Arthritis treatment in dogs under fire after reports of severe, even fatal side effects

A popular arthritis drug for dogs may be riskier than we knew. This week, the Food and Drug Administration reported several serious adverse reactions and deaths linked to the recently approved drug Librela.

On Monday, the FDA’s Center for Veterinary Medicine issued letter to veterinarians detailing the results of their investigation into Librela. The FDA has identified numerous serious adverse effects associated with its use, including seizures and loss of muscle function; several dogs have also died or been euthanized due to these complications. The agency recommends that the drug’s manufacturer update its label to include these potential side effects, and advises veterinarians and the public to report any adverse events associated with its use.

Librela’s active ingredient, bonevetmab, is a laboratory engineered antibody developed by the company Zoetis. In 2023 FDA approved for the treatment of osteoarthritis in dogs. The drug – delivered by injection once a month – targets and inhibits a protein involved in pain regulation called canine nerve growth factor (NGF). The drug is designed to reduce NGF levels, which tend to be higher in dogs with osteoarthritis. It is the first monoclonal antibody-based drug ever approved for dogs and the second ever approved for pets.

During its approval, some of the most common side effects associated with Librela were certain types of infections (UTIs, bacterial skin infections), rash, vomiting, and weight loss. As is standard for any approved drug, the FDA monitors reports of adverse events related to Librela submitted by patients and physicians. Some dog owners have reported very serious—even fatal—symptoms in their pets after starting Librela.

According to the FDA, there were 3,674 adverse event reports involving Librela as of March 2024. These adverse events are more common in older dogs, which makes sense given that age is a common risk factor for osteoarthritis. The FDA has identified many potentially serious adverse reactions that are not currently listed on the drug’s label as a possible side effect. These include ataxia (poor muscle control), seizures, diarrhea and paralysis. In some cases, dogs die or are euthanized soon after developing these severe events.

In one case, for example, a 10-year-old Great Pyrenees developed ataxia one hour after taking Librela. Within a day, the dog developed incontinence and hind limb lameness, which eventually spread to the dog’s front limbs. Within two days the dog was paralyzed. Four days after taking the medicine, the dog died.

The FDA is careful to note that these adverse events have not yet been definitively linked to Librela. At the same time, the agency rejected the idea raised by Zoetis that the high number of reports related to the drug was simply caused by negative publicity on social media.

“There is no evidence that the reported cases are not genuine Librela-related cases,” the agency wrote in its review from these reports.

Zoetis issued a statement after the FDA letter. The company criticized some media outlets for allegedly mischaracterizing the FDA’s communication as a “warning” rather than an “informational update” intended to educate veterinarians and the public. The company also claims, based on data from the European Union, that any identified adverse event associated with Librela is likely to be rare.

“We remain confident in the safety and effectiveness of Librela and are committed to supporting veterinarians and pet owners to help dogs live with less pain and greater mobility,” the company said in a statement.

More time and research will be needed to confirm these serious side effects. But in the meantime, the FDA has recommended that Zoetis update its Librela labeling to mention these potential adverse events (the Center for Veterinary Medicine itself cannot mandate safety-related labeling changes).

While Zoetis stands by its drug, it said it is discussing possible labeling changes with the FDA. The FDA also advises dog owners and veterinarians to continue to report adverse events related to the use of the drug.