Rigidity caused dantrolene

Dantrolene is not likely to be effective for hyperthennia caused by conditions other than muscular hyperactivity, such as increased metabolic rate (eg, salicylate or dinitrophenol poisoning), neuroleptic malignant syndrome (NMS), impaired heat dissipation (eg, anticholinergic syndrome), or environment exposure (heat stroke). However, there is anecdotal evidence (case reports or case-control studies) of benefit for the management of NMS, MAO inhibitor (phenelzine poisoning)-induced hyperthermia, muscle rigidity from baclofen withdrawal, hypertonicity from carbon monoxide poisoning, tetanus, and black widow spider envenomation. 

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