Drugs That Fight the Flu
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. In addition to the seasonal flu, experts are preparing for the effects of a new worldwide pandemic, caused by the ]]>pandemic H1N1 (2009) flu virus]]> (also referred to as swine flu). Fortunately, in the US, the pandemic H1N1 virus has caused symptoms no worse the the typical seasonal flu since it first appeared in the spring. Nevertheless, 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 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.
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.
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."
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.
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.
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]]> 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
Sometimes it is beneficial to take antiviral medications to prevent the flu. You may want to talk with your doctor about taking antiviral medications to lower your risk of getting the flu if you are exposed to the flu and:
- Are at high risk for complications of the flu
- Are a healthcare worker, public health worker, or first responder
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. Importantly, the annual vaccine, designed to lower the risk of seasonal influenza, is not effective against pandemic H1NI influenza. Vaccines effective against the pandemic H1N1 flu will be available in October 2009.
Anyone who wants to reduce their risk of the flu should consider the vaccine. Those who should get a yearly flu vaccine include:
- Children six months-19 years old
- Parents, babysitters, and caretakers of children less than six months old (as these children are too young to be vaccinated)
- Adults older than 50 years of age (shown to reduce hospitalizations and deaths in older adults) *
- Those living or working in nursing homes and long-term care facilities
- Those with chronic medical conditions (eg, diabetes or disorders of the liver, lungs, heart, kidneys, blood or immune system)
- Women who are pregnant
- Healthcare workers
- Those living with someone who is at high risk for complications from the flu
There are people, however, who should not be vaccinated:
- Those who are severely allergic to chicken eggs
- Those who have had a severe reaction to vaccination in the past
- Those who have had ]]>Guillain-Barré syndrome]]> within six weeks of getting vaccinated previously
- Children less than six months old
You should get vaccinated between September and January (or later since the flu season can last much longer).
Centers for Disease Control and Prevention
National Institute of Allergies and Infectious Diseases
Public Health Agency of Canada
Centers for Disease Control and Prevention. Emergency use authorization of peramivir fact sheet for patients and parents/caregivers. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/h1n1flu/eua/peramivir.htm. Created October 23, 2009. Accessed November 4, 2009.
Centers for Disease Control and Prevention. Key facts about antiviral drugs and influenza (flu). Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/flu/protect/antiviral/keyfacts.htm. Updated April 7, 2009. Accessed September 1, 2009.
Centers for Disease Control and Prevention. Key facts about seasonal flu vaccine. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/FLU/protect/keyfacts.htm. Updated December 10, 2008. Accessed September 1, 2009.
Centers for Disease Control and Prevention. Key facts about seasonal influenza (flu). Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/flu/keyfacts.htm. Updated March 12, 2009. Accessed September 1, 2009.
Centers for Disease Control and Prevention Health Advisory. Distributed via Health Alert Network. December 19, 2008.
DynaMed Editors. Influenza antiviral treatment and prophylaxis. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed/what.php. Updated March 29, 2010. Accessed April 1, 2010.
DynaMed Editors. Pandemic (H1N1) 2009. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed/what.php. Updated November 3, 2009. Accessed November 4, 2009.
Flu fact sheet. National Institutes of Health website. Available at: http://www.niaid.nih.gov/factsheets/flu.htm.
Flu information. Centers for Disease Control website. Available at: http://www.cdc.gov/ncidod/diseases/flu/fluviral.htm.
Flu information. World Health Organization website. Available at: http://oms.b3e.jussieu.fr/.
Hayden FG, et al. Use of the oral neuraminidase inhibitor oseltamivir in experimental human influenza: randomized controlled trials for prevention and treatment. JAMA. 1999 Oct 6;282:1240-1246.
Monto AS, et al. Zanamivir in the prevention of influenza among healthy adults. JAMA. 1999 Jul 7;282: 31-35.
Relenza website. Available at: http://www.relenza.com.
* 10/15/2007 DynaMed Systematic Literature Surveillance http://www.ebscohost.com/dynamed/what.php: Nichol KL, Nordin JD, Nelson DB, Mullooly JP, Hak E. Effectiveness of influenza vaccine in the community-dwelling elderly. N Engl J Med. 2007;357:1373-1381.
Last reviewed September 2009 by ]]>Richard Glickman-Simon, MD ]]>
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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