Dantrolene
Skeletal muscle relaxants and spasmolytics
Skeletal muscle relaxants and spasmolytics
Relaxes skeletal muscle from inside the fibre by blocking calcium release. Given intravenously, it is the specific treatment of malignant hyperthermia.
Also called: Dantrolene sodium
Quick facts
- Group
- Skeletal muscle relaxants and spasmolytics
- Target
- Ryanodine receptor 1 (RyR1), the calcium-release channel of the sarcoplasmic reticulum
- Used for
- Malignant hyperthermia
- Key effects
- Muscle weakness · Drowsiness · Diarrhoea
- Monitor
- Liver tests · In a crisis
- ATC
- M03CA01
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows dantrolene bound to a cytoplasmic domain (RY12) of rabbit RyR1; the human channel is very similar.
Dantrolene acts beyond the neuromuscular junction, on the muscle itself. It inhibits the ryanodine receptor RyR1 and so reduces calcium release from the sarcoplasmic reticulum, uncoupling excitation from contraction; fast fibres are affected most. In malignant hyperthermia, triggering anaesthetics cause uncontrolled calcium release through abnormal RyR1 channels; intravenous dantrolene stops this hypermetabolic state.
- Dantrolene binds RyR1 in the sarcoplasmic reticulum
- Less calcium is released into the muscle fibre
- Excitation is uncoupled from contraction
- Muscle relaxes; in malignant hyperthermia the crisis stops
Indications
- Malignant hyperthermia: treatment of the crisis (IV) and prevention in susceptible patients Malignant hyperthermia →
- Chronic spasticity from spinal cord injury Spinal cord injury →
- Chronic spasticity from multiple sclerosis Multiple sclerosis →
- Chronic spasticity from cerebral palsy Cerebral palsy →
- Chronic spasticity after stroke Ischaemic stroke →
- Neuroleptic malignant syndrome (off-label) Neuroleptic malignant syndrome →
Adverse effects
Common
- Muscle weakness (loss of grip strength, weak legs)
- Drowsiness, dizziness and general fatigue
- Diarrhoea
- Pain, redness or phlebitis at the infusion site
- Possible photosensitivity
Contraindications
- Active liver disease (hepatitis, cirrhosis), for oral use
- When spasticity is needed to keep posture, balance or function
Key interactions
- Calcium channel blockers (e.g., verapamil) during a malignant hyperthermia crisis
- Marked hyperkalaemia and cardiovascular collapse; the combination is avoided
- Other potentially hepatotoxic medicines
- Higher risk of liver injury with oral dantrolene
What is monitored
- Liver tests (AST/ALT, alkaline phosphatase, bilirubin) at baseline and regularly during oral treatment
- In a crisis: temperature, heart rate and rhythm, acid-base status and potassium
- Vital signs and breathing after IV use (muscle weakness)
- Oral use is stopped if no benefit is seen after about 45 days
Administration and safety
- IV vials are reconstituted only with sterile water for injection without bacteriostatic agent; dextrose, saline and other acidic solutions are incompatible
- The solution is very alkaline: a secure line is used and extravasation is avoided
- Each vial contains mannitol, which counts when mannitol is also given for the kidneys
- Operating rooms that use triggering anaesthetics keep dantrolene immediately available
Pregnancy and breastfeeding
There are no adequate studies in pregnancy; animal studies showed harm at high doses. In a malignant hyperthermia crisis, the benefit is weighed against the risk.
Nursing care
- Know the signs of malignant hyperthermia after triggering anaesthetics: muscle rigidity, rapidly rising temperature, tachycardia and metabolic acidosis
- Several staff are often needed to reconstitute many vials quickly
- Check the IV site often for pain, swelling and leakage
- After IV doses, warn about weakness (stairs, walking) and drowsiness
- With oral use, teach the signs of hepatitis (jaundice, dark urine, nausea) and sun protection
Pharmacokinetics
- Absorption
- Oral absorption is incomplete and slow but consistent
- Metabolism
- Liver (5-hydroxy and acetamido metabolites)
- Half-life
- About 9 hours by mouth; about 4 to 8 hours after intravenous use
Test yourself
Think of the answer, then tap the question to see it.
Where does dantrolene act?
On the ryanodine receptor RyR1 of the sarcoplasmic reticulum, inside skeletal muscle (not at the neuromuscular junction).
Which emergency is dantrolene the specific treatment for?
Malignant hyperthermia triggered by volatile anaesthetics or succinylcholine.
Which drug class should not be combined with IV dantrolene in a crisis?
Calcium channel blockers such as verapamil (hyperkalaemia and cardiovascular collapse).
What is the main risk of long-term oral dantrolene?
Hepatotoxicity, so liver tests are monitored.
Which diluent is used to reconstitute IV dantrolene?
Sterile water for injection without bacteriostatic agent.
Connections
← Back to the class: Skeletal muscle relaxants and spasmolytics
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - DANTROLENE injection, powder, for solution (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - DANTROLENE SODIUM capsule (DailyMed (U.S. National Library of Medicine), 2026); Dantrolene: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026).
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Representative model, for educational purposes only.