Safe-Guard (fenbendazole) Equine dewormer from Merck Animal Health is a 10% fenbendazole paste used for the control of large and small strongyles, pinworms and ascarids in horses. The easy-to-use oral syringe contains 25 grams of paste and treats up to 1,100 pounds of body weight. To ensure palatability and decrease chance of waste, this dewormer is flavored with an apple-cinnamon taste. It may be used for horses and ponies, including pregnant mares, breeding stallions and foals. This equine dewormer can be used in a power dose (double dose) to effectively and safely kill ascarids in young horses and late stage strongyles.