Flu Medications

The flu (Influenza) is an infection of the respiratory tract caused by the influenza virus. High fever, body aches, extreme tiredness, and dry cough are symptoms of the flu.

Antiviral medications can be used to decrease the severity and duration of a flu attack. Currently, four prescription antiviral medications are approved by the US FDA for the treatment and prevention of flu:

• amantadine (Symmetrel)
• rimantadine (Flumadine)
• oseltamivir (Tamiflu)
• zanamivir (Relenza)

All four antiviral drugs are available by prescription only.

Anti-influenza medications are classified into two classes, the adamantane derivatives and the neuraminidase inhibitors, on the basis of their chemical properties and activities against flu viruses.

Antiviral drugs differs in terms of approved uses, approved ages, how they are taken, side effects and costs.

Neuraminidase Inhibitors

The neuraminidase inhibitors, oseltamivir (Tamiflu) and Zanamivir (Relenza), are chemically related drugs that have activity against both influenza A and influenza B viruses. Oseltamivir and Zanamivir block the active site of the influenza viral enzyme neuraminidase, which is common to both influenza A and influenza B viruses. This effect results in viral aggregation at the host cell surface and reduces the number of viruses released from the infected cell.

The neuraminidase inhibitors are on the market since 1999. When used within 48 hours of illness onset, both drugs decrease shedding and reduce the duration of influenza symptoms by approximately 1 day. The recommended duration of treatment with either oseltamivir (Tamiflu) and Zanamivir (Relenza) is 5 days. Tamiflu is also approved for prophylaxis of influenza.

Tamiflu is available as tablets and liquid suspension for children. Zanamivir is available as inhalation and can be inhaled using a device known as a Diskhaler.

Tamifluand Relenza are significantly more expensive than either Flumadine (rimantadine) or Symmetrel (amantadine).

Adamantane Derivatives

The adamantane derivatives, amantadine (Symmetrel) and rimantadine (Flumadine), are chemically related, oral drugs approved for treatment and chemoprophylaxis of influenza A. Amantadine and rimantadine specifically inhibit replication of influenza A viruses, but not influenza B viruses. This drugs are thought to interfere with influenza A virus M2 protein, a membrane ion channel protein, and inhibit virus uncoating, which inhibits virus replication, resulting in decreased viral shedding.

Amantadine (Symmetrel) is approved for the treatment of influenza A in children aged 1 year and older and in adults. Rimantadine (Flumadine) is approved for treatment of influenza A in adults. Both drugs are approved for chemoprophylaxis to prevent influenza A in people aged 1 year and older. When taken within 48 hours of illness onset, both medications decrease viral shedding and reduce influenza A illness by approximately 1 day. The usual recommended duration of treatment is 5 days. When used for flu prevention amantadine (Symmetrel) and rimantadine (Flumadine) are approximately 70% - 90% effective in preventing symptoms of influenza A.

Use of amantadine and rimantadine has been associated with central nervous system side effects such as nervousness, anxiety, insomnia, and lightheadedness. These side effects have not been associated with Tamiflu (oseltamivir) and Relenza (zanamivir).

Some of the antiviral drugs can be prescribed for children over one year of age. Consult your doctor as soon as possible after flu symptoms appear, or whenever a child has a fever.

The anti-influenza antiviral medications are not a substitute for vaccine and are used only as an adjunct to vaccine in the control of flu.

Complications of influenza, may require different treatment and may need urgent medical attention. Use of antiviral drugs does not eliminate the risk of complications, and some complications (as well as other medical conditions that could be confused with influenza) can be life threatening. Influenza viruses can become resistant to specific anti-influenza antiviral drugs, and all of the drugs have side effects. Therefore, if you have new symptoms during treatment, or your symptoms persist or get worse during treatment, you should see your health care professional.

Last Updated: January 2010