Amantadine belongs to the family of medications called antivirals. It is sometimes used to prevent and treat influenza A infections, although its use has become limited due to viral resistance. It is believed to work by preventing the virus from reproducing. If used to prevent an infection, amantadine must be taken before exposure to the flu virus.

Amantadine also belongs to the family of medications called antiparkinsonians. It is also used to treat Parkinson's disease and for the short-term management of Parkinson-like symptoms caused by certain medications. The way it works is not clear, but it appears to help Parkinson's disease by increasing the levels of a chemical called dopamine in the brain. Not having enough dopamine in the brain is believed to be a cause of the symptoms of Parkinson's disease. Amantadine generally begins to work within 2 days.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking 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 take this medication if their doctor has not prescribed it.

The recommended adult dose of amantadine varies according to the condition being treated.

For treatment of Parkinson's disease, the recommended adult dose is 100 mg once daily to start. After 1 to 2 weeks, your doctor may recommend increasing the dose to 100 mg twice daily. The maximum daily dose is 400 mg in divided doses.

For treatment and prevention of influenza A infections, the recommended dose for adults and children 10 years of age and older is 200 mg daily in 1 dose or in 2 divided doses.

For children who are under 10 years of age, the dosage is based on body weight. The recommended dose of amantadine is 4.5 mg to 9.0 mg per kilogram of body weight. The maximum dose for children 9 years and over is 200 mg daily. Children under 9 years of age should not be given more than 150 mg daily.

The appropriate dose is taken 2 or 3 times a day, as determined by your doctor.

• To prevent influenza A infections, amantadine should be taken before or after contact with a person infected with influenza A, and continued for at least 10 days after contact with the virus.
• To treat influenza A infections, amantadine should be taken within 24 to 48 hours of the start of flu symptoms, and continued for 24 to 48 hours after the symptoms disappear.

Many things can affect the dose of 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 taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take 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 take 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 in a dry place and keep it out of the reach of children.

Do not use this medication if you are allergic to amantadine or any ingredients of the 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.

• agitation
• anxiety and irritability
• constipation
• diarrhea
• dizziness or lightheadedness
• drowsiness
• dry mouth
• dry nose
• headache
• loss of appetite
• muscle pain
• nausea
• nervousness
• nightmares or vivid dreams
• overexcitement
• purplish-red blotchy spots on skin
• sweating
• trouble sleeping
• vomiting

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

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

• confusion
• hallucinations (seeing or hearing things that are not there)
• problems urinating or loss of bladder control
• signs of depression, e.g.:
• changes in sleep
• changes in weight
• decreased interest in activities
• poor concentration
• thoughts of suicide
• signs of heart problems (e.g., swelling of the hands, feet, or lower legs, difficulty breathing)
• skin changes
• slurred speech
• trembling or uncontrolled muscle movements

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

• blurry vision
• seizures
• symptoms of a severe allergic reaction (e.g., swelling of the hands, feet, ankles, face, lips, mouth, or throat; difficulty breathing or swallowing)
• thoughts of suicide or attempts at suicide

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.

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.

Behaviour changes and suicidal thoughts: There have been reports of behaviour changes and thoughts of suicide or wanting to harm others in people who have taken amantadine. Some individuals have experienced abnormal behaviour such as compulsive gambling, compulsive shopping, hypersexuality, and binge eating. If you experience these symptoms or any other behaviour changes while taking this medication, contact your doctor immediately. Family members or caregivers of people who are taking this medication should contact your doctor immediately if they notice unusual behaviour changes.

Congestive heart failure: Amantadine can cause side effects that contribute to heart failure. If you have a history of congestive heart failure or fluid retention, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Dental problems: Amantadine may cause a decrease in saliva flow and increase the risk of cavities, periodontal disease, oral candidiasis (fungal infection), and discomfort. Your doctor, dentist, or pharmacist may be able to suggest ways to reduce these effects.

Drowsiness/reduced alertness: Amantadine may cause drowsiness or blurred vision. Do not drive, operate machinery, or perform other potentially hazardous tasks until you have determined how this medication affects you.

Effectiveness: The benefit of amantadine has not been seen for the treatment of flu symptoms that have been present for more than 2 days.

Flu shots: Amantadine is not a substitute for the flu shot. Continue to receive an annual flu shot as advised by your doctor.

Glaucoma: Amantadine can cause your pupils to dilate, affecting the severity of glaucoma. If you have angle closure glaucoma, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Kidney function: Decreased kidney function or kidney disease can cause this medication to build up in the body, causing side effects. If you have kidney disease or reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver disease: If you have a history of liver disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Mental conditions: If you have a mental health condition, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Neuroleptic malignant syndrome (NMS): Neuroleptic malignant syndrome has been reported in people who reduced or stopped taking amantadine. It is an uncommon but life-threatening syndrome characterized by fever, muscle stiffness, involuntary movements, altered consciousness, increased heart rate and breathing rate, and fluctuating blood pressure. If you experience any of these symptoms, seek immediate medical attention.

Parkinson's disease: People with Parkinson's disease whose condition improves with amantadine treatment should gradually and cautiously resume normal activities until they determine their ability to tolerate this medication. Do not suddenly stop taking amantadine for Parkinson's disease as this may cause a sudden worsening of your condition.

Rash: If you have a history of recurrent (eczematoid) rash, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Seizures: Amantadine may cause seizure if you are at risk of experiencing seizures. If you have a history of epilepsy or other seizures, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Pregnancy: This medication can cause birth defects if it is taken by pregnant women. Amantadine 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. If you are a breast-feeding mother and are taking amantadine, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding. Amantadine is not recommended for use by breast-feeding mothers.

Children: The safety and effectiveness of using this medication have not been established for newborns and infants under one year old.

Seniors: Seniors are more likely to experience side effects with normal adult doses of amantadine. As a result, they may require a lower dose of amantadine.

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

• aclidinium
• alcohol
• atropine
• amoxapine
• antihistamines (e.g., bilastine, dimenhydrinate, diphenhydramine, rupatadine)
• antipsychotics (e.g., clozapine, haloperidol, quetiapine, risperidone)
• benztropine
• bupropion
• carbonic anhydrase inhibitors (e.g., acetazolamide, brinzolamide, dorzolamide, topiramate)
• cyclobenzaprine
• darifenacin
• disopyramide
• fesoterodine
• glycopyrrolate
• influenza vaccine
• ipratropium
• memantine
• metoclopramide
• moclobemide
• orphenadrine
• oxybutynin
• pizotifen
• scopolamine
• solifenacin
• solriamfetol
• sulfamethoxazole
• tiotropium
• tolterodine
• topiramate
• triamterene
• trimethoprim
• tricyclic antidepressants (e.g., amitriptyline, doxepin, nortriptyline)
• trospium
• umeclidinium

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.