a blood test, revealing that serum PRL levels were 51.5 ng/ml. Risperidone 6 mg was then tapered and ceased while blonanserin started to be cross-titrated up to 24 mg per day for 4 weeks. His sexual dysfunction was improved, but he presented with irritability and aggression. Sodium valproate increased to 800 mg relieved these symptoms. The characteristics and changes in serum PRL levels are shown in Table 1.

PRL is released from lactotrophic cells in the anterior pituitary, and its secretion is regulated by PRL-releasing factor (PRF) and PRL-inhibiting factor (PIF).¹ The regulation of PRL secretion is mainly affected by dopamine, one of the PIFs.¹ Blonanserin has a high affinity for dopamine D_2,3 and serotonin 5-HT_2A receptor subtypes, whose affinity is higher for D₂ receptors than for 5-HT_2A receptors, compared with that of risperidone, while blonanserin has low or very low affinity for all other neurotransmitter receptors.² Several studies in rats and humans have shown a correlation between the serum PRL levels and the penetrability of antipsychotics across the blood–brain barrier.^3,4 Antipsychotics need to pass across the blood–brain barrier to ameliorate the psychotic symptoms, whereas the anterior pituitary is outside the blood–brain barrier and is accessible to antipsychotics.^1,3 Therefore, antipsychotics such as risperidone, with a lower penetrability across the blood–brain barrier may cause higher plasma PRL levels.^3,4 Blonanserin has been shown to have a high affinity for D₂ receptors² as well as a potentially high penetrability of the blood–brain barrier.⁵ The two schizophrenic patients with risperidone-induced hyperprolactinemia presented herein were improved by switching to blonanserin. The findings in these case reports suggest that blonanserin, with a potentially high penetrability of the blood–brain barrier, might be one of the treatment options for drug-induced hyperprolactinemia. To test the efficacy, it would need a well-designed study in a larger sample size.