Bedside Snapshot
- Use It For
- MH crisis, any age; MH recrudescence and post-crisis prevention; severe NMS rigidity (off-label adjunct)
- Adult Dose
- MH: 2.5 mg/kg rapid IV push, repeat until EtCO₂, HR and rigidity improve (more than 10 mg/kg may be needed)
- Post-crisis: 1 mg/kg IV every 4–6 hr for at least 24 hr
- Pediatric Dose
- Same per-kg dosing as adults (2.5 mg/kg rapid IV push; post-crisis 1 mg/kg every 4–6 hr). Conventional vials: about 7.5 mL/kg per dose
- Onset / Duration
- IV: within minutes / not defined; half-life 4–11 hr
- Do Not Give / Hold If
- No absolute contraindication in MH. No calcium channel blockers (verapamil, diltiazem) during MH. Oral capsules: active liver disease
- Watch For
- Respiratory and swallowing weakness; extravasation at the IV site; fluid overload with conventional vials; recrudescence
- Reversal / Rescue
- No reversal agent. No response by about 10 mg/kg: reconsider the diagnosis. MHAUS hotline 800-644-9737
- Must Remember
- Give it early and keep giving it: 2.5 mg/kg as soon as MH is suspected. Each 20 mg conventional vial needs 60 mL water; call several people to mix, or use Ryanodex (250 mg in 5 mL)
Indications
ED / ICU / Transport
- MH crisis: FDA-labeled for all ages. Give it as soon as MH is suspected after a volatile anesthetic or succinylcholine (see RSI)
- MH recrudescence: rising EtCO₂, heart rate, temperature or rigidity after initial control, mostly in the first 24 hr
- Post-crisis prevention: scheduled IV or oral dosing (FDA-labeled)
- NMS with severe rigidity and hyperthermia: An adjunct to stopping the drug. It is off-label, and the labels say it is not indicated.
Other Uses
- MH prophylaxis: It is FDA-labeled, but not routinely recommended when a trigger-free anesthetic is used.
- Chronic spasticity: oral capsules (spinal cord injury, stroke, cerebral palsy, MS)
- Serotonin syndrome: Not recommended. It failed to prevent death in animal models.
- Heat stroke and other non-MH hyperthermia: It does not help (AHA 2025: 3: No Benefit, B-R adults; 3: No Benefit, C-EO children). An RCT of 52 adults with environmental hyperthermia found no reduction in cooling time.
- MDMA hyperthermia: Usefulness is uncertain (AHA 2025: 2b, C-LD adults; 2b, C-EO children). The data conflict. A 71-case meta-analysis found better survival, and a 9-adult series did not.
MH vs NMS vs Serotonin Syndrome
| Feature | MH | NMS | Serotonin Syndrome |
|---|---|---|---|
| Trigger | Volatile anesthetic or succinylcholine | Antipsychotics (e.g., haloperidol) | Serotonergic combinations (MAOI plus SSRI or SNRI), linezolid, tramadol |
| Onset | Minutes to hours | Days | Hours |
| Muscle findings | Generalized rigidity, rhabdomyolysis | Lead-pipe rigidity, no clonus | Hyperreflexia, clonus, tremor |
| Dantrolene role | First-line antidote | Adjunct for severe rigidity (off-label) | Not recommended |
| Core treatment | Stop trigger, 100% O₂, cool, treat K⁺ and acidosis | Stop drug, supportive care, cooling, benzodiazepines | Stop drug, benzodiazepines, cooling; if above 39 °C with rigidity, agitation or no response to cooling, paralyze and intubate |
Dosing & Administration
Doses vary by protocol; follow local protocols and medical direction.
