How does this medication work? What will it do for me?

Dantrolene belongs to a group of medications known as muscle relaxants. Dantrolene capsules are used to treat people with chronic muscle spasms caused by conditions such as cerebral palsy, multiple sclerosis, stroke, or spinal cord injury. Dantrolene helps these symptoms by preventing contractions or spasms of the muscles.

Dantrolene may also be used before surgery for people at risk of malignant hyperthermia and for follow-up treatment of this condition. Malignant hyperthermia is a syndrome of muscle rigidity and greatly increased body temperature that can be caused by a reaction to certain anesthetics. If left untreated, malignant hyperthermia can lead to death. The injectable form of dantrolene is used to treat someone who is experiencing malignant hyperthermia.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. If you have not discussed this with your doctor or are not sure why you are being given this medication, speak to your doctor. Do not stop using this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to use this medication if their doctor has not prescribed it.

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What form(s) does this medication come in?

Capsules

25 mg
Each opaque orange and brown capsule (opaque orange cap and opaque light tan to brown body), coded with 1 black bar and "DANTRIUM 25 mg 0149 0030", contains dantrolene sodium 25 mg. Nonmedicinal ingredients: edible black ink, gelatin, iron oxide red, iron oxide yellow, lactose, magnesium stearate, starch, talc, and titanium dioxide.

100 mg
Each opaque orange and brown capsule (opaque orange cap and opaque light tan to brown body), coded with 3 black bars and "DANTRIUM 100 mg 0149 0033", contains dantrolene sodium 100 mg. Nonmedicinal ingredients: edible black ink, gelatin, iron oxide red, iron oxide yellow, lactose, magnesium stearate, starch, talc, and titanium dioxide.

Intravenous

Each vial contains a sterile lyophilized mixture of 20 mg dantrolene sodium, 3,000 mg mannitol, and sufficient sodium hydroxide to yield a pH of approximately 9.5 when reconstituted.

How should I use this medication?

The usual starting dose for adults is 25 mg once daily. The dose is then increased gradually until the best dose is found, based on individual response and needs. The best dose is the lowest dose that will control muscle spasms. Most people respond to doses of 400 mg daily (given in divided doses, usually as 100 mg 4 times daily) or less.

Children's dosing is based on body weight. Children should not be given doses higher than 100 mg 4 times daily.

The injectable form of dantrolene is dosed based on body weight.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are using the medication without consulting your doctor.

It is important to use this medication exactly as prescribed by your doctor. If you miss a dose, administer it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not administer a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

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Who should NOT take this medication?

Dantrolene should not be used by anyone who:

  • is allergic to dantrolene or to any of the ingredients of the medication
  • has a particular type of muscle spasm (one that, in the doctor's opinion, may actually help increase or maintain the person's ability to function)
  • has active liver disease (such as hepatitis or cirrhosis)
  • has poor lung function (such as obstructive pulmonary disease)
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What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent. The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • abdominal or stomach cramps or discomfort
  • chills and fever
  • diarrhea
  • difficulty swallowing
  • dizziness
  • drowsiness
  • frequent urge to urinate or uncontrolled urination
  • general feeling of discomfort or illness
  • headache
  • loss of appetite
  • muscle weakness
  • nausea or vomiting
  • skin rash
  • unusual tiredness

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • confusion
  • constipation
  • depression
  • symptoms of liver damage (e.g., yellow skin or eyes, abdominal pain, dark urine, clay-coloured stools, loss of appetite)

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • chest pain
  • convulsions (seizures)
  • pain, tenderness, changes in skin colour, or swelling of foot or leg
  • shortness of breath or slow or troubled breathing

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Cancer: Dantrolene has been shown to cause cancer in rats. The potential for dantrolene to cause cancer in humans cannot be ruled out. If you have any questions or concerns, talk to your doctor.

Drowsiness/reduced alertness: This medication may temporarily cause drowsiness, which may impair your ability to drive or operate machinery. These effects should only last about a week. Avoid hazardous tasks for the first week of treatment.

Heart function: While taking this medication, people with heart disease should be closely monitored by their doctors.

Liver injury: Dantrolene capsules may be toxic to the liver, or worsen existing liver damage. The risk of liver injury is greater for women, people over 30 years of age, people taking other medications, and people taking other therapies that may cause liver damage. If you have liver disease, talk to your doctor about whether you should use this medication. People using this medication will likely have liver tests before and during use.

Lung function: While taking this medication, people with impaired lung function should be closely monitored by their doctors.

Muscle weakness: Some people taking dantrolene feel excessively weak as long as they are taking the medication. These people may not be able to use rehabilitation devices such as crutches, wheelchairs, braces, walkers, or canes. If you use any of these devices and experience persistent weakness that interferes with the use of these devices, you should talk to your doctor. You may have to stop taking this medication.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. This medication should not be used by women who are breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children under 5 years of age.

What other drugs could interact with this medication?

There may be an interaction between dantrolene and any of the following:

  • alcohol or other medications that cause drowsiness (e.g., tranquilizers)
  • calcium channel blockers (e.g., amlodipine, diltiazem, verapamil)
  • droperidol
  • methotrimperazine

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.