Merck & Co.’s COVID-19 antivirals are getting a new lease of life in post-pandemic China, as cat owners seize on them as antidotes to a life-threatening disease caused by a coronavirus that infects their feline companions.

People are feeding their furry friends Merck’s Lagevrio to treat feline infectious peritonitis, a fatal disease that until recently had no readily available treatment, local media outlet Jiemian reported this week.

The move has been a hot topic on social media, with tens of thousands of cat lovers taking to Xiaohongshu, China’s version of Instagram, to discuss how the drugs saved their pets, along with money on expensive veterinary bills.

“COVID-19 drugs for humans saved my cat’s life,” one user wrote on Xiaohongshu. “I share the notes here to teach more people to save their furry babies and reduce the pain suffered by cats.”

In addition to the foreign antivirals, some pet owners also have opted for similar but cheaper COVID medicines developed by homegrown companies including Henan Genuine Biotech Co., Simcere Pharmaceutical Group Ltd. and Shanghai Junshi Biosciences Co.

Merck didn’t immediately reply to Bloomberg’s emailed request for comments.

Chinese pet owner’s use of human COVID drugs on animals is in stark contrast to the early days of the pandemic, when the use by people of ivermectin in the U.S. — a drug to treat parasitic worms in animals — prompted the U.S. Food and Drug Administration to post the words of caution: “You are not a horse. You are not a cow. Stop it.”

Feline infectious peritonitis is a viral disease caused by the so-called feline coronavirus that infects white blood cells before spreading throughout a cat’s body, causing inflammatory reactions. The disease is fatal without treatment. FIP is unique to cats, and not contagious to people, dogs, or other animals.

No specific treatment was available until recently. Some antiviral drugs have proved to be effective, but they aren’t widely accessible. The most popular, GS-441524, developed by Gilead Sciences, hasn’t been approved by the FDA, and cat owners often seek the drug through black market sources.

Chinese cat owners have to rely on informal networks to purchase GS-441524, which often cost tens of thousands of yuan. On Chinese social media, many people complain the drug is too expensive and that many black market sellers gave them a fake version.

Human COVID antivirals are much more affordable, they said. A 40-pill bottle of Lagevrio, for example, costs about 1,725 yuan (US$236) online, and is enough to treat more than one cat. In addition to the drugs, Chinese cat owners also feed their pets nutritional supplements developed for humans, because they are cheaper than veterinary drugs.

“I don’t understand why medicines for pets are so expensive,” wrote one Xiaohongshu user. “You just need to adjust the dosage of human medicines if you are going to use them on cats.”