Available Forms
- Conventional (Dantrium IV, Revonto, generic): 20 mg vial with 3,000 mg mannitol; add 60 mL sterile water (0.33 mg/mL)
- Ryanodex: 250 mg vial with 125 mg mannitol; add 5 mL sterile water (50 mg/mL)
- Oral capsules: 25, 50 and 100 mg; spasticity and follow-up only, never an acute crisis
- MHAUS minimum stock: 36 × 20 mg vials or 3 × 250 mg Ryanodex wherever MH triggers may be given
Adult Dosing
| Indication | Dose & Route | Repeat / Max | Notes |
|---|---|---|---|
| MH crisis: initial | 2.5 mg/kg rapid IV push (actual body weight) | Repeat until EtCO₂, heart rate and rigidity improve. More than 10 mg/kg may be needed (MHAUS) | MHAUS. Differs from FDA label: label cumulative max 10 mg/kg and minimum 1 mg/kg. Differs from EMHG 2024: 2–2.5 mg/kg every 10 min, each dose capped at 300 mg (about 1,200 mg total may be needed). No response by about 10 mg/kg: reconsider the diagnosis. |
| MH recrudescence | Treat as a new crisis: 2.5 mg/kg rapid IV push | No fixed max: titrate to effect | About 20% of 308 patients recrudesce, 80% within 16 hr (MHAUS). Labels: restart at a minimum of 1 mg/kg. |
| Post-crisis maintenance (IV) | 1 mg/kg IV every 4–6 hr | At least 24 hr; then every 8–12 hr once stopping criteria are met | MHAUS. Differs from EMHG 2024: no routine maintenance regimen; redose 2–2.5 mg/kg for recrudescence; each dose capped at 300 mg. |
| Post-crisis follow-up (oral) | 4–8 mg/kg/day PO in 4 divided doses for 1–3 days | Max 8 mg/kg/day | Once swallowing is safe. Boxed hepatotoxicity warning: at 100 kg, 8 mg/kg/day is 800 mg/day or more. Use the lowest effective dose; check LFTs. |
| MH prophylaxis (selected) | Conventional: 2.5 mg/kg IV over about 1 hr, about 75 min pre-op. Ryanodex: over at least 1 min. Oral: 4–8 mg/kg/day in 3–4 doses for 1–2 days | IV: single dose. PO: max 8 mg/kg/day | Labeled, but not routinely recommended: a trigger-free anesthetic is the standard. |
| Chronic spasticity (oral) | 25 mg PO daily, then 25 mg TID, 50 mg TID and 100 mg TID, 7 days per step | Max 100 mg QID (400 mg/day) | Lowest effective dose; stop if no benefit after 45 days (boxed warning). |
| NMS, severe rigidity (off-label) | No labeled dose: per toxicology or specialist consult | — | Case reports and series only. Reulbach 2007 (271 case reports): dantrolene monotherapy had higher mortality; the authors concluded it does not seem to be the evidence-based treatment of choice, though it might help when the premedication was neuroleptic monotherapy. Call a poison center. |
Pediatric Dosing
| Indication | Dose (per kg) & Route | Max Single / Max Total | Notes |
|---|---|---|---|
| MH crisis: initial | 2.5 mg/kg rapid IV push, same as adults | Repeat as needed; no fixed max | Conventional solution about 7.5 mL/kg per dose; Ryanodex about 0.05 mL/kg. |
| Post-crisis maintenance (IV) | 1 mg/kg IV every 4–6 hr | At least 24 hr (MHAUS) | PICU observation for at least 24 hr; watch fluid balance. |
| Chronic spasticity (oral) | 0.5 mg/kg PO daily, then 0.5, 1 and 2 mg/kg TID, 7 days per step | Max 100 mg QID (400 mg/day) | Stop if no benefit after 45 days. Safety under 5 years not established. |
| NMS | Not established in children | — | Specialist or toxicology consult only. |
See weight-based dosing for calculation checks.
Preparation & Administration
- Conventional: 60 mL sterile water for injection (no bacteriostatic agent) per vial; shake until clear. Never NS, D5W or other acidic solutions.
- Diluent and push: stock sterile water in 100 mL vials, not IV bags (MHAUS). Push continuously through a large-bore, ideally dedicated IV; check the site before and during each dose (high pH causes necrosis).
- Stability: use within 6 hr of reconstitution; protect from light. Ryanodex: do not dilute or transfer the suspension to another container. Pool any conventional infusion in a plastic bag, never glass.
- Fluid and mannitol load: each 20 mg vial adds 60 mL water and 3 g mannitol. A 2.5 mg/kg dose delivers about 0.4 g/kg mannitol (conventional vials); account for it before giving more mannitol.
Dosing Notes:
- MH bundle: stop triggers, hyperventilate with 100% O₂ at 10 L/min, call the MHAUS hotline (800-644-9737).
