Examples

How It Works

These 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

These 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.

For the past few years, the U.S. Centers for Disease Control and Prevention (CDC) have advised doctors not to use amantadine (Symmetrel) or rimantadine (Flumadine) to treat or prevent the flu. These medicines have not worked against most types of the flu virus. Talk to your doctor about the medicine that is best to use for the current type of flu.

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

How Well It Works

Amantadine and rimantadine can relieve or prevent symptoms of influenza A if taken soon after infection. But these antiviral medicines do not always treat or prevent the flu.²

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

Side effects have been reported with both amantadine and rimantadine:¹

• Amantadine can cause sleeplessness (insomnia), hallucinations, and agitation in a small number of people (2%).
• Rimantadine often causes side effects that affect the digestive system, such as an upset stomach, nausea, and loss of appetite.

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 medication.

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 and rimantadine are 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.

Amantadine is removed from the body by the kidneys; rimantadine by the liver. This difference may have an impact on which medicine is used to treat people who have diseases affecting the kidneys or liver. Because side effects occur less often with rimantadine, it may be a better choice. But rimantadine costs more than amantadine.

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.
• Rimantadine is used to prevent and treat type A influenza in adults. But in children it is used only to prevent influenza A.

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

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