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Electron MicrographView of Influenza A H1N1 Virions 

Two classes of antiviral drugs are available for the prevention and treatment of influenza: neuraminidase inhibitors and adamantanes, which inhibit a viral protein called M2. Influenza A H1N1, formerly known as swine flu, has been found to be resistant to adamantanes (amantadine and rimantadine). Oseltamivir (Tamiflu) and zanamivir (Relenza) are the two neuraminidase inhibitors currently available by prescription. These drugs reduce the median duration of symptoms by approximately one day and reduce the chance of contracting influenza by 70 to 90 percent when used for known influenza exposure.

Who Should be Treated with Neuraminidase Inhibitors if they Contract Swine Flu?

High risk groups for the development of H1N1 influenza A, formerly known as swine flu, include children and adolescents who are on longterm aspirin therapy (which puts them at risk for the brain abnormality Reye’s Syndrome if they contract influenza), children under the age of five and pregnant women. Adults and children with chronic lung disease, cancer, heart disease, kidney dysfunction, diabetes, sickle cell anemia, HIV infection and transplant recipients are also considered high risk for complications for influenza, and should be treated with antiviral agents.

Adults and children with brain abnormalities which result in decreased ability to clear respiratory secretions should also be treated with oseltamivir or zanamivir in the event they contract or are exposed to Influena A H1N1.  Patients with cerebral palsy, Lou Gehrig’s disease, seizure disorders and spinal cord injuries would be considered at higher risk for serious complications if they were to contract influenza. Elderly patients, especially those who live in Nursing Homes are also at high risk for developing complications of influenza.

Surprisingly, most patients to date who have contracted Influenza A H1N1, formerly known as swine flu, are younger, healthier patients. Use of Neuraminadase Inhibitors in Infants Under the Age of One Treatment should be considered for infants (down to one day of age) and children with moderate to severe influenza, and those at high risk of complications, including children younger than 5 years of age. While antiviral treatment earlier in the course of infection is likely to have a greater impact on decreasing clinical illness, treatment can be started even if the duration of illness is greater than 48 hours.

Who Should Receive Preventative Treatment with Neuraminidase Inhibitors?

The Centers for DIsease Control (CDC) recommends consideration of antiviral prophylactic (preventive) treatment with medications in patients who have had known or probable exposure to swine flu and are at high risk for developing complications if they were to contract influenza H1N1. Pregnant women, patients over the age of 65, and patients who have the above described chronic medical conditions and who are household contacts of a suspected or confirmed case of swine flu should receive treatment with antiviral medications. A patient is believed to be infectious from one day prior to seven days after symptoms of swine flu start.

Children in daycare and school children who are at high risk for complications of swine flu and who have had close contact with someone diagnosed with swine flu is eligible for prophylactic treatment with neuraminidase inhibitors.

Travelers to Mexico who are at high risk of influenza complications should also receive preventive treatment. Prophylactic treatment with antiviral agents is available to babies under the age of three months, but is only recommended if the infant is critically ill.

Ambulance personnel, emergency medical service providers, first responders, emergency room personnel and other health care workers who are working in areas of confirmed swine flu, and who are at risk of serious influenza related complications may receive antiviral medications to prevent influenza. People who are required to have contact with others in high risk situations such as hospitals or in areas with numerous documented cases of influenza A H1N1 cases should use N95 respirators  to prevent infection.

Viral Strains Resistant to Anti-Viral Medications are on the Rise

Antiviral resistance can develop to adamantanes such as rimantadine and amantadine after just two to three days of therapy with the class of antiviral agents called adamantanes. Amantadine is an example of this class of drug.

Resistance to oseltamivir, a neuraminidase inhibitor, can also form in two to three days of therapy. Resistance to neuraminidase inhibitors is being seen in some countries. It is expected that strains resistant to oseltamivir and zanamavir will be resistant to peramivir, another medication in the same class, which is currently in development.

Treatment with oseltamivir in infants under the age of one is based on age, not weight. Dosing of children between age one and twelve is based on weight. Zanamavir, which is an inhaled medication, should not be used in patients with asthma or chronic obstructive pulmonary disease (COPD) because it may cause wheezing or shortness of breath.

There have been rare reports of self-harming behavior that may be associated with neuraminidase inhibitor treatment, primarily in Japanese children. Therefore the risks and benefits of treatment with these anti-viral agents should be taken into account before they are used. Treatment or prevention with anti-viral agents does not negate the need for simple infection control measures such as hand washing to prevent the spread influenza H1 N1 infection.

Legal Disclaimer: This article is for informational purposes only and should not substitute for medical advice from your health care provider. The author is not providing personal medical opinion, diagnosis or course of treatment. Do not delay or substitute this information for medical treatment.

Last updated August 28, 2009 by Dr. Vee

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