- Hyperkalemia (threshold in Monitoring), MHAUS: calcium chloride 10 mg/kg (max 2,000 mg) or calcium gluconate 10–50 mg/kg (max 3,000 mg); sodium bicarbonate 1–2 mEq/kg; regular insulin 10 units IV with 50 mL D50 (child 0.1 units/kg with 2 mL/kg D25). Details: hyperkalemia.
Contraindications & Precautions
Contraindications
- IV products: none listed; none absolute in a suspected MH crisis.
- Oral capsules: active hepatic disease (hepatitis, cirrhosis); spasticity the patient relies on for posture or balance.
Precautions
- Calcium channel blockers: verapamil and diltiazem with dantrolene have caused hyperkalemia and collapse.
- Neuromuscular disease or limited respiratory reserve: weakness can impair ventilation, cough and swallowing.
- Liver disease: IV hepatotoxicity appears hours to days later; oral risk rises with dose, female sex, age over 35 and estrogens.
- Volume-sensitive patients: conventional vials add large volumes of water and mannitol; pulmonary edema is reported.
- After any dose: walk only with assistance until strength returns; no driving for 48 hr.
Hold / Reassess If
- Failed swallow screen or weak cough: keep NPO and protect the airway
- Swelling, blanching or pain at the IV site: stop and move to another line
FDA Boxed Warning (oral capsules only): fatal hepatitis. The risk is much higher at 800 mg/day or more than at up to 400 mg/day. Monitor liver tests. IV products carry no boxed warning.
Adverse Effects & Toxicity
Common
- Muscle weakness (grip, legs); drowsiness and dizziness up to 48 hr
- Injection-site pain, erythema, swelling and thrombophlebitis (IV)
- Dysphagia and choking; nausea and vomiting
- Flushing: 27% of volunteers with Ryanodex vs 3% with conventional dantrolene
Serious / Life-Threatening
| Effect | Recognition | Management |
|---|---|---|
| Respiratory muscle weakness | Falling tidal volume, weak cough after MH is controlled | Support ventilation; delay extubation until strength returns |
| Aspiration | Coughing or choking with oral intake | Swallow screen before oral intake |
| Extravasation | Swelling, pain, blanching at the IV site | Stop, resite, elevate; institutional protocol |
| Pulmonary edema | Hypoxemia and crackles after large conventional doses | Count water and mannitol in fluid balance; diuretics |
| Hepatotoxicity | Rising ALT and AST days after IV use; jaundice with oral therapy | Check LFTs; stop oral therapy |
| Hyperkalemia and collapse with calcium channel blockers | Peaked T waves, bradycardia, hypotension | Stop the calcium channel blocker; treat hyperkalemia; ACLS |
| Anaphylaxis (rare) | Urticaria, bronchospasm, hypotension | Standard anaphylaxis care |
Overdose & Toxicity Management
- Signs and management: weakness, coma, vomiting, crystalluria. There is no antidote, so the work is airway protection, ventilation, ECG monitoring and generous IV fluids to prevent crystalluria. The value of dialysis is unknown.
Monitoring
| Parameter | When / How Often | Target / Act If |
|---|---|---|
| Clinical: EtCO₂ and temperature | Continuous (core: esophageal or bladder) | EtCO₂ still rising despite hyperventilation: repeat dantrolene. Above 39 °C or rising fast: cool; below 38 °C: stop (MHAUS). EMHG: chilled crystalloid 2,000–3,000 mL; stop cooling at 38.5 °C |
| Clinical: heart rate and ECG | Continuous | Peaked T waves or arrhythmia: check K⁺; avoid calcium channel blockers |
| Clinical: tone, urine, IV site | Before each dose; hourly urine; before each push | Persistent rigidity: redose. Weak grip, cough or swallow: support the airway and keep NPO. Urine below 1 mL/kg/hr or dark: keep diuresis; MHAUS adds sodium bicarbonate infusion 1 mEq/kg/hr. Swelling at the IV site: stop and resite |
| Clinical: limbs | While myoglobinuria or rhabdomyolysis persists | Tense swelling, pain, weak distal pulses: compartment pressures; surgical consult |
| Lab: potassium, glucose, blood gas | Until stable, then every 8 hr; glucose hourly after insulin | K⁺ above 5.9 mEq/L (or lower with ECG changes): treat. Base excess below −8 mEq/L: bicarbonate 1–2 mEq/kg. Low glucose: dextrose |
