Amantadine for influenza (flu)

Examples

Generic Name	Brand Name
amantadine hydrochloride	Endantadine, Symmetrel

How It Works

Antiviral medicines prevent the spread of type A influenza by interfering with the production of the virus inside the body. They do not treat or protect you against influenza B.

Why It Is Used

Antiviral medicines reduce the severity of influenza (flu) symptoms and shorten the course of the illness of influenza A.¹ They need to be started within 48 hours of the first symptoms and continued, usually, for 7 days.

Canada's National Advisory Committee on Immunization (NACI) recommends using antiviral medicine to:²

• Control influenza A outbreaks in institutions such as nursing homes where people have a high risk of complications.
• Protect people who have a high risk of other problems and who have gotten a flu shot after an outbreak has started. It usually takes about 2 weeks (in children, up to 6 weeks) after getting a flu shot for the shot to start protecting you from getting the flu. These medicines can help protect you from getting the flu during that time.
• Protect people who did not get a flu shot and have live with or take care of people have a high risk of other problems. This includes family members, nursing home visitor, and healthcare workers.
• Protect people who have a disease that causes an impaired immune systems, such as cancer or diabetes.
• Protect people who cannot take the flu vaccine (for example, people who are allergic to eggs).

The NACI does not always recommend using these antiviral medicines to treat or prevent the flu because they do not work against all flu strains. Talk to your doctor about whether you should use an antiviral medicine for the current type of flu.

When used to protect people during a flu outbreak, antiviral medicines usually are taken for 7 days but may be needed for 5 to 7 weeks.

How Well It Works

In healthy young adults and children, antiviral medicines are 70% to 90% effective in preventing influenza A during an outbreak.³ However, these antiviral medicines do not always treat or prevent the flu.⁴

When given within 48 hours after symptoms begin, they may reduce symptoms, shorten the length of influenza A illness by 1 or 2 days, and allow for a faster return to usual activities.

Side Effects

In one study, approximately 13% of healthy adults taking amantadine had minor side effects, such as:³

• Sleeplessness (insomnia), dizziness, headache, nervousness, or an inability to concentrate. They are more common in people who are also taking antihistamines.
• Nausea, vomiting, loss of appetite (1% to 3%).

More serious but less frequent side effects (seizures, confusion) have been reported in older adults and, most commonly, in adults who have seizure disorders. Lowering the dose reduces these side effects without reducing the effectiveness of the medicine.

Side effects decrease after about 1 week of use and reverse as soon as treatment stops.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Amantadine is effective only against some type A influenza viruses.

Amantadine usually should not be taken at the same time as antihistamines or other medicines that stimulate the central nervous system. These may increase the risk of side effects such as insomnia, anxiety and, at high doses, seizures.

Little information exists regarding the effectiveness of antiviral medicines in treating children who have influenza A.

Amantadine is used to prevent and treat type A influenza in adults and in children older than age 1. It may prevent complications of type A influenza illness in high-risk people; the evidence is not conclusive.⁵

Amantadine may need to be given only once a day in older adults.

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Author:	Sydney Youngerman-Cole, RN, BSN, RNC	Last Updated: September 22, 2006
Medical Review:	Adam Husney, MD - Family Medicine W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
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