By Richard Harkness
Enquirer contributor

Question: I understand there are pills you can take to prevent the flu. Can they be used instead of a flu shot?

Answer: There are four antiviral drugs that can help prevent the flu or shorten its duration after you get it. Three are in pill form and one is a powder for inhalation. Symmetrel and Flumadine are older agents, while Tamiflu and Relenza (the powder) are more recently approved agents.

However, it must be emphasized that these drugs are not a substitute for a flu vaccination. Think of the flu shot as first-line prevention and the drugs as second-line agents that can be used in certain situations during flu season.

Though the older drugs work about as well as the newer ones, they are effective only against Influenza A. The newer drugs, called neuraminidase inhibitors, work against both Influenza A and B.

Tamiflu is a capsule taken by mouth twice daily for five days. Relenza is a powder designed to be inhaled through the mouth similarly to some asthma medications - two inhalations twice daily for five days. Use of Relenza has been associated with breathing problems in some individuals, particularly those with lung diseases.

If used within two days of coming down with flu symptoms, antiviral drugs may shorten the duration of illness by a day or so. They work by disabling an enzyme on the surface of the influenza virus. Without the enzyme, the virus is powerless to attack other body cells and thus its replication is stalled.

Complementary role

The best use of these drugs may be in flu prevention. It takes about two weeks after getting a flu shot for your body to build up adequate defenses against flu viruses. Because of this lag time, antiviral drugs can play an important complementary role in preventing the flu in specific situations.

For instance, after a flu outbreak has begun, the drugs should be considered for use in unvaccinated or very recently vaccinated high-risk individuals, such as the elderly and those with chronic diseases. Similarly, during flu outbreaks in the community or in institutions (e.g., hospitals, nursing homes), unvaccinated caregivers could take the drugs to help prevent spread of the flu to the high-risk individuals they care for. The drugs should also be considered for those who are allergic to the flu shot. It's interesting to note that Flumadine was used to successfully control a flu outbreak aboard a cruise ship.

Flu or cold?

How do you tell whether you have the flu or a cold? Influenza is a specific illness that produces high fever and chills, sore throat, intense fatigue, severe muscle aches and headache. A cold is much less severe, typically causing a cough, mild sore throat, congestion and a low-grade fever. If you have the flu, you'll know it.

E-mail rharkn@aol.com.