Which medication can be used in the treatment of neuroleptic malignant syndrome?

Dantrolene sodium is the correct choice for treating neuroleptic malignant syndrome (NMS), a potentially life-threatening condition characterized by severe muscle rigidity, hyperthermia, autonomic instability, and altered mental status that occurs as a reaction to antipsychotic medications. Dantrolene works by directly interfering with muscle contraction by inhibiting calcium release from the sarcoplasmic reticulum in skeletal muscle. This action helps decrease muscle rigidity and hyperthermia associated with NMS.

The other options may have roles in different contexts but are not appropriate for treating NMS. Amantadine, for instance, is primarily used for Parkinson's disease and drug-induced extrapyramidal symptoms but does not address the primary issues of NMS. Haloperidol is an antipsychotic medication that, while capable of causing NMS, would not be used to treat the syndrome itself. Procyclidine is an anticholinergic agent often used to treat extrapyramidal symptoms associated with antipsychotics but similarly does not target the specific pathophysiology of NMS. Thus, dantrolene sodium stands out as the appropriate therapeutic agent in the context of neuroleptic malignant syndrome.