Zanamivir

Zanamivir is a prescription drug used for the treatment of influenza ("the flu"). In July 1999, it became the first commercially marketed neuraminidase inhibitor. Neuraminidase inhibitors prevent the spread of virus cells from one cell to another. Other neuraminidase inhibitors include oseltamivir (Tamiflu) and peramivir.

Other Names

Zanamivir is marketed as Relenza by GlaxoSmithKline.

Uses

Zanamivir is used to treat infection with the influenza A or B virus in people 7 years of age and older who have had symptoms for no more than 2 days. It is also used to prevent infection in people 5 years of age or older.

How Zanamivir is Taken

Zanamivir is provided in an oral inhaler. The recommended dose for treatment of influenza is 10 mg twice daily (12 hours between doses) over five days. The recommended dose to prevent infection is 10 mg once daily over 10 days in a household setting and over 28 days in a community setting (e.g., hospital or nursing home).

How Zanamivir Works

Influenza viruses depend on an enzyme called neuraminidase to spread infection to other cells. Neuraminidase cleaves proteins on the surface of cells and the virus itself. This cleavage allows the virus particles to bud from cells and infect other cells. Zanamivir inhibits neuraminidase. By inhibiting this enzyme, zanamivir causes the viruses to collect at the surface of cells, and thus prevents the spread of infection.

Viruses can develop resistance to zanamivir. The most common mechanism underlying resistance is altered structure of neuraminidase or the proteins it cleaves. However, zanamivir is effective against some viruses that are resistant to treatment with other neuraminidase inhibitors.

How the Body Affects Zanamivir

Peak circulating levels are zanamivir are reached within one to two hours post-inhalation. The concentration of the drug in the blood is reduced by half in 2.5–5 hours. Most zanamivir is not metabolized; over 90% of the drug is excreted unchanged in the urine.

Side Effects

Zanamivir is very well-tolerated in the majority of patients because neuraminidase is only used by viruses.

Risks and Precautions

The greatest risk associated with zanamivir use is lung toxicity resulting from inhalation. Zanamivir can cause wheezing or shortness of breath in people with or without underlying lung conditions such as asthma or chronic obstructive pulmonary disease. For those with underlying lung disease, these reactions can be fatal.

Zanamivir has also been associated with neurological reactions.(see video below)

Drug Interactions

No significant interactions with zanamivir have been reported to date.

Research

In one clinical trial, the percent of patients with the flu was reduced from 1.4% of those on placebo to 0.2% for those who used Zanamivir.^[1]

A multicenter trial examined the effectiveness of zanamivir for the prevention of influenza in families.^[2] Influenze infection occurred in at least one family member in 4% of families treated with zanamivir and 19% of families treated with placebo.

References

1. ↑ Senior Journal Relenza Inhaler Approved for Prevention of A and B Flu; Stockpiled for Pandemic
2. ↑ Hayden FG, Gubareva LV, Monto AS, et al. Inhaled zanamivir for the prevention of influenza in families. Zanamivir Family Study Group. N Engl J Med. 2000 Nov 2;343(18):1282-9. Abstract | Full Text | PDF

External Links

FDA: Patient Information Sheet