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Important points about the use of these drugs:
- The main benefit of these drugs is a reduction in the length of symptoms by about one day, and only when started within 48 hours after symptoms become evident. They may be used for treating both A and B strains of influenza.
- They may help reduce transmission of the virus.
- Both show some benefits for preventing influenza. Only oseltamivir has been approved for this purpose, however, and only in people over 13.
- They may reduce complications of influenza, although this needs to be confirmed. It is not yet known if they have any effect on overall survival rates.
- Oseltamivir is the only drug studied in avian flu cases. Although it is active in lab experiments, it has not been successful clinically. Experience is very limited, however, and it is not clear whether people infected with avian flu received the drug in time for it to be useful.
Limitations and Side Effects. Although they have many advantages compared to the M2 inhibitors, neuraminidase inhibitors are much more expensive. They also need to be taken within 2 days of the start of symptoms to be effective. Neither neuraminidase inhibitor is effective against influenza-like illness (one that is not caused by an influenza virus). There are also some differences between the two drugs that could be significant for some individuals:
- Zanamivir is administered through an inhaler. People with asthma or other lung disorders may experience airway spasms and should use this drug with caution. Side effects are generally minor in most patients. It is important to make sure that elderly patients are able to properly use the zanamivir inhaler device. Zanamivir should ONLY be used in its original inhaler device.
- Oseltamivir comes in capsule and liquid form. Side effects are also minor, but about 10 - 15% of patients experience nausea and vomiting. Patients with kidney dysfunction should take lower doses.
The current use of neuraminidase inhibitors in different age and patient groups is as follows:
- Adults: Both drugs are approved for treatment in adult patients.
- Children: Oseltamivir is approved for use in children age one and older. Studies report significant reduction in symptoms and in the incidence of ear infections in this population. The American Academy of Pediatrics recommends the following: Therapy should be provided to children with influenza infection who are at high risk of severe infection, and to children with moderate-to-severe influenza infection who may benefit from a decrease in the duration of symptoms. Prophylaxis should be provided (1) to high-risk children who have not yet received immunization and during the 2 weeks after immunization, (2) to unimmunized family members and health care professionals with close contact with high-risk unimmunized children or infants who are younger than 6 months, and (3) for control of influenza outbreaks in unimmunized staff and children in an institutional setting.
- High-risk Patients. Recent studies indicate neuraminidase inhibitors are safe and effective in patients with serious medical problems or other conditions that put them at risk for complications of flu.
A third neuroaminidase product, peramivir, is now in clinical trials. However, it was authorized as emergency treatment for severely ill, hospitalized patients with H1N1 "swine" flu. This authorization was terminated in June 2010. Peramivir is given intravenously.
Anti-Viral Drugs: M2 Inhibitors
Brands and Benefits. Amantadine (Symmetrel) and rimantadine (Flumadine) are M2 inhibitors. The following benefits may apply to the minority of strains of influenza A that remain sensitive to the drugs:
- Both offer some protection against influenza A and prevent severe illness if a person contracts the infection. (To be effective, it must be administered within 2 days of onset.)
- They may shorten the duration and lessen the severity of the flu if given within 48 hours of onset of symptoms.
Limitations. Drawbacks of M2 inhibitors include:
- They are not effective against the 2010-2011 flu strains.
- Viral resistance to these agents is rapidly increasing.
- M2 inhibitors are not effective against influenza B.
- Neither drug has proven to reduce the risk for complications of the flu, including pneumonia and bronchitis.
Side Effects. Both M2 inhibitors occasionally cause nausea, vomiting, indigestion, insomnia, and hallucinations. Amantadine affects the nervous system and about 10% of people experience nervousness, depression, anxiety, difficulty concentrating, and lightheadedness. Rimantadine is less likely to do so. Rarely, amantadine can cause seizures.
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Review Date: 01/29/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine,
Harvard Medical School; Physician, Massachusetts General Hospital.
Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M.,
Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)
