Medical Health Encyclopedia

Note: Amantadine is a standard treatment for Parkinson’s disease and should be continued for that condition.

Anti-Viral Drugs: Neuraminidase Inhibitors

Brands and Benefits. Zanamivir (Relenza) and oseltamivir (Tamiflu) are called neuraminidase inhibitors. They are newer agents that have been designed to block a key viral enzyme, neuraminidase, which is involved with viral replication. According to a major review of over 50 studies published in 2006, these drugs are effective against the flu in about 60% of cases.

Both zanamivir and oseltamivir have the following benefits:

• Neuraminidase inhibitors are effective for treating both A and B strains of influenza. (M2 inhibitors are only effective against type A.)
• They shorten the duration of the flu by 1 to 3 days.
• They may help reduce transmission of the virus.
• They may have a lower risk than M1 inhibitors for emerging viral strains that are resistant to their effects.
• They have fewer serious side effects than the M2 inhibitors.
• Both have 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, they are much more expensive. They also need to be taken within 2 days of symptoms to be effective. Neither is effective against influenza-like illness. There are also some differences between the two agents that could be significant for some individuals:

• Zanamivir (Relenza) is administered as a nasal spray or 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. Of concern, however, was a 2001 British study, which found that a majority of elderly patients were not able to properly use the zanamivir (Relenza) inhaler device, making the medicine virtually ineffective in these cases. The study was small, however, and other reports suggest that zanamivir is sill effective in this older group.
• 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.