Said to get rid of the flu a day faster, the FDA says it has recorded several more deaths since CBS News first reported on the drug last month, for a total of 23 fatalities even before its second year on the market.
And while no conclusive link has been shown, the FDA is carefully watching over the next few months for any unusual pattern of side effects, especially breathing problems.
There are already dozens of cases in FDA "adverse event" reports obtained by CBS News.
"Immediately following his first dose," reads one, "the patient's (breathing trouble) worsened." On the third day, the problem was so bad, it was considered "life-threatening."
The patient's doctor and pharmacist wrote about the case in the New England Journal of Medicine, saying they did so because there's so little literature on the issue, and doctors often don't have time to read drug warning labels.
In the past year, GlaxoSmithKline, the drug's maker, agreed to issue a stronger label for Relenza because of serious adverse events, and sent a special warning letter to doctors.
But now, in a turnaround, the company says Relenza could actually be good for those with breathing trouble those patients considered by the FDA to be most at risk.
Dr. Kevin Murphy conducted a recent study on asthma patients for GlaxoSmithKline.
"We have not seen problems with the drug," said Murphy, of the Midwest Allergy and Asthma Clinic. "Those patients who were treated with Relenza actually had improvement of lung function during the first five days of therapy, compared with those who received no treatment."
Consumer advocate Dr. Sidney Wolfe still insists Relenza should never have been put on the market in the first place because, he says, it's never been proven to work.
"This drug was found to be so ineffective that the advisory committee that looked at the data voted 13-4 not to approve the drug," said Wolfe, of the group Public Citizen. "And yet they were overruled because of pressure from the company and officials higher up in the FDA."
FDA officials say they let Relenza on the market because when it comes to the flu, even a small potential benefit could be very important.
Whether it causes serious even fatal breathing trouble, or actually improves respiratory problems could well be answered from data collected by the FDA during this flu season.
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