A popular drug for dogs with arthritis may be associated with a variety of potentially severe neurological effects, including seizures and a loss of muscle control, according to a recent review by the U.S. Food and Drug Administration, which approved the drug last year. In some cases, dogs have died or have been euthanized after developing these symptoms, the agency noted.
The drug, called Librela, is an injection of monoclonal antibodies that is approved for arthritis-related pain in dogs. Its label lists mostly mild side effects, such as urinary tract and skin infections.
But since the drug became widely available, some pet owners have reported that their dogs became seriously ill, lost the ability to walk or stand or even died shortly after receiving the drug.
The F.D.A.’s analysis, which is based on more than 3,600 adverse-event reports submitted to the agency and the drug manufacturer, does not prove that Librela caused these problems or estimate how frequently they might occur.
But such reviews can help regulators identify potential side effects that smaller clinical trials may have missed. The F.D.A. has alerted veterinarians to the adverse events that may be associated with Librela and recommended that the drug’s label be updated to include them.
Zoetis, the company that makes Librela, said that more than 21 million doses of the drug had been distributed globally and that side effects were rare. “We at Zoetis — and I personally — stand 100 percent behind Librela as safe and effective,” said Dr. Richard Goldstein, the company’s chief medical officer.
It is not uncommon for a drug’s label to be revised after approval, and Zoetis is “working actively” with the agency on that process, Dr. Goldstein said.
Librela contains monoclonal antibodies that block the activity of nerve growth factor, a protein that plays a key role in the transmission of pain signals inside the body. In some dogs, it can have enormous benefits, veterinarians say, significantly improving their mobility and quality of life.
“This is a drug that has a place, and I think an important place,” said Dr. Rory Todhunter, a veterinarian who directs the Richard P. Riney Canine Health Center at Cornell University. “I just think owners need to be warned that there are risks involved.”
The F.D.A.’s review and its recommendation for updated labeling came as vindication to pet owners who say that their dogs have been seriously harmed by Librela and who have been trying to draw attention to the issue.
“To tell you that we’re thrilled is just an understatement,” said Lita Dwight, a co-executive director of Paws Over Profits, a nonprofit group that aims to raise awareness about the drug’s potential side effects.
Ms. Dwight co-founded the organization after her miniature dachshund Lacey became seriously ill and then died shortly after receiving her first dose of Librela. She had not been warned about the possibility of severe side effects, she said.
“As a pet parent, I want informed consent,” Ms. Dwight said. “I want the doctor to know what the side effects are, to give me the choice of whether or not I want to take on that risk.”
The drug, which was authorized in Europe in 2020, was approved in the United States in May 2023. Reports of serious side effects soon began to spread online, in places including large Facebook groups, where some dog owners shared success stories and others relayed tragic ones.
Because Librela is generally given to older dogs, which may have a variety of underlying health issues, it has been difficult to determine whether the drug itself has been the cause of the severe symptoms reported in some dogs.
“A lot of old dogs have arthritis plus neurologic disease, and sometimes it’s hard to tell a difference between the two,” Dr. Todhunter said.
Still, the F.D.A. identified a number of side effects that were reported more often in dogs given Librela than in those taking other drugs for arthritis pain. Those included a loss of muscle coordination and control, which was the most common adverse event reported, as well as muscle weakness, lameness, paralysis and an inability to stand.
The F.D.A. review dismissed the possibility that discussions of Librela on social media had caused an overreporting of adverse events. “There is no evidence that the cases being reported are not true cases associated with Librela,” the agency noted.
More research is required to identify the exact causes of and risk factors for potential side effects, said Dr. Todhunter, who noted that the drug might not be a good choice for dogs that have underlying neurological conditions.
