- All four of the antiviral medications (amantadine, rimantadine, zanamavir and oseltamivir) may be effective for influenza A viruses. Unfortunately, a high proportion of currently circulating influenza A viruses in the United States are resistant to amantadine and rimantadine. It is now recommended that neither amantadine nor rimantadine be used for the treatment or chemoprophylaxis of influenza A in the United States until susceptibility to these antiviral medications has been re-established among circulating influenza A viruses.
Only oseltamivir and zanamivir are effective for both influenza A & B viruses.
- Antiviral medications are often used to help control influenza outbreaks in institutions, such as nursing homes, hospital wards, and even cruise ships.
- Treatment - Oseltamivir is approved for treatment of persons aged >1 year, and zanamivir is approved for treatment of persons aged >7 years.
- Prevention (chemoprophylaxis) - High risk individuals and unvaccinated persons caring for high risk individuals may be prescibed antiviral medications. Chemoprohylaxis is intended to reduce the risk of contracting or passing on the virus. One 6-week study of oseltamivir chemoprophylaxis among nursing home residents reported a 92% reduction in influenza illness.
Oseltamivir and zanamivir can be used for chemoprophylaxis of influenza; oseltamivir is licensed for use in persons aged >1 year, and zanamivir is licensed for use in persons aged >5 years
- High risk individuals that may benefit from antivirals include:
- people 65 years of age and older
- children 12-23 months of age
- people with chronic medical conditions (for example, heart or lung disease, diabetes, immunosuppressed)
- pregnant women
- individuals who are unable to be vaccinated
- Antiviral side effects
- Zanamivir
- Renal impairment decreases clearance and increases systemic exposure
- Not recommended for treatment for patients with underlying airway disease due to increased risk of bronchospasm
- The most common adverse events reported are diarrhea; nausea; sinusitis; nasal signs and symptoms; bronchitis; cough; headache; dizziness; and ear, nose, and throat infections.
- Oseltamivir
- On November 13, 2006, FDA approved a labeling supplement for Roche Laboratories’ Tamiflu (Oseltamivir Phosphate) to include a precaution about neuropsychiatric events. The revision is based on postmarketing reports (mostly from Japan) of self-injury and delirium with the use of Tamiflu in patients with influenza. The reports were primarily among pediatric patients.
- Nausea and vomiting
- Renal impairment decreases clearance and increases systemic exposure
- Pregnancy
- Because of the unknown effects of influenza antiviral drugs on pregnant women and their fetuses, these two drugs should be used during pregnancy only if the potential benefit justifies the potential risk to the embryo or fetus.
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