Study finds deaths of Zilmax-fed cattle dwarf Merck's official reports to FDA

Courtesy of Merck

Last August, Merck ($MRK) stopped selling livestock drug Zilmax on worrisome side-effect reports. Now it appears the feed additive triggered problems well beyond those reported at the time.

As new research findings indicate, the number of U.S. cattle deaths linked to Zilmax could reach into the thousands. That's far higher than the figures Merck reported to the FDA, Reuters reports. And it could seriously interfere with Merck's plans to relaunch the $160 million growth-stimulating drug.

According to the news service, researchers from Texas Tech University and Kansas State University found that more than 3,800 Zilmax-fed cattle died in 2011 and 2012, with between 40% and 50% of deaths likely attributable to Zilmax. Those numbers run more than tenfold the 285 deaths Merck reported during 6 years of Zilmax sales, Reuters found.

Merck points out that the researchers' findings, published Wednesday in the journal PLOS ONE, were based on observational data. That's not a reliable method, Merck contends. "Using observational analyses where cattle are not randomized and where rigorous scientific procedures are not utilized, is not a respected scientific method to rigorously evaluate the safety and efficacy of any product," the pharma giant told Reuters in a statement.

The researchers did warn that establishing a causal relationship between Zilmax and higher death rates is tricky because of the data's observational nature. On the flip side, as one of the report's authors told Reuters, the lower death rates Merck reported could be flawed by human error. Customers may not have recognized that Zilmax could be causing the animal deaths--and, thus, failed to report them. "It's taken a huge amount of observation to start to piece together some of these side effects, or adverse drug events if you will," he said.

Either way, the study won't reassure the already-hesitant cattle raisers Merck will need on its side as it tests the waters for a Zilmax relaunch. After early reports of hoof loss and pneumonia, industry-leading processors Tyson and Cargill refused to take Zilmax-fed cattle. Now, important meat packers in the U.S. and Canada say they're reluctant to pick the drug up again.

Merck has reportedly been looking to bolster its animal health business, whose sales slumped 1% in 2013. Back in January, the company was said to be in talks with Novartis ($NVS) concerning a $5 billion swap that would have sent Merck's consumer unit to Switzerland in exchange for Novartis' vaccines and animal health divisions. But those talks have since cooled, with Merck shopping around its consumer unit for a potential sale worth as much as $12 billion.

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