Dantrolene Dosing for MH – Arun Anaesthesia Academy

Dantrolene Dosing for MH

Arun Anaesthesia Academy

As per EMHG 2024 & MHAUS guidelines

Emergency protocol — Malignant hyperthermia

Call for help — get the MH kit and dantrolene
Stop volatile agents and suxamethonium
Hyperventilate with 100% O₂ at high fresh gas flow (≥10 L/min)
Insert activated charcoal filters if available
Switch to TIVA — inform surgeon to finish quickly
Give dantrolene as calculated below
Start active cooling if temperature >39°C

1

Weight & Formulation

Dantrolene is dosed on actual body weight, up to a maximum of 300 mg per dose (EMHG) — no dose cap (MHAUS).

Dantrium / Revonto

Ryanodex

kg

Weight should be 1–250 kg.

Reconstitution — each vial

20mg

dantrolene

+

60mL

sterile water

=

0.33

mg/mL

Enter patient weight above to calculate dantrolene doses.

Steps

Full Protocol

2

Treatment Steps (Dantrolene)

i

Prophylaxis (Pre-operative)

Not recommended by MHAUS — MH-susceptible patients can be safely anaesthetised with a trigger-free technique

Manufacturer label dosing, if used:

3

Concurrent Emergency Management

A
Remove trigger & ventilate
- Stop volatile agents and suxamethonium
- 100% O₂ at high fresh gas flow (≥10 L/min)
- Insert activated charcoal filters if available
- Hyperventilate — increase minute ventilation 2–3 times to normalise ETCO₂
- Maintain anaesthesia with TIVA
- Do not waste time changing the machine or circuit
B
Active cooling
- Cool if core temperature >39°C or rising rapidly
- Cold IV saline
- Surface cooling — ice packs to groin, axillae, neck
- Cold body-cavity lavage if open
- Refrigerated IV fluid 20 mL/kg (up to about 3 L in adults) if external cooling is not enough
- Stop cooling once <38.5°C (EMHG) / <38°C (MHAUS) to avoid hypothermia
C

Hyperkalaemia (K⁺ >5.9 or ECG changes)
D
Arrhythmias
- Treat with standard ACLS drugs
- Avoid calcium channel blockers — with dantrolene they may cause hyperkalaemia and cardiovascular collapse
- Arrhythmias usually settle once acidosis and hyperkalaemia are corrected
E
Monitor, investigate & refer
- Core temperature, ABG, K⁺, CK, myoglobin, coagulation
- pH, lactate, K⁺ and CK every 8 hrs until CK falling
- Check the IV site for thrombophlebitis or extravasation
- Urine output >2 mL/kg/hr (EMHG) / >1 mL/kg/hr (MHAUS) — watch for rhabdomyolysis and DIC
- Admit to ICU for at least 24 hrs
- Refer patient and family to an MH testing centre
- Report to MHAUS / NAMHR or national MH registry

i

Signs of Malignant Hyperthermia

RespiratoryRising ETCO₂ / hypercarbia despite increased ventilation, tachypnoea, rapid CO₂ absorber exhaustion
CardiacUnexplained tachycardia, arrhythmias
MuscularMasseter spasm, generalised muscle rigidity
MetabolicMixed respiratory and metabolic acidosis, central venous desaturation
SkinCyanosis, mottling
LateRising temperature (often a late sign), hyperkalaemia, rising CK, myoglobinuria, DIC

Sources: Revonto prescribing information; MHAUS; EMHG 2024

i

Differential Diagnosis

AnaestheticInadequate anaesthesia or analgesia, hypoventilation, exhausted CO₂ absorbent, CO₂ insufflation
EndocrineThyroid storm, phaeochromocytoma
InfectiveSepsis
Drug-inducedNeuroleptic malignant syndrome, serotonin syndrome, anticholinergic toxicity, MDMA / cocaine
OtherIatrogenic overheating, hypoxic brain injury

If >10 mg/kg dantrolene without response — reconsider the diagnosis

i

Dantrolene — Side Effects

MuscularSkeletal muscle weakness — may impair ventilation and swallowing after extubation. Care with meals. No driving for up to 48 hrs
LocalHighly alkaline (pH ~9.5 Dantrium / Revonto, ~10.3 Ryanodex) — thrombophlebitis and tissue necrosis on extravasation. Use a large-bore IV
RenalOsmotic diuresis from mannitol (3 g per 20 mg Dantrium vial) — catheterise. Ryanodex has only 125 mg per vial
InteractionCalcium channel blockers (verapamil, diltiazem, amlodipine, nicardipine) — contraindicated with IV dantrolene: marked hyperkalaemia, cardiovascular collapse
DrugsPotentiates neuromuscular block (vecuronium). Additive CNS and respiratory depression with opioids, sedatives, antipsychotics and anxiolytics. CYP3A4 inducers lower levels, inhibitors raise them
Fluid loadPulmonary oedema reported during MH treatment — diluent volume and mannitol contribute. Dantrium / Revonto needs 60 mL per vial (over 500 mL per bolus in adults) — watch fluid balance
SeriousRespiratory depression, pulmonary oedema, pleural effusion with eosinophilia, aplastic anaemia, heart failure, anaphylaxis
PregnancyCrosses placenta — do not withhold in an MH crisis. Avoid breastfeeding during treatment and for 3 days after the last dose
OtherFlushing (27% with Ryanodex), drowsiness and dizziness up to 48 hrs, dysphonia, dysphagia, nausea, blurred vision. Hepatotoxicity with prolonged oral use — risk higher above 800 mg/day

Sources: MHAUS; EMHG 2024; Medscape — Dantrolene; Revonto and Ryanodex prescribing information