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 Dantrium (Dantrolene). If you are concerned about side effects, discuss the risks and benefits of Dantrium (Dantrolene) with your doctor.

The following side effects have been reported by at least 1% of people taking Dantrium (Dantrolene). 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
• sweating
• 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
• signs of Depression (e.g., poor concentration, changes in weight, changes in sleep, decreased interest in activities, thoughts of suicide)
• symptoms of liver damage (e.g., yellow skin or eyes, abdominal pain, dark urine, clay-coloured stools, loss of appetite)
• worsening symptoms of heart failure (e.g., difficulty breathing, rapid weight gain, swollen ankles or feet)

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

• chest pain
• convulsions (seizures)
• fast or pounding heartbeat
• 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 Dantrium (Dantrolene).

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 25 mg of Dantrium (Dantrolene) sodium. 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 of Dantrium (Dantrolene) sodium, 3,000 mg of mannitol, and sufficient sodium hydroxide to yield a pH of approximately 9.5 when reconstituted.

Do not take Dantrium (Dantrolene) if you:

• are allergic to Dantrium (Dantrolene) or to any of the ingredients of the medication
• have a particular type of muscle spasm (one that, in the doctor's opinion, may actually help increase or maintain your ability to function)
• have active liver disease (such as hepatitis or cirrhosis)
• have poor lung function (such as obstructive pulmonary disease)

There may be an interaction between Dantrium (Dantrolene) and any of the following:

• alcohol
• antihistamines (e.g., cetirizine, doxylamine, Diphenhydramine, Hydroxyzine, Loratadine)
• antipsychotics (e.g., Chlorpromazine, Clozapine, Haloperidol, Olanzapine, Quetiapine, Risperidone)
• Apalutamide
• benzodiazepines (e.g., Alprazolam, Diazepam, Lorazepam)
• Bosentan
• brimonidine
• Buspirone
• calcium channel blockers (e.g., Amlodipine, Diltiazem, Verapamil)
• cannabis
• chloral hydrate
• Dabrafenib
• Deferasirox
• Dexamethasone
• efavirenz
• Enzalutamide
• estrogens (e.g., conjugated estrogen, Estradiol, ethinyl estradiol)
• etravirine
• Methadone
• Mirtazapine
• Mitotane
• Modafinil
• muscle relaxants (e.g., Baclofen, Cyclobenzaprine, methocarbamol, orphenadrine)
• Nabilone
• narcotic pain relievers (e.g., Codeine, Fentanyl, Morphine, Oxycodone)
• Pramipexole
• rifabutin
• rifampin
• Ropinirole
• Rotigotine
• St. John's wort
• scopolamine
• seizure medications (e.g., Carbamazepine, Clobazam, Levetiracetam, Phenobarbital, Phenytoin, primidone, Topiramate, Valproic acid, zonisamide)
• selective serotonin reuptake inhibitors (SSRIs; e.g., Citalopram, Fluoxetine, Paroxetine, Sertraline)
• siltuximab
• sodium oxybate
• Tapentadol
• thalidomide
• Tocilizumab
• Tramadol
• tricyclic antidepressants (e.g., Clomipramine, Desipramine, Imipramine)
• Zolpidem
• Zopiclone

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 Dantrium (Dantrolene). 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.

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 Dantrium (Dantrolene).

Cancer: The potential for Dantrium (Dantrolene) to cause cancer in humans cannot be ruled out. If you have any questions or concerns, talk to your doctor.

Drowsiness/reduced alertness: Dantrium (Dantrolene) 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: If you have heart disease, you should be monitored closely by your doctor while taking Dantrium (Dantrolene).

Liver injury: Dantrium (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 old, people taking other medications, and people taking other therapies that may cause liver damage. If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

If you have liver disease, talk to your doctor about whether you should use Dantrium (Dantrolene). People using Dantrium (Dantrolene) will likely have liver tests before and during use.

Lung function: If you have impaired lung function, you should be monitored closely by your doctor while taking Dantrium (Dantrolene)

Muscle weakness: Some people taking Dantrium (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 Dantrium (Dantrolene).

Pregnancy: Dantrium (Dantrolene) should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Dantrium (Dantrolene), contact your doctor immediately.

Breast-feeding: Dantrium (Dantrolene) passes into breast milk. If you are a breast-feeding mother and are taking Dantrium (Dantrolene), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using Dantrium (Dantrolene) have not been established for children under 5 years old.