A new review of medical evidence continues to raise questions about the safety and effectiveness of the influenza drug Tamiflu, which the United States and other nations have spent billions of dollars to stockpile for use in a possible flu pandemic.
The review concluded that Tamiflu could reduce the duration of flu symptoms by about 21 hours, from the typical six or seven days. But the reviewers said they could not confirm two other purported effects of the drug often cited as reasons for using it in a pandemic – that it reduced complications of flu, like pneumonia or hospitalizations, and that it reduced transmission of the virus.
The reviewers said that their analysis was hampered by the fact that the drug’s manufacturer, Roche, had not supplied all the data from clinical trials that it had promised to provide.
“To this day, we have not received a single full study report from Roche,’’ said Peter Doshi, a postdoctoral fellow at the Johns Hopkins University School of Medicine and a co-author of the new review, which was published Tuesday by the Cochrane Collaboration, an international group of volunteer researchers who study medical evidence.
The new review said that data on 60 percent of the patients in the clinical trials of Tamiflu had never been published in medical journals. “If we look only at published reports, the extreme danger is that we are going to arrive at conclusions that are biased and that nobody should trust,’’ Mr. Doshi said.
The Cochrane Collaboration has reviewed the evidence on Tamiflu in the past, and it has clashed with Roche before over access to data. The new review was financed by the National Institute for Health Research in Britain.
Roche said in a statement that it had provided the Cochrane group with “3,200 pages of very detailed information, enabling their questions to be answered,’’ and that it had made full study data available to regulatory authorities.
The company, which is based in Switzerland, also defended the effectiveness of Tamiflu, which is known generically as oseltamivir and which it licensed from Gilead Sciences.
“Numerous clinical trials and real-life medical experience show Tamiflu is effective in reducing the severity and duration of influenza symptoms as well as specified secondary complications,’’ Roche’s statement said. “Analyses by health authorities and independent research groups show that, during the 2009 H1NI pandemic, Tamiflu saved lives and reduced hospitalization.’’
The Centers for Disease Control and Prevention and the Department of Health and Human Services have in the past cited the reduction in complications like pneumonia as reasons for stockpiling the drug. The federal government has spent at least $1.5 billion to build supplies of Tamiflu and other anti-influenza drugs.
Much of the previous evidence suggesting that Tamiflu was effective against flu complications came from combining the results of 10 clinical trials into a so-called meta-analysis, which was published in 2003. Based largely on that meta-analysis, which had been published in 2003, the Cochrane Collaboration in 2006 concluded that Tamiflu could reduce flu complications.
But a reader later pointed out that only two of the 10 studies included in the meta-analysis had been independently published. In 2009, the Cochrane researchers, relying on only those two published studies, concluded that there was not solid evidence that Tamiflu reduced complications.
For the latest analysis, published Tuesday, the group decided not to rely on published papers and to instead rely on rather raw data from clinical trials. It received thousands of pages, mainly from the European Medicines Agency.
The new review concluded that there was no reduction in hospitalization. It also said that the raw data contained more reports of possible side effects, like headaches and psychiatric problems, than were mentioned in published papers describing clinical trial results.
Roche, in its statement, said side effects were listed on the drug’s labels.