Relenza Now Approved for Prevention of Influenza A and B
By Luciana L. Borio, M.D. and John G. Bartlett, M.D., April 3, 2006
On March 29, 2006 the Food and Drug Administration approved  the neuraminidase inhibitor Relenza (zanamivir) for the prevention of influenza A and B in adults and children over the age of 5 years. Previously, Relenza was approved only for the treatment of influenza, whereas Tamiflu (oseltamivir), the only other neuraminidase inhibitor that is commercially available, was approved for both the treatment and prevention of influenza.
Relenza’s effectiveness has been demonstrated in at least three randomized, placebo controlled, clinical studies. In two of these, Relenza reduced the spread of influenza in households:
Monto and colleagues  conducted a study in which Relenza 10 mg inhaled daily x 10 days, or placebo was administered to household contacts 5 years or older once one of the household members was suspected to have influenza (index patient). The index patient was not treated. In total, 245 households received Relenza, and 242 households received placebo. Only 4% of Relenza households versus 19% of placebo households (P<0.001) had at least one contact who developed symptomatic, laboratory confirmed influenza.
Hayden and colleagues  conducted a study similar in design, except that index patients were also randomized to receive either placebo or Relenza 10 mg twice a day x 5 days. Family members received either placebo or Relenza prophylaxis, as in Monto’s study. Again, 4% of Relenza households versus 19% of placebo households (P<0.001) had at least one contact who developed symptomatic, laboratory confirmed influenza.
In another study by Monto and colleagues, Relenza was shown to reduce the incidence of influenza in persons who lived in communities experiencing an influenza outbreak. The authors examined the efficacy of prophylactic Relenza in 1107 healthy adults; 554 were randomized to receive Relenza and 553 to receive placebo for 4 weeks, beginning before the start of that year’s influenza season. Relenza was 67% efficacious in preventing laboratory-confirmed clinical influenza. Illness developed in 6.1% in the placebo group vs. 2% in the treatment group.
Whereas Tamiflu is administered orally, Relenza is inhaled as a dry powder, administered via a disk inhaler. Bronchospasm, especially in patients with asthma or chronic obstructive pulmonary disease, and at times associated with death, has been reported in patients receiving Relenza. Therefore, Relenza is not recommended for patients with underlying pulmonary disease. The package insert  alerts that the drug “should be discontinued in any patient who develops bronchospasm or decline in respiratory function.”
Both Tamiflu and Relenza are being stockpiled by the federal government to be used in the event of an influenza pandemic. A potential benefit of Relenza is that it is active in vitro against influenza A strains that are resistant to oseltamivir due to the amino acid substitution in codon 274, the mutation noted in the resistant H5N1 strains in Vietnam .
FDA Approves a Second Drug for the Prevention of Influenza A and B in Adults and Children. (Accessed March 30, 2006, at https://www.ptcommunity.com/news/2006-03-29-000000/second-drug-approved-prevention-influenza-and-b-adults-and-children.)
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Relenza (zanamivir for inhalation): prescribing information. (Accessed March 30, 2006, at http://us.gsk.com/products/assets/us_relenza.pdf.)
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