| Lab: CK, urine myoglobin, creatinine | CK every 8 hr until falling for 24 hr | Rising CK: ongoing MH or rhabdomyolysis. Rising creatinine: acute kidney injury; dialysis may be needed |
| Lab: coagulation, LFTs | Through the crisis and following days | DIC pattern: replace factors. Rising ALT/AST: hepatotoxicity work-up |
| Stopping criteria | ICU or PACU for at least 24 hr | Space doses to every 8–12 hr only when all apply: stable 24 hr, below 38 °C, CK falling, no myoglobinuria, rigidity resolved (MHAUS) |
Interactions & Compatibility
| Drug / Class | Effect | What To Do |
|---|---|---|
| Calcium channel blockers (verapamil, diltiazem) | Marked hyperkalemia and cardiovascular collapse | Do not use in MH. After correcting K⁺ and acidosis, use standard arrhythmia drugs |
| Nondepolarizing blockers (e.g., vecuronium) | Potentiated, prolonged blockade | Monitor neuromuscular function before extubation |
| Sedatives (e.g., midazolam) | Additive CNS depression and weakness | Lower doses; monitor airway |
| Estrogens and hepatotoxic drugs (oral) | Higher hepatitis risk, especially women over 35 | Baseline and periodic LFTs |
| Warfarin, clofibrate, tolbutamide | Altered dantrolene protein binding (reduced by warfarin and clofibrate; increased by tolbutamide) | Clinical significance unclear; monitor response with oral courses |
IV Compatibility
- Conventional solution: sterile water only (see Preparation). Ryanodex may be pushed into a running NS or D5W line.
- Verify with an institutional compatibility resource.
Special Populations
- Pediatrics: The weight-based dose matches the adult dose (see the Pediatric Dosing table). Conventional vials mean a large fluid volume for small children. Count it in fluid balance.
- Pregnancy: It crosses the placenta, and human data are insufficient. Untreated MH can kill both mother and fetus. Never withhold treatment because of pregnancy.
- Lactation: It appears in milk, under 2 mcg/mL with repeat IV dosing. The Ryanodex label says no breastfeeding during treatment and for 3 days after the last dose. The oral capsule label says it should not be used in nursing mothers.
- Older Adults: No specific adjustment, but the weakness raises fall risk.
- Renal Impairment: No adjustment. Don't reduce crisis doses. Track urine output.
- Hepatic Impairment: No IV dose reduction in a crisis. Monitor LFTs.
- Obesity: Dose on actual body weight. The per-dose cap is in the Dosing table.
- MH-Susceptible Families: After an episode, refer for susceptibility testing. Relatives may be at risk.
Field & Transport Considerations
- Scope: Anesthesia, ED, ICU and critical-care transport clinicians give it. Ground EMS rarely carries it, and the rules vary by state and agency protocol. Stocking recommendations cover facilities where MH triggers may be given, succinylcholine-only sites included. An EMS or air-medical RSI program that carries succinylcholine but no dantrolene is counting on fast transport to a hospital that stocks it.
- Where EMS Meets MH: Ambulatory surgery centers call 911, so expect transfers mid-treatment. Ask how much was given. Then ask how much is still coming.
- Storage: vials at 20–25 °C; Ryanodex excursions to 15–30 °C are permitted; protect from light.
- Carried Concentration: One Ryanodex vial holds 12.5 times the drug of a conventional vial. Document in mg/kg, never in vials.
- In Transport: continuous EtCO₂, ECG and core temperature; keep cooling until below 38 °C; no calcium channel blockers.
- Handoff Essentials: trigger agents and exposure time; time and total mg/kg of each dose; EtCO₂ and temperature trend; latest K⁺, CK and urine output.
Clinical Pearls
The mixing bottleneck: A 70 kg adult at 2.5 mg/kg needs 175 mg. That is nine conventional vials and 540 mL of sterile water, every vial mixed by hand. Call several people to mix. Or use Ryanodex: one 5 mL vial.
Earliest MH sign (CCRN, CFRN): rising EtCO₂ even as minute ventilation goes up, with a tachycardia you cannot explain. High fever is a late sign. Don't wait for hyperthermia.
