A popular arthritis drug for dogs may be riskier than we knew. This week, the Food and Drug Administration reported the emergence of several serious adverse effects and deaths associated with the recently approved medication Librela.
On Monday, the FDA’s Center for Veterinary Medicine issued a letter to veterinarians detailing the results of their investigation into Librela. The FDA identified numerous serious adverse effects linked to its use, including seizures and a loss of muscle function; several dogs also reportedly died or were euthanized due to these complications. The agency is recommending that the drug’s maker update its labeling to include these potential side effects, and is advising vets and the public to report any adverse events linked to its use.
Librela’s active ingredient, bedinvetmab, is a lab-made antibody developed by the company Zoetis. In 2023, the FDA approved it to treat osteoarthritis in dogs. The drug—delivered via injection once a month—targets and inhibits a protein involved in pain regulation called canine nerve growth factor (NGF). The drug is designed to tamp down levels of NGF, which tend to be higher in dogs with osteoarthritis. It’s the first monoclonal antibody-based drug ever approved in dogs, and the second ever approved for pets.
At the time of its approval, some of the most common side effects associated with Librela were certain kinds of infection (UTIs, bacterial skin infections), rash, vomiting, and weight loss. As is standard with every approved drug, the FDA has been monitoring reports of adverse events associated with Librela filed to it by patients and doctors. And some dog owners have reported very serious—even fatal—symptoms in their pets after they started taking Librela.
According to the FDA, there have been 3,674 adverse event reports involving Librela, as of March 2024. These adverse events have been more common among older dogs, which makes sense given that age is a common risk factor of osteoarthritis. The FDA identified many potentially serious adverse events currently not included in the drug’s labeling as a possible side-effect. These include ataxia (poor muscle control), seizures, diarrhea, and paralysis. In some cases, dogs died or were euthanized soon after they developed these severe events.
In one case report, for instance, a 10-year-old Great Pyrenees developed ataxia an hour after taking Librela. Within a day, the dog developed incontinence and hindlimb lameness, which eventually spread to the dog’s forelimbs. Within two days, the dog had become paralyzed. Four days after taking the drug, the dog died.
The FDA is careful to note that these adverse events have not been conclusively tied to Librela as of yet. At the same time, the agency dismissed the notion, brought up by Zoetis, that the large number of reports tied to the drug was simply caused by negative publicity on social media.
“There is no evidence that the cases being reported are not true cases associated with Librela,” the agency wrote in its review of these reports.
Zoetis issued a statement following the FDA’s letter. The company criticized some media coverage for purportedly mischaracterizing the FDA’s communication as a “warning,” rather than an “informational update” meant to educate veterinarians and the public. The company also argued, based on data from the European Union, that any identified adverse event associated with Librela is likely to be rare.
“We remain confident in Librela’s safety and effectiveness and are committed to supporting veterinarians and pet owners in helping dogs live with less pain and greater mobility,” the company said in its statement.
It will take more time and research to confirm these serious side effects. But in the meantime, the FDA has recommended that Zoetis update its labeling of Librela to mention these potential adverse events (the Center for Veterinary Medicine itself cannot mandate safety-related labeling changes).
While Zoetis is standing by its drug, it did state it was discussing possible labeling changes with the FDA. The FDA is also advising dog owners and vets to continue reporting adverse events associated with the drug’s use.
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