A new review is questioning the effectiveness of two key drugs enlisted in the fight against influenza and in turn the investments by governments to stockpile the drugs in the event of a global flu outbreak.
The antiviral drugs Tamiflu (oseltamivir) and Relenza (zanamivir ) are commonly used to treat influenza in healthy adults and children.
In the case of Tamiflu, the drug does shorten symptoms of influenza by about half a day – as the manufacturer suggests – but there is insufficient evidence to support claims that it reduces hospital admissions or serious complications, such as confirmed pneumonia or bronchitis, says the review published today by The Cochrane Collaboration, a non-profit, international health-care research network, and the British medical journal BMJ.
The review also cites evidence from treatment trials (when the drug was given for about five days) that Tamiflu increased the risk of nausea and vomiting in adults by around 4% and in children by around 5%.
And evidence from prophylaxis or prevention trials (when the drug was given for about six weeks) showed Tamiflu use was related to increased risks of headaches, psychiatric disturbances, especially depression and confusion, and renal problems.
The review of studies related to the nasal spray Relenza found fewer adverse effects compared with Tamiflu, but also showed no effectiveness against flu complications or reducing hospitalizations.
Although Relenza, likewise reduced symptoms by about half a day, the reviewers report “that it may be no better than other symptom relief medications,” such as drinking clear liquids, gargling with warm salt water, and using saline nasal drops, over-the-counter decongestants, and pain relievers such as acetaminophen and ibuprofen.
In a statement, Relenza-maker GlaxoSmithKline says, “We continue to believe the data from Relenza’s clinical trial (program) support its effectiveness against flu and that when used appropriately, in the right patient, it can reduce duration of flu symptoms.”
Tamiflu-maker Genentech, a division of Roche, also challenged the review’s conclusions, noting that the researchers focused on only 20 out of 77 clinical trials, “all made available to them,” and excluded “real-world data” from non-Roche-sponsored observational trials.
In some cases, the reviewers also failed to analyze the appropriate statistical information, which “doesn’t give you an accurate representation of what the true effect of the medicine is,” says Barry Clinch, principal clinical scientist with Roche.