A muscle relaxant

Dantrolene

A muscle relaxant for long-term severe muscle stiffness, and the hospital treatment for a rare anaesthetic emergency.

What is Dantrolene?

Dantrolene is a muscle relaxant used to ease severe, long-standing muscle stiffness and spasticity, for example after a stroke or spinal injury or in cerebral palsy and multiple sclerosis. It is also the emergency hospital medicine for malignant hyperthermia, a rare dangerous reaction to certain anaesthetics. It works directly on muscle to reduce excessive contraction. Liver function is monitored because it can occasionally harm the liver.

Education and reference only. This is a plain-language guide to Dantrolene — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.

Written by Meds Global Health Clinical Team · Clinically reviewed by Dr Muhammad Suffyan, MB BS, Founder & Clinical Director · Last reviewed · How we review
Class: Muscle relaxants → Brands: Dantrium
Dantrolene (Muscle relaxants) — Meds Global Health reference card with 2D molecular structure
Dantrolene — Muscle relaxants. The image shows the active ingredient's 2D molecular structure.

What it is

Dantrolene is a muscle relaxant that works directly on muscle to reduce severe stiffness and spasticity from conditions such as stroke, spinal cord injury, cerebral palsy and multiple sclerosis. Unlike most muscle relaxants that act mainly on the nervous system, it acts on the muscle itself. It is also the key emergency treatment, given in hospital, for malignant hyperthermia — a rare but dangerous reaction to certain general anaesthetics.

How it works

Dantrolene reduces the release of calcium inside muscle cells, which is the signal that makes muscle fibres contract. With less calcium released, the muscle contracts less forcefully, easing spasticity and stiffness. In malignant hyperthermia this same action calms the dangerous, runaway muscle activity and overheating.

Company & origin

Originated / developed by: Norwich Eaton (originator).

A muscle relaxant used in the UK for chronic severe spasticity and as the emergency treatment for malignant hyperthermia.

Practical use

How to take Dantrolene

General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.

  • Take it regularly as prescribed, usually starting low and increasing slowly over weeks to find the right level.
  • Be aware it commonly causes drowsiness and muscle weakness, so take care with driving and machinery until you know how it affects you.
  • Attend for the liver blood tests your team arranges, and report yellowing of the skin or eyes, dark urine or unusual tiredness.
  • Do not stop suddenly without advice; your team may reduce it gradually or review whether it is helping.
  • If you miss a dose, take it when you remember unless it is nearly time for the next, then skip the missed one — do not double up.

Weighing it up

Advantages & disadvantages of Dantrolene

Advantages

  • Acts directly on muscle, so it can help spasticity with somewhat less sedation than some alternatives.
  • Provides an option for severe, long-standing stiffness that limits movement or care.
  • Is the established, life-saving emergency treatment for malignant hyperthermia.

Disadvantages

  • Can harm the liver, so regular liver blood tests are needed.
  • Commonly causes drowsiness and muscle weakness, which can be limiting.
  • Often needs a slow, careful build-up and may be stopped if it does not clearly help.

Practical use

Good to know

For long-term spasticity, dantrolene is usually started low and built up slowly over weeks to find the level that helps stiffness without causing too much weakness. Because it can affect the liver, liver blood tests are checked before and during treatment, and it is stopped if there is no clear benefit after a reasonable trial. Report any yellowing of the skin or eyes, dark urine, persistent nausea or unusual tiredness, as these can signal liver problems. It commonly causes drowsiness and muscle weakness, so take care with driving and tasks needing alertness until you know how it affects you.

Who should not take it / use with caution

  • People with active liver disease or significantly abnormal liver blood tests should not usually take it.
  • Caution is needed where muscle weakness could affect breathing or swallowing, or in significant heart or lung disease.
  • Use in pregnancy or breastfeeding should be discussed carefully with the specialist team.

Monitoring

  • Liver function blood tests before treatment and regularly during it.
  • Review of whether spasticity is improving, balanced against weakness and side effects.
  • Watching for signs of liver harm such as jaundice, dark urine or persistent nausea.

Side effects

  • Drowsiness, dizziness, tiredness and muscle weakness are common, especially at first.
  • Diarrhoea, nausea or loss of appetite can occur.
  • Less commonly, liver problems — report yellowing of the skin or eyes, dark urine or persistent sickness urgently.

Key interactions

  • Alcohol and other sedating medicines can add to drowsiness, so use with care.
  • Other medicines that can affect the liver may increase the risk to the liver.
  • Tell your team about all medicines, as some combinations need extra monitoring.

Available as: Capsules taken by mouth; an injectable form used in hospital for emergencies.

Answers

Dantrolene: frequently asked questions

Why do I need liver blood tests?

Dantrolene can occasionally harm the liver, so liver function is checked before and during treatment, and it is stopped if problems appear.

What should make me seek urgent advice?

Yellowing of the skin or eyes, dark urine, persistent nausea or unusual tiredness can signal liver trouble and should be reported promptly.

Will it make me drowsy or weak?

Drowsiness and muscle weakness are common, especially when starting, so take care with driving and tasks needing alertness.

Can I stop it if it is not helping?

Do not stop suddenly on your own; your team will review whether it is working and reduce or stop it appropriately.

What is malignant hyperthermia?

It is a rare, dangerous reaction to certain anaesthetics; dantrolene is the emergency hospital treatment used to control it.

The wider class

About Muscle relaxants

Dantrolene belongs to the muscle relaxants class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.

Skeletal muscle relaxantsReduce muscle spasticity and spasm in conditions such as MS and spinal injury. BaclofenA muscle relaxant that eases muscle stiffness and spasms in conditions such as multiple sc…TizanidineA muscle relaxant that eases muscle stiffness and spasm (spasticity), often used in multip…MethocarbamolA muscle relaxant used for short-term relief of painful muscle spasm, usually alongside re…OrphenadrineA muscle relaxant used for painful muscle spasm, with antimuscarinic (drying) effects.…CyclobenzaprineA muscle relaxant used for short-term relief of muscle spasm, which causes marked drowsine…CarisoprodolA muscle relaxant taken by mouth for short-term relief of painful muscle conditions, with …ChlorzoxazoneA muscle relaxant taken by mouth for short-term relief of painful muscle spasm, with a rar…MetaxaloneA muscle relaxant used for the short-term relief of muscle spasm, alongside rest and physi…SuccinylcholineA fast, short-acting muscle relaxant used during anaesthesia to paralyse muscles for placi…

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Authoritative sources

  • BNF
  • NICE CKS

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