Drugs That Fight the Flu by Alice A. McCarthy, MBA

En Español (Spanish Version)

Estimates vary, but approximately 5%-20% of the US population get the seasonal flu each year. Although most of us struggle through it and feel better in about a week, about 36,000 people die from it in the US each year. They are usually the elderly, infants, and people with chronic illness. As the weather turns cold and the virus increases its activity, your doctor or public health officials in your community may recommend antiviral medications.

Antiviral Prescription Medicines

Amantadine and Rimantadine

There are three types of influenza virus that affect humans: A, B, and C. The first two, A and B, cause the most serious illness. Amantadine and rimantadine have long been available to control symptoms of influenza caused by the type A virus.These closely related drugs, when given within the first 48-72 hours of becoming sick (or in some circumstances even before exposure to the illness), can reduce the severity and duration of influenza. Note that amantadine and rimantadine, while still effective for seasonal flu, do not work against the pandemic H1N1 flu.

There is no consistent difference in symptoms between the two influenza types, and testing may not always be available to help decide whether or not these drugs will work. Both drugs can affect the central nervous system and cause undesirable side effects. These are more common with amantadine. Drug resistance to these medications is also common, meaning that they may not work for some flu-infected people, particularly those in nursing homes or hospital settings.

Relenza

Zanamivir (Relenza) was the first drug approved for treatment of both influenza A and B. The US Food and Drug Administration (FDA) approved Relenza for treatment in people seven years or older who have been symptomatic for no more than two days.

In a US trial of 780 people, treatment with Relenza, when initiated within 48 hours of the onset of symptoms, reduced the normal seven-day flu course by only one day. But studies conducted outside the US have suggested that Relenza could reduce flu symptoms by as much as 2-2.5 days. People with more severe symptoms are more likely to notice improvement.

Prevention

Relenza is also used to prevent influenza virus A and B infection in people five years and older. A study found that Relenza prevented the spread of the flu virus between family members in 79% of study participants. Among 337 families studied, only 4% had one or more family members contract the flu after treatment, compared with 19% of those taking a placebo. The study's lead scientist, Frederick Hayden, MD, said that although the annual flu vaccine is the best way to prevent the disease, "with Relenza we have an additional way to prevent the disruption that influenza can cause in families."

Inhaled Medication

Relenza is an inhaled treatment that is given by a breath-activated device called the Diskhaler, which delivers the drug directly into the lungs, the site of an influenza infection. When used twice a day for five days, Relenza prevents the natural cycle of the flu by interfering with an enzyme called neuraminidase. The medication blocks the ability of the flu virus to attack your cells.

Side Effects

In clinical studies, only about 3% of patients experienced sinusitis, diarrhea, or nausea—the three most common side effects identified so far. Asthma patients are the exception. Relenza may worsen asthma or chronic obstructive pulmonary disease (COPD). Some patients with mild or moderate asthma suffer an acute shutting down of the airway (called bronchospasm) after inhaling Relenza. Because of the risk of bronchospasm, the FDA specifically states that Relenza may carry a risk in patients with severe or decompensated asthma or chronic obstructive pulmonary disease (COPD).

On January 12, 2000, the FDA issued a public health advisory alerting healthcare professionals that it had received several reports of deterioration of respiratory function following inhalation of Relenza in patients with underlying asthma or chronic obstructive pulmonary disease (COPD). As a result, the FDA recommended that "in such patients, Relenza should be used under conditions of careful monitoring, proper observation and appropriate supportive care, including the availability of short-acting bronchodilators."

Unfortunately, even some people who do not have known asthma will develop bronchospasm after using Relenza. This side effect may be severe enough to require medical treatment.

Tamiflu

Oseltamivir (Tamiflu) is from the same family of drugs as Relenza and acts in a similar way. It is given in pill form, rather than inhaled, and as a result, is free from the respiratory side effects that plague Relenza. Tamiflu is used in the treatment and prevention of influenza A and B in people aged one year or older. In the US, some kinds of seasonal influenza viruses are resistant to Tamiflu, but it can be used for pandemic H1N1 flu, for which it may be given to infants less than one year old. Also, scientists think that oseltamavir may prove to be a crucial tool for limiting the spread of avian (bird) influenza if it becomes more widespread among human populations.

In one of two studies published in the Journal of the American Medical Association in 1999, Tamiflu reduced symptoms and duration of the flu by about half in 56 unvaccinated adults voluntarily infected with the virus. However, across all studies, the drug shortens the flu by an average of 1-1½ days.

In terms of prevention, in the second Tamiflu study, only 38% (8 of 21) of those taking the drug were infected when exposed to the virus, compared with 67% (8 of 12) who didn't receive the medicine.

Peramivir

Peramivir is an experimental medicine used to treat pandemic H1N1 flu. It is experimental because the FDA has not approved it. However, the FDA has allowed doctors to use the medicine on hospitalized patients with H1N1 flu if other antiviral medicines do not work.

The medicine is given through an IV (needle in the vein) one time each day for five days or more. Peramivir may cause diarrhea, nausea, vomiting, and a decrease in white blood cells. Since researchers are still studying the effects of the medicine, there may be other side effects that are not yet known.

Antiviral Medications For Flu Prevention

If you have the flu and live with someone who is at risk for complications (eg, elderly, babies, someone with cancer), that person may need to take antiviral medications to prevent getting the flu from you.

Vaccine Best Means to Avoid Infection

The best way to avoid the flu altogether is to get vaccinated. Dr. Hayden, who has studied Relenza and Tamiflu extensively, believes that these new drugs aren't a substitute for the flu vaccine. The annual flu shot contains inactivated viruses—type A virus (H3N2), type A virus (H1N1), type B virus—that change each year depending on the predominant strains in circulation. The strain for the pandemic H1N1 (2009) flu is included in the 2010-11 seasonal flu vaccine. You do not need to have a separate shot for pandemic H1N1 (2009) flu.

You should get vaccinated between September and January (or later since the flu season can last much longer).