Oseltamivir is taken as a pill twice each day for 5
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
- Zanamivir is used for people age 7 and
- Oseltamivir is used to treat flu in people age 1 or
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
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
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
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.
Some minor side effects of zanamivir and
- 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).
A small number of people, especially children, have shown
behavior changes after taking oseltamivir or zanamivir.4, 5 These include:
- Attempts to hurt themselves.
- Confusion or
Anyone who takes Tamiflu or Relenza, especially children,
should be watched closely. If the person seems confused, tries to hurt himself
or herself, or is acting strangely, call a doctor right away.
Drug Reference for a full list of side effects. (Drug Reference is not
available in all systems.)
What To Think About
oseltamivir work best when started within 48 hours of your first flu
Some people who have
chronic obstructive pulmonary disease (COPD) and use
zanamivir may experience reduced lung function and have trouble breathing.
If you have these conditions, talk to your doctor about whether you should use
The influenza virus A can develop
resistance to the antiviral flu medicines amantadine
and rimantadine. Although influenza viruses A and B have not developed
resistance to zanamivir or oseltamivir at this time, resistance is possible
with increased use of these medicines.
Of the four antiviral flu
medicines, zanamivir and oseltamivir are the most expensive.
Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.
Shun-Shin M, et al. (2009). Neuraminidase inhibitors for treatment and prophylaxis of influenza in children: Systematic review and meta-analysis of randomised controlled trials. BMJ. Published online August 11, 2009 (doi: 10.1136/bmj.b3172).
Cooper NJ, et al. (2003). Effectiveness of
neuraminidase inhibitors in treatment and prevention of influenza A and B:
Systematic review and meta-analyses of randomised controlled trials.
BMJ, 326(7401): 1235.
Treanor JT, et al. (2000). Efficacy and safety of the
oral neuraminidase inhibitor oseltamivir in treating acute influenza.
JAMA, 283(8): 1016-1024.
U.S. Food and Drug Administration (2006). Safety
alert: Tamiflu (oseltamivir phosphate). FDA Safety Information and Adverse Event Reporting Program. Available online:
U.S. Food and Drug Administration (2008). Safety
alert: Relenza (zanamivir). FDA Safety Information and Adverse Event Reporting Program. Available online:
Monto AS, et al. (2002). Zanamivir prophylaxis: An
effective strategy for the prevention of influenza types A and B within
households. Journal of Infectious Diseases, 186(11):