Flu Medications

Information, Articles, Resources

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.

Some medications can be used to decrease the severity and duration of a flu attack. Four prescription antiviral medications for influenza are available in the United States:

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

All four drugs are available by prescription only.

This four drugs are classified into two classes, the adamantane derivatives and the neuraminidase inhibitors, on the basis of their chemical properties and activities against influenza viruses. Controlled clinical trials have demonstrated the efficacy of all four antiviral medications in reducing symptom duration when used for treatment of influenza infections. Three of the antiviral drugs have been approved for use as chemoprophylaxis.

Relenza (zanamivir) and Tamiflu (oseltamivir) differ from Symmetrel (amantadine) and Flumadine (rimantadine) in terms of their side effects and cost. Use of Symmetrel (amantadine) and rimantadine (Flumadine), 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). On the other hand, Tamiflu (oseltamivir) and Relenza (zanamivir) are significantly more expensive than either Flumadine (rimantadine) or Symmetrel (amantadine).

Amantadine (Symmetrel), rimantadine (Flumadine), and oseltamivir (Tamiflu) are administered orally. Amantadine (Symmetrel) and rimantadine (Flumadine) are available in tablet or syrup form, and oseltamivir (Tamiflu) is available in capsule or oral suspension form. Zanamivir (Relenza) is available as a dry powder that is self-administered via oral inhalation by using a plastic device included in the package with the medication.

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 (Tamiflu) and Zanamivir (Relenza) 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.

This antiviral medications were approved in 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 chemoprophylaxis of influenza. Relenza is not approved for chemoprophylaxis of influenza.

Adamantane Derivatives

The adamantane derivatives, amantadine (Symmetrel) and rimantadine (Flumadine), are chemically related, orally administered drugs that are approved for treatment and chemoprophylaxis of influenza A. Amantadine (Symmetrel) and rimantadine (Flumadine) 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 administered 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 chemoprophylaxis, amantadine (Symmetrel) and rimantadine (Flumadine) are approximately 70% - 90% effective in preventing symptoms of influenza A illness.

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.