In the U.S.—

In Canada—

• Antispastic
• Duchenne muscular dystrophy therapy adjunct
• Malignant hyperthermia therapy adjunct
• Muscle phosphorylase deficiency therapy adjunct
• Neuroleptic malignant syndrome therapy adjunct

Dantrolene (DAN-troe-leen ) is used to help relax certain muscles in your body. It relieves the spasms, cramping, and tightness of muscles caused by certain medical problems such as multiple sclerosis (MS), cerebral palsy, stroke, or injury to the spine. Dantrolene does not cure these problems, but it may allow other treatment, such as physical therapy, to be more helpful in improving your condition. Dantrolene acts directly on the muscles to produce its relaxant effects.

Dantrolene is also used to prevent or treat a medical problem called malignant hyperthermia that may occur in some people during or following surgery or anesthesia. Malignant hyperthermia consists of a group of symptoms including very high fever, fast and irregular heartbeat, and breathing problems. It is believed that the tendency to develop malignant hyperthermia is inherited.

Dantrolene has been shown to cause cancer and noncancerous tumors in some animals (but not in others) when given in large doses for a long time. It is not known whether long-term use of dantrolene causes cancer or tumors in humans. Before taking this medicine, be sure that you have discussed this with your doctor.

This medicine is available only with your doctor's prescription, in the following dosage forms:

Oral
• Capsules (U.S. and Canada)

Parenteral
• Injection (U.S. and Canada)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For dantrolene, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to dantrolene. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Dantrolene has not been shown to cause birth defects or other problems in humans.

Breast-feeding—Use of dantrolene is not recommended during breast-feeding.

Children—This medicine has been tested in children 5 years of age and older and has not been shown to cause different side effects or problems than it does in adults.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is no specific information comparing use of dantrolene in the elderly with use in other age groups.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking dantrolene, it is especially important that your health care professional know if you are taking any of the following:

• Acetaminophen (e.g., Tylenol) (with long-term, high-dose use) or
• Amiodarone (e.g., Cordarone) or
• Anabolic steroids (dromostanolone [e.g., Drolban], ethylestrenol [e.g., Maxibolin], nandrolone [e.g., Anabolin], oxandrolone [e.g., Anavar], oxymetholone [e.g., Anadrol], stanozolol [e.g., Winstrol]) or
• Androgens (male hormones) or
• Anti-infectives by mouth or by injection (medicine for infection) or
• Antithyroid agents (medicine for overactive thyroid) or
• Carbamazepine (e.g., Tegretol) or
• Carmustine (e.g., BiCNU) or
• Central nervous system (CNS) depressants (medicine that causes drowsiness) or
• Chloroquine (e.g., Aralen) or
• Daunorubicin (e.g., Cerubidine) or
• Disulfiram (e.g., Antabuse) or
• Divalproex (e.g., Depakote) or
• Estrogens (female hormones) or
• Etretinate (e.g., Tegison) or
• Gold salts (medicine for arthritis) or
• Hydroxychloroquine (e.g., Plaquenil) or
• Mercaptopurine (e.g., Purinethol) or
• Methotrexate (e.g., Mexate) or
• Methyldopa (e.g., Aldomet) or
• Naltrexone (e.g., Trexan) (with long-term, high-dose use) or
• Oral contraceptives (birth control pills) containing estrogen or
• Phenothiazines (acetophenazine [e.g., Tindal], chlorpromazine [e.g., Thorazine], fluphenazine [e.g., Prolixin], mesoridazine [e.g., Serentil], perphenazine [e.g., Trilafon], prochlorperazine [e.g., Compazine], promazine [e.g., Sparine], promethazine [e.g., Phenergan], thioridazine [e.g., Mellaril], trifluoperazine [e.g., Stelazine], triflupromazine [e.g., Vesprin], trimeprazine [e.g., Temaril]) or
• Phenytoin (e.g., Dilantin) or
• Plicamycin (e.g., Mithracin) or
• Tricyclic antidepressants (medicine for depression) (amitriptyline [e.g., Elavil], amoxapine [e.g., Asendin], clomipramine [e.g., Anafranil], desipramine [e.g., Pertofrane], doxepin [e.g., Sinequan], imipramine [e.g., Tofranil], nortriptyline [e.g., Aventyl], protriptyline [e.g., Vivactil], trimipramine [e.g., Surmontil]) or
• Valproic acid (e.g., Depakene)—The chance of side effects may be increased

• Emphysema, asthma, bronchitis, or other chronic lung disease or
• Heart disease or
• Liver disease, such as hepatitis or cirrhosis (or history of)—The chance of serious side effects may be increased

If you are unable to swallow the capsules, you may empty the number of capsules needed for one dose into a small amount of fruit juice or other liquid. Stir gently to mix the powder with the liquid before drinking. Drink the medicine right away. Rinse the glass with a little more liquid and drink that also to make sure that you have taken all of the medicine.

