Review Challenges Tamiflu Efficacy

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The oseltamivir analysis showed:

The time to first alleviation of symptoms in people with influenza-like illness was a median of 160 hours in the placebo groups and about 21 hours shorter in those treated with oseltamivir. The difference, evaluated in five studies, was significant at P<0.001.

There was no evidence of effect on hospital admissions: In seven studies, the odds ratio was 0.95, with a 95% confidence interval from 0.57 to 1.61, which was non-significant at P=0.86.

A post-protocol analysis of eight studies showed that oseltamivir patients were less likely to be diagnosed with influenza.

The data "lacked sufficient detail to credibly assess" any effect on influenza complications and viral transmission.

Data Discrepancies Found

But discrepancies between the published trial data and the clinical study reports "led us to lose confidence in the journal reports," Doshi and colleagues wrote in BMJ.

For example, they noted that one journal report clearly said there were no drug-related serious adverse events, but the clinical study report listed three that were possibly related to oseltamivir.

As well, the sheer scope of the clinical study reports meant that much was left out of journal reports. One 2010 study, on safety and pharmacokinetics of oseltamivir at standard and high dosages, took up seven journal pages and 8,545 pages of the clinical study report.

But the researchers were also shaken, they said, by the "fragility" of some of their assumptions.

For instance, they found that the clinical study reports showed that in many trials, the placebo contained two chemicals not found in the oseltamivir capsules.

"We could find no explanation for why these ingredients were only in the placebo," they wrote in BMJ, "and Roche did not answer our request for more information on the placebo content."

Jefferson and colleagues also reported they found disparities in the numbers of influenza-infected people reported to be present in the treatment versus control groups of oseltamivir trials.

One possible explanation, they noted, is that oseltamivir affects antibody production -- even though the manufacturer says it does not.

Gaps in Knowledge Remain

That question is profoundly important, Doshi told MedPage Today, because it may offer clues to how the drug works -- one of the gaps in knowledge about oseltamivir.

"You can't make good therapeutic decisions if you don't know how the drugs works," he said -- information that he and his colleagues suspect may be buried in the mass of missing data.

It's also important, he said, because public health agencies have been making decisions to stockpile oseltamivir without a clear understanding of the facts.

Essentially, he said, those decisions have been based on the flawed study -- a Roche-supported meta-analysis -- that was thrown out of the 2009 Cochrane review.

"They're taking the drug manufacturer's word at face value," he said.

The results seem unlikely to resolve conflicts over the medical value of the drug, which is a major cash cow for Roche, adding some $3.4 billion to the company's bottom line in 2009 alone, according to Deborah Cohen, investigations editor of BMJ.

In an accompanying article, Cohen said that "clinicians can be forgiven for being confused about what the evidence on oseltamivir says."

She noted that the European Centre for Disease Prevention and Control, the CDC, and the World Health Organization "differ in their conclusions about what the drug does."

As well, those conclusions are often contradicted by claims on the drug labels -- themselves allowed by regulators, Cohen argued.

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