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Zanamivir slightly decreases flu symptom duration; prophylaxis is more effective

Clinical Question:
Is zanamivir effective in relieving symptoms in patients with confirmed or suspected influenza?

Bottom Line:
As a treatment for influenza, zanamivir (Relenza) decreases the duration of symptoms by less than a day in adults. It does not affect the likelihood of pneumonia developing in either adults or children. As a prophylactic, zanamivir is effective in preventing symptomatic influenza development in adults and the development of pneumonia in both adults and children. Adverse effects are not more likely than with placebo treatment. (LOE = 1a)

Heneghan CJ, Onakpoya I, Thompson M, Spencer EA, Jones M, Jefferson T. Zanamivir for influenza in adults and children: systematic review of clinical study reports and summary of regulatory comments. BMJ 2014;348:g2547.  [PMID:24811412]

Study Design:
Meta-analysis (randomized controlled trials)


Various (meta-analysis)

The authors of this meta-analysis identified 26 studies conducted using Cochrane methods supplemented with data provided from the manufacturer. They included only randomized controlled trials, often having to decide whether to use published results or different, unpublished results of the same study from the manufacturer. Two authors independently selected articles for inclusion. There were issues in most of the studies regarding randomization and masking. For treatment of adults, zanamivir reduced the duration until the first alleviation of symptoms from 6.6 days to 6.0 days. The likelihood of pneumonia was not affected by treatment in either adults or children. When taken a prophylactic, zanamivir reduced the likelihood of influenza from 3.26% to 1.27% (number needed to treat = 51; 95% CI, 40-103) and decreased the likelihood of pneumonia in adults, but not children.


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