Dantrolene is a muscle relaxer that is used to treat muscle spasticity (stiffness and spasms) caused by conditions such as a spinal cord injury, stroke, cerebral palsy, or multiple sclerosis.

Dantrolene is also used to treat or prevent muscle stiffness and spasms caused by malignant hyperthermia (a rapid rise in body temperature and severe muscle contractions) that can occur during surgery with certain types of anesthesia.

Dantrolene may also be used for purposes not listed in this medication guide.

You should not take dantrolene if you have active liver disease. Do not take dantrolene at a time when you need muscle tone for safe balance and movement during certain activities.

Dantrolene can cause life-threatening liver damage, especially if you take high doses. Do not take dantrolene in larger amounts or for longer than recommended.

Call your doctor right away if you have signs of liver problems such as nausea, upper stomach pain, loss of appetite, dark urine, clay-colored stools, or jaundice (yellowing of the skin or eyes).

Dantrolene comes as a capsule to take by mouth. When used to treat spasticity, it is usually taken once a day for 7 days and then increased gradually every 7 days to three to four times a day. When used to prevent malignant hyperthermia, it is usually given three to four times a day, starting 1 or 2 days before surgery. When used after a malignant hyperthermia crisis, it is usually given in 4 divided doses for 1 to 3 days . Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take dantrolene exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Your doctor will probably start you on a low dose of dantrolene for spasticity and gradually increase your dose, not more than once every 7 days. If your symptoms do not improve or get worse within 45 days of taking dantrolene, call your doctor.

Your doctor will perform blood tests to make sure you do not have conditions that would prevent you from safely using dantrolene.

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.

Dantrolene can cause life-threatening liver damage, especially if you take high doses or take the medicine long-term. Use the medicine exactly as directed.

If you take dantrolene within 3 or 4 hours before surgery, use only enough water needed to swallow the capsule. Tell your doctor if you have trouble swallowing dantrolene.

You may need frequent blood tests to check your liver function.

Call your doctor if your muscle symptoms do not improve, or if they get worse.

If you need surgery, tell the surgeon ahead of time that you are using dantrolene.

Store at room temperature away from moisture, heat, and light. Keep the bottle tightly closed when not in use.

You should not use dantrolene if you are allergic to it, or if you have:

• active liver disease such as hepatitis or cirrhosis.

Do not take dantrolene at a time when you need muscle tone for safe balance and movement during certain activities. In some situations, it may be dangerous for you to have reduced muscle tone.

You may be more likely to develop liver problems while using dantrolene if you are a woman, if you are older than 35, or if you also take other medications. Ask your doctor about your individual risk.

Tell your doctor if you have ever had:

• liver disease;

• heart disease or a heart attack; or

• a breathing disorder such as COPD (chronic obstructive pulmonary disease).

It is not known whether this medicine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

Do not breastfeed while using this medicine, and for at least 3 days after your last dose.

Dantrolene should not be given to a child younger than 5 years old.

Use the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not use two doses at one time.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include severe muscle weakness, vomiting, diarrhea, or fainting.

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

Avoid driving or hazardous activity until you know how dantrolene will affect you. Dizziness or drowsiness can cause falls, accidents, or severe injuries.

Avoid exposure to sunlight or tanning beds. Dantrolene can make you sunburn more easily. Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors.

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor right away if you have signs of liver problems--nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, or jaundice (yellowing of the skin or eyes). These side effects may be most likely to occur between 3 and 12 months of your treatment with dantrolene.

Also call your doctor right away if you have:

• severe drowsiness;

• severe muscle weakness;

• weak or shallow breathing;

• severe or ongoing vomiting or diarrhea;

• problems with vision or speech;

• painful or difficult urination;

• a seizure; or

• a light-headed feeling, like you might pass out.

Common side effects of dantrolene may include:

• dizziness, drowsiness;

• diarrhea;

• weakness; or

• feeling tired.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Using dantrolene with other drugs that make you sleepy or slow your breathing can cause dangerous side effects or death. Ask your doctor before using opioid medication, a sleeping pill, a muscle relaxer, or medicine for anxiety or seizures.

Tell your doctor about all your other medicines, especially:

• heart or blood pressure medication;

• hormone replacement therapy; or

• hormonal birth control (pills, injections, implants, skin patches, or vaginal rings).

This list is not complete. Other drugs may affect dantrolene, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.