Setback for AstraZeneca Drug

Updated from 10:04 a.m. EDT

A staff report by the Food and Drug Administration raised significant concerns Thursday about liver damage stemming from long-term use of an experimental drug made by AstraZeneca (AZN).

The staff report, issued a day before an FDA advisory committee meets to discuss the experimental blood thinner Exanta, could be a serious blow for the U.K.-based drug company.

The FDA staff report's documents on safety and efficacy on Exanta "look downright bad," said Dr. Tim Anderson, a drug industry analyst for Prudential Equity Group, in a research report to clients Thursday. "Prior to seeing the documents, we had forecasted odds of approval at 60/40. [The] odds may now be lower."

Anderson said his sales forecasts for Exanta are well below the Wall Street consensus, and "now even our estimates feel too high." He predicts Exanta's sales in 2008 will be $825 million vs. the consensus view of $1.6 billion. "Even if this drug gets approved, it is very likely that few physicians will use it unless additional [clinical] trial work were to show better results," he added.

AstraZeneca's stock was down $1.90, or 4%, to $45.15

AstraZeneca is seeking FDA approval for Exanta for three uses: preventing blood clots in veins for patients undergoing knee replacement surgery; preventing stroke and other clot-induced complications of the erratic heartbeat disease called atrial fibrillation; and long-term prevention of blood clots in veins after a patient has gotten a standard blood clot treatment.

AstraZeneca began marketing Exanta in Germany on June 21, having secured European Union regulatory approval in late 2003 for preventing blood clots in patients who had undergone elective hip or knee replacement surgeries. This is a narrow use of the drug, but it's also one for which liver problems would be less likely to arise because patients won't take the drug for a long time. The EU approval calls for the drug to be administered orally for 11 days.

The FDA staff report on Thursday indicated that there didn't appear to be any risk of liver damage -- measured by an increase in a liver enzyme -- during short-term use of Exanta. Short-term use is defined as less than 12 days.

But the agency also noted that company-sponsored tests of the drug during knee replacement surgery -- for which the drug would be used short term -- also revealed that elevated enzymes showed up in some patients six weeks after surgery. "Whether delayed onset of severe liver injury after short-term ... treatment could occur is unknown, since no additional routine study visits were conducted," the FDA said.

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