Beneficial effects of dantrolene in the treatment of neuroleptic malignant syndrome: a report of two cases.

Two schizophrenic patients developed muscular rigidity, stupor, and hyperpyrexia consistent with neuroleptic malignant syndrome, 8 to 10 days after starting haloperidol therapy. Muscle rigidity was not affected by etybenzatropine or diazepam, but dantrolene, a direct-acting skeletal muscle relaxant, provided muscle relaxation with a concomitant decrease of fever and serum creatine kinase. Neuroleptic malignant syndrome and malignant hyperthermia are clinically similar, and dantrolene is effective in both; suggesting a muscular origin of fever in these two diseases.