Dantrolene sodium, sold under the brand name Dantrium among others, is a postsynaptic muscle relaxant that lessens excitation-contraction coupling in muscle cells. It achieves this by inhibiting Ca²⁺ ions release from sarcoplasmic reticulum stores by antagonizing ryanodine receptors. It is the primary drug used for the treatment and prevention of malignant hyperthermia, a rare, life-threatening disorder triggered by general anesthesia or drugs. It is also used in the management of neuroleptic malignant syndrome, muscle spasticity (e.g. after strokes, in paraplegia, cerebral palsy, or patients with multiple sclerosis), and poisoning by 2,4-dinitrophenol or by the related compounds dinoseb and dinoterb.

The most frequently occurring side effects include drowsiness, dizziness, weakness, general malaise, fatigue, and diarrhea.

It is marketed by Par Pharmaceuticals LLC as Dantrium (in North America) and by Norgine BV as Dantrium, Dantamacrin, or Dantrolen (in Europe). A hospital is recommended to keep a minimum stock of 36 dantrolene vials totaling 720 mg, sufficient for a 70-kg person.

Oral dantrolene is contraindicated for

There are no contraindications for intravenous dantrolene used for prophylaxis or management of malignant hyperthermia.

If needed in pregnancy, adequate human studies are lacking, therefore the drug should be given in pregnant women only if clearly indicated. It may cause hypotonia in the newborn if given closely before delivery.

Dantrolene may interact with the following drugs:

Dantrolene depresses excitation-contraction coupling in skeletal muscle by acting as a receptor antagonist to the ryanodine receptor, and decreasing free intracellular calcium concentration.