Dantrolene may be taken with or without food or on a full or empty stomach. However, if your doctor tells you to take the medicine a certain way, take it exactly as directed.

Take this medicine only as directed by your doctor . Do not take more of it and do not take it more often than your doctor ordered. Dantrolene may cause liver damage or other unwanted effects if too much is taken.

Dosing—

The dose of dantrolene will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of dantrolene. If your dose is different, do not change it unless your doctor tells you to do so:

The number of capsules that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking dantrolene.

• For oral dosage form (capsules):
  • For prevention or treatment of a malignant hyperthermic crisis:
    • Adults—Dose is based on body weight and must be determined by your doctor. The usual dose is 4 to 8 milligrams (mg) per kilogram (kg) (1.8 to 3.6 mg per pound) of body weight. The doctor will instruct you exactly when and how often to take your medicine.
  • To relieve spasms:
    • Adults—To start, 25 mg once a day. The doctor may increase your dose as needed and tolerated. However, the dose is usually not more than 100 mg four times a day.
    • Children—Dose is based on body weight and must be determined by your doctor. To start, the dose is usually 0.5 mg per kg (0.23 mg per pound) of body weight twice a day. The doctor may increase the dose as needed and tolerated. However, the dose is usually not more than 3 mg per kg or 100 mg four times a day.
• For injection dosage form:
  • For prevention or treatment of a malignant hyperthermia crisis:
    • Adults, teenagers, and children—Dose is based on body weight and must be determined by your doctor.

Missed dose—

If you miss a dose of this medicine and remember within an hour or so of the missed dose, take it right away. Then go back to your regular dosing schedule. But if you do not remember until later, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

If you will be taking dantrolene for a long time (for example, for several months at a time), your doctor should check your progress at regular visits. It may be necessary to have certain blood tests to check for unwanted effects while you are taking dantrolene.

This medicine will add to the effects of alcohol and other CNS depressants (medicines that slow down the nervous system, possibly causing drowsiness). Some examples of CNS depressants are antihistamines or medicine for hay fever, other allergies, or colds; sedatives, tranquilizers, or sleeping medicine; prescription pain medicine or narcotics; barbiturates; medicine for seizures; other muscle relaxants; or anesthetics, including some dental anesthetics. Therefore, do not drink alcoholic beverages, and check with your doctor before taking any of the medicines listed above, while you are using this medicine.

This medicine may cause drowsiness, dizziness or lightheadedness, vision problems, or muscle weakness in some people. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert, well-coordinated, and able to see well.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Serious side effects are very rare when dantrolene is taken for a short time (for example, when it is used for a few days before, during, or after surgery or anesthesia to prevent or treat malignant hyperthermia). However, serious side effects may occur, especially when the medicine is taken for a long time.

Check with your doctor immediately if any of the following side effects occur:

• Less common
  • Convulsions (seizures);  pain, tenderness, changes in skin color, or swelling of foot or leg;  shortness of breath or slow or troubled breathing 
  
  

Also, check with your doctor as soon as possible if any of the following side effects occur:

• Less common
  • Bloody or dark urine;  chest pain;  confusion;  constipation (severe);  diarrhea (severe);  difficult urination ;  mental depression;  skin rash, hives, or itching;  yellow eyes or skin 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• More common
  • Diarrhea (mild);  dizziness or lightheadedness ;  drowsiness;  general feeling of discomfort or illness;  muscle weakness;  nausea or vomiting;  unusual tiredness  
  
  

• Less common
  • Abdominal or stomach cramps or discomfort;  blurred or double vision or any change in vision;  chills and fever;  constipation (mild);  difficulty in swallowing;  frequent urge to urinate or uncontrolled urination;  headache;  loss of appetite;  slurring of speech or other speech problems;  sudden decrease in amount of urine;  trouble in sleeping;  unusual nervousness 
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.