Drug approved to treat dogs for chemotherapy-related diarrhea

Food and Drug Administration officials granted conditional approval in mid-December for the oral prescription drug Canalevia-CA1, the first drug with an approval to treat chemotherapy-induced diarrhea in dogs. The delayed-release tablets contain crofelemer, which is also used to treat diarrhea in people who are undergoing antiretroviral therapy for HIV/AIDS.

Dr. Steven M. Solomon, director of the FDA Center for Veterinary Medicine, said in a Dec. 21, 2021, announcement that diarrhea is a common side effect of chemotherapy in dogs, and it can be so severe that treatment must be halted.

“Chemotherapy drugs often have potential side effects, but, unlike in human medicine where patients may be willing to tolerate some discomfort in exchange for a potential cure, the primary purpose of cancer treatment in dogs and other pets is to extend survival without sacrificing quality of life and comfort,” Dr. Solomon said in the announcement. “This new medication provides veterinarians and dog owners with another tool to help control the side effects of chemotherapy for dogs undergoing such treatment.”

Labrador retriever in veterinary clinic receiving an infusion

Dr. Cheryl London is a veterinary oncologist, a research professor, and associate dean of research and graduate education at the Cummings School of Veterinary Medicine at Tufts University, and her work is unconnected with Canalevia-CA1. She said few other treatments are available for dogs with chemotherapy-related diarrhea, and none are very successful.

Those include probiotics, over-the-counter products, and the antimicrobial metronidazole, and administering the latter also increases the risk of selecting for antimicrobial resistance, Dr. London said.

Canalevia-CA1 gained the conditional approval through a marketing pathway for minor uses in major species, a designation that allows drug companies to sell a drug for a condition affecting a small portion of an animal population while continuing to gather evidence of its effectiveness. A company needs to demonstrate the drug is safe and show it is reasonable to expect the drug will be effective prior to conditional approval, and the drug sponsor needs to gain full approval within five years to keep selling the drug.

FDA officials said a study of 24 dogs provided a reasonable expectation of effectiveness. A dog was considered a treatment success if its diarrhea resolved and didn’t recur during the three-day study. The agency announcement states that nine of the 12 dogs in the treatment group no longer had diarrhea, in comparison with three of the 12 dogs in the control group. In laboratory and field studies, the most common side effects were abnormal feces, decreased appetite and activity, and vomiting, the announcement states.

A version of this article appears in the Feb. 1, 2022, print issue of JAVMA.