Colds and the Flu - Medications

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Anti-Viral Drugs: Neuraminidase Inhibitors

Brands and Benefits. Zanamivir (Relenza) and oseltamivir (Tamiflu) are neuraminidase inhibitors. They are newer agents that have been designed to block a key viral enzyme, neuraminidase, which is involved with viral replication. While effective, their overall benefit is modest.

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.

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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.