Examples

Oseltamivir is taken as a pill twice each day for 5 days.

Zanamivir is inhaled through a device called a Diskhaler. This inhaler device delivers the medicine to the lungs, where the influenza (flu) virus multiplies. It is inhaled twice a day for 5 days.

How It Works

Zanamivir and oseltamivir are medicines known as neuraminidase inhibitors. They help prevent influenza A and influenza B viruses from multiplying in the body by interfering with the production and release of virus from cells that line the respiratory tract. This may slow the spread of the infection within the airways and lungs.

Why It Is Used

Zanamivir and oseltamivir may be used to treat flu caused by both the influenza A and B viruses.

• Both medicines are given twice a day for 5 days.
• Zanamivir is used for people age 7 and older.
• Oseltamivir is used to treat flu in people age 1 or older.

The U.S. Food and Drug Administration (FDA) has also approved oseltamivir to prevent flu in adults and children age 13 and older. Zanamivir is approved for use to prevent the flu in adults and children age 5 and older.

How Well It Works

Both zanamivir and oseltamivir have been shown to effectively treat and prevent the flu.² Using one of these medicines typically shortens the course of influenza A or B by at least 1 day.^{2, 1}

A well-controlled study found that oseltamivir taken within 36 hours of the first flu symptoms reduced the length of illness by 30%, the severity by 40%, and the time to resume normal activities by 2 or 3 days. These results are compared with people who had treatment with a placebo.³

Zanamivir has been shown to prevent flu among household members when a member of the family is infected.⁶

Zanamivir and oseltamivir may not be as effective for people who do not have a fever or do not have severe flu symptoms. And more study is needed to find out how well these medicines work to prevent the flu in people who have severely impaired immune systems.

Side Effects

Some minor side effects of zanamivir and oseltamivir include:

• Diarrhea.
• Nausea and vomiting. This side effect tends to occur with oseltamivir. Taking the medicine with food may reduce the risk.
• Swelling of the sinuses (sinusitis).