FDA approves using Relenza to prevent flu

Mar 29, 2006 (CIDRAP News) – The US Food and Drug Administration (FDA) today approved the use of the antiviral drug zanamivir (Relenza) to prevent—not just treat—influenza in adults and children aged 5 and older.

Zanamivir, one of the two flu drugs known as neuraminidase inhibitors, was approved in 1999 for treating flu in people aged 7 and older, but not for prophylactic use. The other neuraminidase inhibitor, oseltamivir (Tamiflu), was approved for both treatment and prevention in adults and children from the age of 1 year.

"This approval is a welcome addition to the available defenses against the flu," Dr. Steven Galson, director of the FDA's center for Drug Evaluation and Research, said in an FDA news release. "This new use offers the medical community another option to prevent and control influenza A and B."

Many countries are stockpiling oseltamivir, made by Roche, in the hope that it will offer some help in the next flu pandemic. Stockpiling of zanamivir, made by GlaxoSmithKline, has been less prevalent, but the United States is stocking up on both.

"We have purchased, as of today, 4 million treatment courses of Relenza and 22 million treatment courses of Tamiflu," Bill Hall, a spokesman for the Department of Health and Human Services, told CIDRAP News today. "We expect all of them to be in the stockpile by the end of this calendar year."

Hall said HHS is aiming for a total of 81 million treatment courses of the two antivirals by 2008, with zanamivir making probably up about 20%.

Zanamivir is a powder that is inhaled by mouth with a "Diskhaler" device. Oseltamivir comes in capsule form.

Four large, placebo-controlled studies have shown the effectiveness of Relenza for preventing flu, the FDA reported. In two trials, the incidence of flu in households whose members received the drug was 4.1%, versus 19.0% in households where people received a placebo.

In a third trial, involving only adults, 2.0% of people in the Relenza group experienced flu symptoms, versus 6.1% of those in the placebo group, the FDA reported. In the fourth study, which involved mostly older adults, flu symptoms occurred in 1.4% of placebo group members and 0.2% of the treatment group.

The FDA said zanamivir has not been found effective for preventing flu in nursing homes. Also, it is not recommended as a substitute for flu vaccine, the primary tool for preventing flu.

The drug is not recommended for people who have asthma or other chronic respiratory disease, the FDA noted. After zanamivir's initial approval, bronchospasm, in some cases fatal, was reported in some patients, most of whom had asthma or chronic obstructive pulmonary disease, the agency said.

See also:

Mar 29 FDA news release
http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2006/ucm108622.htm

FDA background information on Relenza
http://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/ucm183783.htm

GlaxoSmithKline's detailed information on Relenza
http://us.gsk.com/products/assets/us_relenza.pdf

CIDRAP overview on use of antiviral agents for pandemic flu

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