No verapamil or diltiazem: Given with dantrolene, they can cause hyperkalemia and cardiovascular collapse. Correct K⁺ and acidosis first. Then reach for standard arrhythmia drugs.
Plan for the second wave: Recrudescence is common, so plan for it (see Dosing). Keep the patient in an ICU or PACU for at least 24 hr, with dantrolene at the bedside.
Dantrolene is not a paralytic: It works inside the muscle, at the ryanodine receptor. It will not reverse blockade.
Pharmacology
Mechanism of Action
- Ryanodine receptor (RyR1) antagonist: it cuts Ca²⁺ release from the sarcoplasmic reticulum. Less release means less excitation–contraction coupling, so rigidity and heat production fall.
- Not MH-selective: Normal Ca²⁺ release gets dialed down too, which is why therapeutic doses cause weakness. The cardiac RyR2 is relatively spared.
Pharmacokinetics
- Onset: IV within minutes (Ryanodex plasma peak by 1 min); oral dosed 4 times daily.
- Half-life: IV 4–8 hr (conventional label); 8.5–11.4 hr (Ryanodex studies); oral 8.7 hr after 100 mg.
- Metabolism: hepatic, to 5-hydroxydantrolene. Elimination: urine; crystalluria possible in overdose.
Names & Classification
- Generic Name
- Dantrolene sodium
- Brand Names
- Dantrium Intravenous and Revonto (20 mg vials); Ryanodex (250 mg vial); Dantrium capsules; generic injection and capsules
- Pharmacologic Class
- Ryanodine receptor (RyR1) antagonist; hydantoin derivative
- Therapeutic Class
- Direct-acting skeletal muscle relaxant; malignant hyperthermia antidote
- Look-Alike / Sound-Alike
- No name pair; the practical error is confusing 20 mg vials (0.33 mg/mL) with 250 mg Ryanodex vials (50 mg/mL)
References
- Par Health. (2025). DANTRIUM Intravenous (dantrolene sodium for injection): Prescribing information (revised 12/2025). DailyMed. DailyMed label
- Eagle Pharmaceuticals. (2024). RYANODEX (dantrolene sodium) for injectable suspension: Prescribing information (revised 4/2024). DailyMed. DailyMed label
- Par Health. (2026). DANTRIUM (dantrolene sodium) capsules: Prescribing information, including boxed warning (revised 07/2026). DailyMed. DailyMed label
- Malignant Hyperthermia Association of the United States (MHAUS). Managing an MH crisis: Acute crisis protocol. No date shown on the page; retrieved October 15, 2026. MHAUS page
- Malignant Hyperthermia Association of the United States (MHAUS). (2017). Dantrolene administration after an MH event (MHAUS recommendation; recrudescence in 20% of 308 patients, citing Burkman JM, Posner KL, Domino KB. Anesthesiology 2007;106:901-906). MHAUS page
- Glahn, K. P. E., et al. (2025). Recognition and management of a malignant hyperthermia crisis: Updated 2024 guideline from the European Malignant Hyperthermia Group. British Journal of Anaesthesia, 134(1), 221–223. DOI
- Klincová, M., et al. (2022). Malignant hyperthermia in PICU: From diagnosis to treatment in the light of up-to-date knowledge. Children, 9(11), 1692. DOI
- Chiew, A. L., & Isbister, G. K. (2025). Management of serotonin syndrome (toxicity). British Journal of Clinical Pharmacology, 91(3), 654–661. DOI
- Malignant Hyperthermia Association of the United States (MHAUS). What should be on an MH cart? No date shown on the page; retrieved October 15, 2026. MHAUS page
- Malignant Hyperthermia Association of the United States (MHAUS). Post acute phase management in PACU or ICU. No date shown on the page; retrieved October 15, 2026. MHAUS page
- American Heart Association. (2025). 2025 American Heart Association Guidelines for CPR and ECC, Part 10: Adult and pediatric special circumstances of resuscitation (hyperthermia). AHA page
- Reulbach, U., et al. (2007). Managing an effective treatment for neuroleptic malignant syndrome. Critical Care, 11(1), R4. DOI
Medical Disclaimer
- For Educational Purposes Only: This content is intended for educational reference and should not be used for clinical decision-making.
- Not a Substitute for Professional Judgment: Always consult your local protocols, institutional guidelines, and supervising physicians.
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