Flu-fighting drugs - Who should take them?

From Mayo Health Oasis

If you're ill with type A influenza (a respiratory infection that's different from a bad cold or upset stomach), it may be worth the effort to visit your doctor — especially if you're at risk for flu complications. Read on to see whether you're in a high-risk group. Two oral antiviral medications, amantadine (a-MAN-ta-deen) and rimantadine (rah-MAN-ta-deen), can prevent influenza A infection as well as reduce the duration and severity of the infection in progress. In addition, these drugs may provide added protection in conjunction with a flu shot.

If you haven't heard of these drugs before, it may be because they're only prescribed in specific situations. Amantadine (Symmetrel, Symadine) and rimantadine (Flumadine) are effective only against influenza type A infections, not influenza type B infections. Also, these drugs can only reduce the severity and shorten the duration of influenza A if they're administered within 48 hours of onset of illness. Most people with the flu wait too long before seeing a doctor for these drugs to be useful. And, if these drugs aren't taken appropriately in the course of an influenza infection, there is a risk that drug-resistance influenza may develop.

"That's why most people with the flu who are not at risk for complications are prescribed nothing more than bed rest and to drink plenty of fluids," explains Janet L. Vittone, M.D., a specialist in geriatric medicine at Mayo Clinic, Rochester, Minn. "By the time most otherwise healthy adults and children see a doctor, the flu has already run most of its course, and it's too late for an antiviral to be prescribed."

But influenza, which is marked by sudden high fever, sore throat, muscle aches and typically a dry, unproductive cough, is a serious illness that should be treated — particularly if you're 65 or older or have any medical condition that makes you more susceptible to respiratory complications. Influenza and complications such as pneumonia result in approximately 20,000 deaths in the United States each year.

The Centers for Disease Control and Prevention (CDC) report that U.S. influenza and pneumonia deaths were higher than anticipated during the first week of January 1998. That means that this year's flu season could be a particularly bad one.

Flu vaccine protects against most strains of influenza — but not all. This year, an unanticipated strain of influenza A known as the A/Sydney strain, has resulted in influenza outbreaks in several states. In addition, the flu vaccine takes 2 weeks to provide full protection, so if you're exposed to the flu shortly after you've been vaccinated, you may not be protected.

During an outbreak of influenza A, the CDC recommends preventive use of amantadine or rimantadine for people at high risk for flu-related complications (whether or not they received flu vaccine). Those at risk include people who have chronic medical conditions, such as chronic obstructive lung disease, cardiovascular disease and diabetes mellitus, particularly if they are elderly, and anyone with compromised immunity (such as someone taking the drug prednisone). Because influenza is extremely contagious and is transmitted (usually through the air) from person to person, people in crowded environments, such as residents of nursing homes, are at high risk of exposure and should be considered candidates for preventive use of antiviral drugs. Health care workers and anyone else who has contact with people in high risk groups could be considered for preventive doses as well.

These drugs are 70 percent to 90 percent effective in preventing influenza A infections. But again, they're not for widespread use. "If there is a known outbreak of influenza in a nursing home setting, physicians may prescribe these antivirals to residents to prevent the spread of influenza," says Dr. Vittone. "It's unlikely, however, that rimantadine and amantadine would be prescribed to everyone in a community or school where there is an outbreak of the flu."

Amantadine and rimatadine are therapeutically identical in terms of preventing influenza A. However, the incidence of side effects, especially in older people, is higher with amantadine. Amantadine has been on the market longer and costs significantly less than rimatadine.

Amantadine and rimantadine are approved for preventive use (but not as treatment for the flu) in children at risk for flu-related complications. These drugs are not recommended for people with seizure disorders.