What killed their pets? Owners blame meds, but vets aren’t sure

Phil and Anne Jordan’s 12-year-old rescue dog Daisy. PHOTO: ANNE JORDAN
Phil and Anne Jordan’s 12-year-old rescue dog Daisy. PHOTO: ANNE JORDAN


Health authorities are reviewing thousands of reports of side effects. Maker Zoetis says the side effects are rare and its arthritis drugs are safe.

Phil Jordan’s 12-year-old rescue dog Daisy struggled with a stiff right rear hip. When the new arthritis drug Librela became available, Jordan and his wife decided to try it.

About two weeks after the first injection in January, however, Daisy wobbled on both hips and limped. A week after her second dose, the dog couldn’t walk, became lethargic and lost her appetite. She gained back some mobility, but her kidney function plunged. In March, the Jordan family euthanized their dog.

“There’s a tremendous amount of guilt that we feel," said Jordan, an economist from Wrentham, Mass.

Librela and a similar treatment for cats were the first antibody drugs for pets approved by the Food and Drug Administration. They promised to relieve a painful arthritis in animals and become an important new franchise for maker Zoetis, the world’s largest animal-health company by sales.

Now they are at the center of a medical mystery. Some pet owners blame the drugs for sickening their animals, some of which then died. Was it the drugs? Were they being used the wrong way? Or were other illnesses afflicting the pets at fault?

Health regulators in the U.S. and Europe—which have received thousands of reports of side effects—are conducting reviews. Some veterinarians are refining use of Librela and the cat therapy Solensia. Wall Street analysts have asked Zoetis about the pet owners’ complaints.

Zoetis says the medicines are safe, with reports of side effects representing well less than 1% of the more than 18 million shots of both drugs combined administered to date in the U.S. and abroad. Many veterinarians and pet owners have also reported success with the drugs. Neither the company nor arthritis and animal-health researchers know of a link between the drugs and the reported side effects.

“In both human health, animal health, there’s no drug that’s risk-free. When those reports come in, of course we take them very seriously," said Rob Polzer, Zoetis’s research-and-development chief.

Animal-health researchers and veterinarians say more study is needed to determine whether the drug might be at fault, possibly by exacerbating an underlying nerve condition or other diseases. The problem could also be older animals’ other medical issues.

Veterinarians may want to make sure they are giving the drugs only to pets matching the profile of the animals studied during testing to reduce the risks, the animal experts say.

Veterinarians have given a drug “without doing complete work-ups and examinations under the guise that it can’t do any harm when, in fact, it can do harm," said Dr. Darryl Millis, a professor of orthopedic surgery at the University of Tennessee College of Veterinary Medicine.

Librela and Solensia went on sale in the U.S. in 2023 and 2022, respectively, aiming for a piece of the $45 billion-plus animal-health market.

Librela and Solensia had $124 million in global sales last quarter. Zoetis, which had $8.5 billion in revenue last year, has described the franchise to investors as its “Next Big Opportunity" and projected yearly sales could surpass $1 billion.

The drugs belong to a class targeting a protein, called nerve growth factor, that plays a key role in signaling pain. Researchers have found the protein at elevated levels in animals with arthritis. After blocking it, the pets would feel less pain and enjoy a better quality of life, according to Zoetis.

Pharmaceutical companies had been working on such drugs for use in people, before dropping the experimental medicines due to safety concerns.

Zoetis says it developed Librela and Solensia specifically for dogs and cats—they aren’t the same as the drugs that had been tested in people—and researchers didn’t find the same safety issues that had doomed the human treatments.

Common side effects reported during testing of Librela included urinary tract infections, lethargy and increased blood urea nitrogen, a sign of problems with kidney function. For Solensia, the most common side effects were vomiting and diarrhea.

Cassie Stover’s 16-year-old cat Max appeared lethargic, wobbled his head and was barely able to move after getting a Solensia injection for suspected arthritis in December, she said. The issues lasted for two months. The cat’s kidneys eventually failed. He died a day before he was scheduled to be euthanized in February, said Stover, 35, of O’Fallon, Mo.

The FDA received more than 3,800 reports of side effects concerning the drugs through the end of last year. The European Medicines Agency has received more than 12,300 reports of side effects involving Librela and more than 7,700 for Solensia since 2021, when the drugs went on sale in Europe. The figures include reports from the U.S. and other countries outside of the European Union.

Pamela Boyd, a 34-year-old part-time veterinary technician in San Marcos, Texas, said her dog struggled to walk, became weak and anxious and had a fever for three days after his first Librela injection in January.

A joint tap after the dog received the injection showed the animal had an immune response, called immune-mediated polyarthritis, that makes it difficult to walk and causes joint swelling.

“It was not good at all," said Boyd, who put down her dog Soren last week. “Nothing I’ve ever seen from him before." Boyd started an online petition to recall Librela for further testing that has more than 3,800 signatures.

Dr. Leilani Alvarez, senior veterinarian at the Schwarzman Animal Medical Center in New York City, said many dogs that she has given Librela to have improved significantly, while others showed side effects. One dog with a neurological condition lost energy and was less eager to move, while another couldn’t walk. Both dogs improved after stopping injections. She reported the events to Zoetis.

Meanwhile, Alvarez said she wouldn’t give Librela to dogs with conditions like neurological issues, cancer, immune diseases or kidney problems.

Dr. Duncan Lascelles, a professor of translational pain research and management at North Carolina State University’s College of Veterinary Medicine who helped Zoetis design Solensia studies, recommends prescribing the drug to dogs matching the criteria used in the trial. The trials didn’t include dogs with neurological conditions or lameness unrelated to osteoarthritis.

“Sometimes with the latest thing that’s new and shiny everyone wants it to be this perfect therapeutic in all situations. That’s just not going to happen," Lascelles said. “I don’t know what cases they’re not right for. That’s something we learn over time."

Coulter Jones contributed to this article.

Write to Jennifer Calfas at jennifer.calfas@wsj.com

What Killed Their Pets? Owners Blame Meds, but Vets Aren’t Sure
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What Killed Their Pets? Owners Blame Meds, but Vets Aren’t Sure
What Killed Their Pets? Owners Blame Meds, but Vets Aren’t Sure
View Full Image
What Killed Their Pets? Owners Blame Meds, but Vets Aren’t Sure
What Killed Their Pets? Owners Blame Meds, but Vets Aren’t Sure
View Full Image
What Killed Their Pets? Owners Blame Meds, but Vets Aren’t Sure
What Killed Their Pets? Owners Blame Meds, but Vets Aren’t Sure
View Full Image
What Killed Their Pets? Owners Blame Meds, but Vets Aren’t Sure
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