Flu Diagnosis and Treatment »

Treatment for the Flu

Antiviral drugs are the most effective option for treating influenza. Four antiviral drugs (amantadine, rimantadine, zanamavir and oseltamivir) have been approved for treatment of the flu. All of these must be prescribed by a doctor. Antiviral treatment lasts for 5 days and must be started within the first 2 days of illness. However, you will need to begin taking an antiviral drug within 2 days after becoming sick. When used in this manner, these drugs can reduce influenza symptoms and may shorten the time you are sick by 1 or 2 days. The drugs also may make you less contagious.

Amantadine - This compound inhibit the growth of influenza viruses in cell culture and in experimental animals. Amantadine is only effective against influenza A, and some naturally occurring strains of influenza A are resistant to it. The mechanism of action of amantadine is not known. It is thought to act at the level of virus uncoating. The compound has been shown to have both therapeutic and prophylactic effects. Amantidine significantly reduces the duration of fever (51 hours as opposed to 74 hours) and illness. The compound also confers 70% protection against influenza A when given prophylactically. Amantidine can occasionally induce mild neurological symptoms such as insomnia, loss of concentration and mental disorientation. However, these symptoms quickly develops in susceptible individuals and cease when treatment is stopped. The therapeutic and prophylactic activity of amantadine is now generally accepted and numerous analogues of this compound have been prepared in place of amantadine for prophylaxis and the treatment of uncomplicated influenza A infections.

Rimantidine - Rimantadine is similar to amantidine but has fewer side effects. It is approved by the FDA for the treatment and prophylaxis of influenza A infection in persons one year or older. It should be used for uncomplicated influenza A infections only since it is thought to be less effective than amantidine. Amantadine and rimantadine resistant viruses are readily generated in the laboratory. Resistance has been linked to changes in the M2 protein. To date, the emergence of resistant influenza A has been documented primarily in young children undergoing therapy with rimantadine. The resistant viruses had been transmitted and caused influenza. The universal susceptibility of all types of naturally occurring influenza A isolated from man and animals suggests that resistance will be found only in individuals treated with the drug. The reason for the natural selection of the susceptible phenotype of influenza A in nature is not known.

Zanamivir - The rational approach to drug design has led to the design of several potent inhibitors of influenza neuraminidase. Zanamivir was the first neuraminidase inhibitor available for clinical use and is effective against both influenza A and B. Because of its poor bioavailability, zanamivir must be administered by inhalation. Zanamivir had been shown to be effective and devoid of significant side effects in clinical trials. It is now approved by the FDA for use as treatment for influenza A and B in persons 12 years or older but not for prophylaxis.

Oseltamivir - Oseltamivir is another neuraminidase inhibitor but unlike zanamivir, it can be given orally. Like zanamivir, it had been shown to be effective and devoid of significant side effects in clinical trials. It is approved by the FDA for use as treatment for influenza A and B in persons 18 years or older. It is also approved for prophylaxis in persons 13 years or older. Its lack of side effects would make particularly attractive in a family setting although its higher cost compared to amantidine and rimantidine should be taken into account.

All of the antiviral drugs may be effective for influenza A viruses. However, only oseltamivir and zanamivir are effective for influenza B viruses.

All of the antiviral drugs are different in terms of who can take them, how they are given, any dosing changes based on age or medical conditions, and side effects.