To the Editor: We report herein, what is, to our knowledge, the first case of neuroleptic malignant syndrome (NMS) related to blonanserin.

A 30-year-old woman with a diagnosis of mental retardation and with profound intellectual impairment (IQ<45) was admitted to a psychiatric hospital for the first time because of insomnia, psychomotor agitation, monologue, and persecutory delusions. After a 7-day period of medication withdrawal, blonanserin, 8 mg/day, was introduced for psychiatric symptoms such as emotional agitation, auditory hallucinations, and delusions. Her disturbed behavior with high agitation was slightly improved by the medication. After treatment with blonanserin for 7 days, the patient had a high fever (100.4°F) and was obtunded with muscle rigidity. She had a high pulse rate (104 bpm), and an elevated leukocyte level (8.5×109/liter), with extrapyramidal symptoms and perspiration. The patient was suspected to be developing NMS. Blonanserin was discontinued, and the patient received diazepam treatment. The next day, the fever disappeared and the serum leukocyte level was normalized (5.7∼5.9×109/liter). The possibility of infectious disease was excluded since the level of C-reactive protein was within the normal range and all the symptoms disappeared rapidly after treatment for neuroleptic malignant syndrome.

This case report shows that neuroleptic malignant syndrome can occur after the introduction of blonanserin treatment. Blonanserin is a novel dopamine-serotonin antagonist with potent dopamine D₂ and serotonin 5HT₂ antagonist properties.¹ Because of the receptor binding profile and pharmacological property of blonanserin, side effects such as extrapyramidal symptoms tend to occur less often with blonanserin than haloperidol.² This patient had not been medicated with antipsychotic drugs before. Another important issue to be mentioned in this case is mental retardation, which is one of the risk factors for neuroleptic malignant syndrome.³ Several other risk factors should be taken into account in cases involving mentally retarded patients, whose symptoms often include dehydration, agitation, malnutrition, and exhaustion. Special caution with regard to patients who have risk factors for neuroleptic malignant syndrome is therefore necessary when starting to administer antipsychotic drugs.