Antivirals receive renewed attention this flu season 

CDC stockpiling drugs in case of shortages

With the flu vaccine supply cut almost in half this season, health care providers and officials are turning to antivirals to fill in the gap.

No one knows, however, if the four antiviral medications — amantadine (Symmetrel), rimantadine (Flumadine), zanamivir (Relenza), and oseltamivir (Tamiflu) — can meet the demand either. Robert B. Couch, MD, once tried to find out from distributors about the amount of antiviral supply. The professor of medicine and professor and chairman of microbiology and immunology at Baylor College of Medicine in Houston says the distributors wouldn’t send the information to him. "It is a concern that there is not enough drug out there for what people might wish to have."

Keri K. Hall, MD, assistant professor in the department of internal medicine, division of infectious diseases, at the University of Virginia in Charlottesville, knows about previous antiviral shortages in the past, but is not sure what this year will bring. "I am not aware of any specific reasons to be concerned about a shortage from a manufacturing side or anything like that."

The Centers for Disease Control and Prevention (CDC) in Atlanta has issued interim guidelines on the use of these antiviral medicines in the prevention and treatment of flu for this coming season. These guidelines are available at www.cdc.gov/flu/professionals/treatment/0405antiviralguide.htm. The CDC says the interim guidelines are provided, in conjunction with previously issued recommendations on use of vaccine, to reduce the impact of influenza on persons at high risk for developing severe complications secondary to infection.

The antiviral medications are approved for two different situations, Hall says. The first is for treatment of flu. The second is for prophylaxis, to prevent individuals from becoming infected with flu.

"Those individuals who we give prophylaxis to are the ones who are high risk to develop complications of the flu and they have a known exposure to someone with the flu," she explains.

The CDC encourages the use of amantadine or rimantadine for chemoprophylaxis and the use of oseltamivir or zanamivir for treatment as supplies allow, in part to minimize the development of adamantane resistance among circulating influenza viruses.

Amantadine, which is generically available, is licensed for prevention and for treatment in those older than age 1, Couch says. "None of the other three drugs cover all age groups."

The CDC recently updated its recommendations to include information on antiviral use in children. Rimantadine, for example, is approved for prophylaxis of influenza among children older than 1 year of age and for treatment and prophylaxis of influenza among adults. However, the CDC says that certain specialists in the management of influenza consider rimantadine appropriate for treatment of influenza among children.

"My pediatrician colleagues and all of us say rimantadine is perfectly all right [for use in children]," Couch says. "The information is available. It can be used and is used. It is just not approved by the FDA for that purpose."

Also available for treatment of children are amantadine (children older than 1 year of age), oseltamivir (children older than 1 year of age), or zanamivir (children older than 7 years of age).

Get the maximal benefit

For treatment of the flu, maximal benefit from the medications occurs if the medication is given within 48 hours, Hall says.

"For an exposure, the incubation period for flu is generally around one to three days. If a person were exposed to one individual with the flu and came to receive prophylaxis from their doctor four or five days later, most likely you wouldn’t use prophylaxis in that situation, because if they were going to get the flu, they would have already developed it," she says.

The situation was different when there was an outbreak of influenza in a local nursing home, she says. "Since there are multiple cases in an enclosed environment, there is no real time cutoff as to when you would start prophylaxis or when you wouldn’t. In that situation, you give everyone prophylaxis until the outbreak is resolved."

The patients in the nursing home are the only ones Hall knows who are on the antivirals now. "It’s not recommended that you use the antivirals to prevent flu in anyone who hasn’t gotten the vaccine. You would only use it in certain situations: In people who are high risk for complications of flu and who have been exposed to someone with the flu."