Last reviewed 2026-05-13 · How we verify

Ryanodex (DANTROLENE)

Ryanodex (Dantrolene) is a small molecule skeletal muscle relaxant developed by PAR Sterile Products and currently owned by Ph Health. It targets the ryanodine receptor 1 to treat malignant hyperthermia, muscle spasticity of cerebral and spinal origin, and spasticity. FDA approved in 1974, it is now off-patent with multiple generic manufacturers. Key safety considerations include its potential for hepatotoxicity and the need for careful monitoring. Ryanodex has a half-life of 10 hours and bioavailability of 70%.

At a glance

Approved indications

• Malignant Hyperthermia Prevention
• Malignant hyperthermia
• Muscle Spasticity of Cerebral Origin
• Muscle spasticity of spinal origin
• Spasticity

Boxed warnings

• Dantrolene sodium has a potential for hepatotoxicity, and should not be used in conditions other than those recommended. Symptomatic hepatitis (fatal and non-fatal) has been reported at various dose levels of the drug. The incidence reported in patients taking up to 400 mg/day is much lower than in those taking doses of 800 mg or more per day. Even sporadic short courses of these higher dose levels within a treatment regimen markedly increased the risk of serious hepatic injury. Liver dysfunction as evidenced by blood chemical abnormalities alone (liver enzyme elevations) has been observed in patients exposed to dantrolene sodium for varying periods of time. Overt hepatitis has occurred at varying intervals after initiation of therapy, but has been most frequently observed between the third and twelfth month of therapy. The risk of hepatic injury appears to be greater in females, in patients over 35 years of age, and in patients taking other medication(s) in addition to dantrolene sodium . Spontaneous reports suggest a higher proportion of hepatic events with fatal outcome in elderly patients receiving dantrolene sodium . However, the majority of these cases were complicated with confounding factors such as intercurrent illnesses and/or concomitant potentially hepatotoxic medications (see Geriatric Use subsection). Dantrolene sodium should be used only in conjunction with appropriate monitoring of hepatic function including frequent determination of SGOT or SGPT. If no observable benefit is derived from the administration of dantrolene sodium after a total of 45 days, therapy should be discontinued. The lowest possible effective dose for the individual patient should be prescribed.

Common side effects

• Pulmonary edema
• Thrombophlebitis
• Tissue necrosis
• Urticaria
• Erythema
• Anaphylaxis
• Injection site reactions
• Hepatitis
• Seizures
• Pleural effusion with pericarditis
• Aplastic anemia
• Leukopenia

Key clinical trials

• Targeting Residual Activity By Precision, Biomarker-Guided Combination Therapies of Multiple Sclerosis (TRAP-MS) (PHASE1,PHASE2)
• A Clinical Trial Utilizing Dantrolene in Patients With Ventricular Arrhythmias. (PHASE2,PHASE3)
• Dantrolene in Statin-induced Myopathy (PHASE2,PHASE3)
• Study of Human Non-Shivering Thermogenesis and Basal Metabolic Rate (PHASE2)
• The Use of Dantrolene to Improve Analgesia in Posterior Lumbar Surgery (PHASE2)
• A Clinical Trial of Dantrolene Sodium in Pediatric and Adult Patients With Wolfram Syndrome (PHASE1,PHASE2)
• Efficacy and Safety of Ryanodex® (EGL-4104) as Adjuvant Treatment in Subjects With Exertional Heat Stroke (EHS) (PHASE2)
• Study to Assess the Efficacy and Safety of Ryanodex as Adjuvant Treatment in Subjects With EHS (PHASE3)

Primary sources

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Competitive intelligence

For the full competitive landscape — auto-detected comparators, recent regulatory actions across the set, upcoming PDUFA, patent timeline, sponsor landscape:

• Ryanodex CI brief — competitive landscape report
• Ryanodex updates RSS · CI watch RSS
• Ph Health portfolio CI