Fenbendazole is an anthelmintic medication that has been in use as a parasiticide for over 50 years. It belongs to the benzimidazole (I coined this group Benz) family of anti-parasitic medications and is very broad spectrum. It is used in dogs to treat and prevent intestinal parasites such as roundworms, hookworms and whipworms, and to protect against the Taenia species of tapeworm, as well as giardia and lungworm in puppies. It is also widely used in livestock such as cattle and horses.
Fenbendazole inhibits the polymerization of microtubules in helminths by binding to them and disrupting their balance (1-4). It is an effective drug against many types of parasites in mammals, but has limited effectiveness in helminthes that are resistant to other anthelmintics. Its utility in veterinary medicine stems from its high permeability to tissues of the digestive tract, which allows it to reach its target cells in the large intestine, and its moderate rate of absorption.
In addition to its utility as an anthelmintic, the drug has been shown to exhibit significant radiosensitization in cell cultures (5-10). However, there has been no human or animal cancer trial data to support these claims. Recently, videos promoting the deworming medication as a cure for alleged small-cell lung cancer have been reposted on social media such as TikTok and Facebook and have been met with criticism from experts in veterinary oncology.
The authors of a recent study on fenbendazole and its effect on radiation response reported no change in the growth rates of unirradiated or irradiated tumors. They randomized mice with tumors of varying volumes at a mean value of 100 mm3 into groups that either received no treatment, three daily i.p. injections of fenbendazole, or the same treatment plus 10 Gy of x-rays. Tumors were measured at the time of stratification to determine their volume and then every two weeks. The growth of each group was compared to the control group using a geometric mean (+/- SEM) with 7-8 mice per group.
Like many other anthelmintics, fenbendazole is well-tolerated by healthy adult dogs with minimal side effects. Dogs with liver or kidney disease, however, are at higher risk of developing adverse reactions to this medication. If your dog shows any of the signs of an allergic reaction, including facial swelling or hives, contact your veterinarian immediately. Also, tell your veterinarian if your dog is taking any other medication, including vitamins, supplements or herbal therapies, so that they can monitor for potential interactions. fenbendazole capsules