Neuroleptic malignant syndrome during a change from haloperidol to risperidone

To report a case of neuroleptic malignant syndrome (NMS) in a patient whose therapy was being switched from haloperidol to risperidone.

A 57-year-old African-American man, treated for schizophrenia with haloperidol for several years, developed NMS within 48 hours of the addition of low doses of risperidone and mirtazapine to his regimen. Symptoms, which included fever, generalized rigidity, and altered mental status, resolved after discontinuation of psychotropics, supportive management, and several weeks of treatment with bromocriptine and dantrolene. He was subsequently treated with olanzapine without adverse effects.

Several cases of NMS have been reported with risperidone, but none under these circumstances. NMS most likely occurred in this patient as a result of the additive dopamine 2 receptor blocking of haloperidol and risperidone. Sympathetic hyperactivity secondary to mirtazapine may also have been a contributing factor. If NMS may be induced by the simultaneous use of older, high-potency antipsychotics and newer, atypical antipsychotics such as risperidone, switching patients from older to newer antipsychotics may at times be difficult, since completely stopping one antipsychotic before starting the second may place patients at risk for psychotic relapse.

Clinicians should closely monitor patients receiving both haloperidol and risperidone or combinations of similar medications.