The Old Antivirals

Two drugs, amantadine (Symmetrel) and rimantadine (Flumadine), have been around for a while. They are approved for use as preventives and treatments, but they are effective only against Type A flu. If you cannot get the vaccine in time and you face a high risk of serious complications, these drugs can help protect you. They can also help people who have been immunized but who need extra protection, like an elderly person with heart or lung disease. Used as a preventive, the drugs would have to be taken daily for the entire flu season. Although a five-day course of amantadine costs only $3.50 and a similar course of rimantadine costs $8.75 (based on wholesale prices), taking them for four months or so can cost from $100 to more than $600. As treatment, a seven-day course would cost about $6 to $37, but at best the drugs shorten the illness by only one or two days. Both drugs can sometimes cause unpleasant -- and in rare cases, serious -- side effects, and the flu virus can become resistant to them. Amantadine's possible adverse effects, which abate with time, include nausea, vomiting, dizziness, insomnia, anxiety, impaired concentration and seizures. It can also cause adverse interactions with other drugs, like antihistamines and nervous system stimulants. Rimantadine is less likely to interact with other drugs, but it can cause similar adverse effects.

Two New Antivirals

Zanamivir (Relenza) and oseltamivir (Tamiflu) are now approved only as treatments, not preventives, and used as such they can cost up to 15 times as much as amantadine. But unlike amantadine, they work against Type A and Type B influenza viruses and for most people they are associated with fewer adverse effects. Also, there is no evidence that the flu virus can become resistant to them and there are no known interactions with other drugs. Zanamivir, a powder that is inhaled, is used twice a day for five days at a cost of about $44. Possible side effects include nasal and throat discomfort, cough and headache. People with breathing disorders like asthma can develop bronchial spasms and should always have a fast-acting bronchial dilators on hand when using this drug. Although zanamivir is not yet approved for preventing flu, a study at the University of Virginia and the University of Michigan, published last week in The New England Journal of Medicine, showed that when flu victims' family members were given zanamivir once a day for 10 days, their flu risk dropped by 79 percent. For the flu victim, taking the drug twice a day for five days shortened the duration of symptoms by two and a half days. Like zanamivir, oseltamivir, taken twice a day for five days, can reduce symptoms and shorten the flu duration by a day or more. Its most common adverse effects are nausea, vomiting and headache. At about $53 for a five-day supply, it is the most expensive flu treatment. In an experiment at the University of Virginia medical school in which healthy people were given infectious doses of flu virus, oseltamivir reduced the risk of infection by 61 percent and prevented the spread of flu virus in all cases. Both zanamivir and oseltamivir are intended for patients with uncomplicated cases of flu. But during the last flu season, there was serious concern about the misuse of these drugs in patients who had developed serious and in some cases fatal complications of the flu that should have been treated with antibiotics.