Influenza Treatments Zanamivir and Oseltamivir Not as Effective

Internal Medicine World ReportNovember 2014

Research teams examining the safety and efficacy of zanamivir and oseltamivir for influenza treatment concluded they are not as effective as popularly believed.

Both zanamivir (brand name Relenza) and oseltamivir (brand name Tamiflu) are not as effective, if effective at all, at treating influenza cases, according to 2 reports published in BMJ.

In the first, study, researchers examined the efficacy of zanamivir for influenza in adults and children by reviewing reports and regulatory comments in the current literature. They reviewed 28 trials in stage 1 and 26 trials in stage 2.

The researchers found zanamivir reduced the time to first alleviation of symptoms of influenza-like illnesses by 0.6 days, or about 14.4 hours. It also demonstrated a 10% decrease in average duration of symptoms of 6.6 to 6.0 days. However, in self reported and radiologically confirmed pneumonia, zanamivir did not reduce any risk. Zanamivir did not reduce hospital admission or death, but researchers did note its overall harmful events were minimal.

When reviewing zanamivir prophylaxis studies, researchers found individuals who demonstrated influenza-like symptoms were reduced when taking zanamivir, and 51 participants needed to be treated to prevent one case of influenza. But, the researchers pointed out, asymptomatic cases were not significant in individuals out households.

“Based on a full assessment of all trials conducted, zanamivir reduces the time to symptomatic improvement in adults (but not in children) with influenza-like illness by just over half a day, although this effect might be attenuated by symptom relief medication,” the authors concluded. “Zanamivir also reduces the proportion of patients with laboratory confirmed symptomatic influenza.”

For the second study, many of the same researchers wanted to determine oseltamivir’s safety and efficacy by reviewing clinical study reports of placebo trials and regulations in the current literature. They analyzed 23 trials in stage 1 and 20 in stage 2.

The researchers found oseltamivir in adults reduced first alleviation symptoms by 16.8 hours. The drug had no effect in children with asthma, though otherwise oseltamivir affected healthy children. There was no difference in adults between hospital admission and prophylaxis. Oseltamivir also reduced investigator mediated unverified pneumonia, but the effect was not statistically significant across 5 trials which detailed diagnostic confirmations of pneumonia.

In adults and children, oseltamivir increased the risk of vomiting; in adults alone, the risk of nausea, headaches, and renal events were increased on oseltamivir.

“In treatment studies oseltamivir also modestly reduces the time to first alleviation of symptoms, but it causes nausea and vomiting and increases the risk of headaches and renal and psychiatric syndromes,” the authors wrote. “The trade-off between benefits and harms should be borne in mind when making decisions to use oseltamivir for treatment, prophylaxis, or stockpiling.”

Overall, both studies draw attention to the risk of these drugs not doing the job of their intended use.

“Drug approval and use cannot be based on biased or missing information any longer,” study leaders said in a Cochrane press release. “We risk too much in our population’s health and economy. This updated Cochrane review is the first time a Cochrane systematic review has been based only on clinical study reports and regulator’s comments. It is the first example of open science in medicine using full clinical study reports available without conditions.”

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