Antivirals cope with influenza

May 1, 2005

Viral illnesses are notoriously difficult to treat. There are a host of antibiotics to fight bacteria, but until recently, most viruses were treated with over-the-counter analgesics plus supportive measures such as bed rest and fluids.

Four antiviral drugs have been approved for treatment of the flu:

Relenza and Tamiflu are neuraminidase inhibitors. When started promptly, they can decrease the severity and duration of both influenza A and B. Tamiflu is an oral medication, while Relenza is inhaled orally. Both appear to be effective in preventing influenza, although Relenza has not been officially approved by the FDA for this use. In animal studies, both appear to be effective against some strains of avian flu.

These medications shorten the disease process in otherwise healthy people. "What we'd really like to know, and what nobody does know, is the effect of drugs for influenza in people who are seriously ill," says Mark Abramowicz, MD, editor of The Medical Letter on Drugs and Therapeutics, a non-profit newsletter that critically appraises drugs. "We don't know whether that little bit of boost they give people who are experiencing a normal bout of flu would be lifesaving in the few people in whom the disease is out of control."

Flu vaccine is the main line of defense against influenza, since it offers protection that lasts for several months. Antiviral medications tend to be used for prevention in special situations, such as group living situations, or for immunodeficient patients who may respond poorly to the vaccine. "When a flu outbreak occurs in a nursing home you rush to vaccinate everybody, but the vaccine won't give them protective antibody levels for two weeks," explains Dr. Abramowicz. "In that situation you'd put everyone on amantadine or rimantadine in the meantime, to protect them until the vaccine takes effect."

This year, due to the vaccine shortage, some observers expected to see increased use of Relenza and Tamiflu, but in fact that didn't happen, says Daniel Winn, MD, senior medical director for CareFirst BlueCross BlueShield. "Of the two neuraminidase inhibitors, Relenza is more difficult to use, because it is inhaled, and can lead to coughing and bronchospasm," he says. "We haven't seen that much use of Tamiflu this flu season, either."