PetMD’s medications content was written and reviewed by veterinary professionals to answer your most common questions about how medications function, their side effects, and what species they are prescribed for. This content shouldn’t take the place of advice by your vet.
What Is Fenbendazole for Dogs and Cats?
Fenbendazole is the active ingredient in several common veterinary deworming medications for dogs and cats for the removal of intestinal worms including roundworms, hookworms, whipworms, and tapeworms, and protozoal parasites including Giardia.
Fenbendazole is FDA-approved for use in veterinary medicine to treat a wide variety of worms in horses, cattle, swine and goats. In dogs, it is FDA-approved to treat roundworms, hookworms, whipworms, and tapeworms.
Although fenbendazole is currently not FDA-approved as a veterinary medication in other species such as cats and ferrets, veterinarians can legally prescribe medications for use in other animals in certain circumstances. This is called extra-label or off-label use because this use isn’t described on the drug label.
Fenbendazole is available in oral formulations under the brand names Panacur® and Safe-guard®. Fenbendazole is available over-the-counter as single-use packets, or by prescription from your vet in granule, liquid, chew, and capsule forms.
In certain circumstances, your vet may recommend a compounded formulation of fenbendazole. Compounded medications are prescribed if there’s a specific reason your pet’s health can’t be managed by an FDA-approved drug, such as if your pet has trouble taking pills in capsule form, the dosage strength is not commercially available, or the pet is allergic to an ingredient in the FDA-approved medication.
Compounded medications are not FDA-approved. They are created by either a veterinarian or a licensed pharmacist on an individual basis to best suit a patient’s particular needs. You can learn more about compounded medications here.
Fenbendazole should be used with caution in pets that are hypersensitive to the medication.
Giving fenbendazole with certain medications can result in health risks to your pet, so it is important to discuss your pet’s medications, including vitamins and supplements, and medical conditions with your veterinarian.
It is important to note that fenbendazole does not treat all types of parasites, including the tapeworm spread by fleas. A different type of deworming medication may be necessary, especially if parasites are still present after treatment. Your veterinarian may perform fecal tests to ensure the medication is working and to determine if parasites are still present.
Check with your veterinarian about meat or milk residue requirements if you are using fenbendazole in food animals (cattle, goats, sheep, swine), as they can advise you on how long milk must be discarded and the length of time needed to wait before slaughter.
How Fenbendazole Works in Dogs and Cats
Fenbendazole blocks the ability of worms to produce energy, which ultimately starves and kills the parasite. Immature life stages, such as larvae or eggs, may also be affected in some types of worms.
Fenbendazole Directions for Dogs and Cats
Follow the directions on the drug label or as provided by your veterinarian. Fenbendazole is best absorbed if given with food.
Many puppies are dewormed after weaning at 6, 8, 10, and 12 weeks of age. The nursing mother dog should also be dewormed. Adult dogs may require deworming twice yearly or when parasites are present. Your veterinarian will determine a schedule that is appropriate for your pet.
Missed a Dose?
Speak with your veterinarian about what to do if you forget to give a dose of fenbendazole. Generally, they may instruct you to give it when you remember, or if it is almost time for your pet’s next dose, to skip the missed dose and resume your normal dosing schedule. Do not give extra or double doses.
Possible Side Effects of Fenbendazole in Dogs and Cats
When used as labeled, fenbendazole in dogs and cats is generally well tolerated, and side effects are uncommon.
The following side effects may be seen:
Allergic reaction (anaphylaxis) including hives, facial swelling, lethargy, trouble breathing, or collapse
Seek immediate medical treatment if you suspect your pet may be having an allergic reaction. Contact your veterinarian if your pet is experiencing stomach upset.
Human Side Effects
Fenbendazole is a prescription veterinary medication not intended for use in humans. Wash your hands after handling this medication.
Due to possible side effects, humans should never use medicine dispensed for their pets and pets should not be given any medicine dispensed for a human’s use.
If you accidentally ingest a pet medication, call your physician or the national Poison Control Center hotline at 800-222-1222.
No specific monitoring is required for this medication, but your veterinarian may recommend routine testing depending on your pet’s individual needs, other medications they may be on, and/or the issue that initially caused your pet to be placed on this medication.
Call Your Vet If:
Severe side effects are seen (see above)
Your pet’s condition worsens or does not improve with treatment
You see or suspect an overdose
You have additional questions or concerns about the use of fenbendazole
Fenbendazole Overdose Information in Dogs and Cats
An overdose of fenbendazole in dogs and cats is unlikely to cause toxicity. Large overdoses given over long periods of time may result in a suppressed bone marrow (bone marrow hypoplasia) resulting in abnormally low blood cell numbers.
If you suspect an overdose, contact your veterinarian or an animal poison control center. Consultation fees often apply.
Pet Poison Helpline 855-764-7661
ASPCA Animal Poison Control 888-426-4435
Always confirm storage requirements by reading the prescription label.
Compounded medications should be stored according to the compounding pharmacy’s label.
Store this medication at room temperature at or below 77 F. Do not freeze this medication. Keep the container tightly closed in order to protect from moisture and light.
Keep out of reach of children and pets.
How long does it take for Panacur® to work for a Giardia infection?
Giardia is a microscopic protozoal parasite that can infect the digestive tract and cause diarrhea in animals and humans. Panacur® is one of the medications veterinarians prescribe to treat this infection.
It is important to closely follow the instructions provided by your veterinarian because it is possible for Giardia to spread from pets to humans.
Veterinarians typically prescribe Panacur® for three to five days to treat Giardia, but the length of treatment may vary or even be extended depending on your pet’s response to the medication.
Your veterinarian may also likely recommend a specific bathing program for your pet to prevent reinfection, and recommend testing a fecal sample after finishing the medication to ensure that the treatment was successful.
What kind of worms does Panacur® kill?
Panacur® and other fenbendazole products treat roundworms, hookworms, whipworms, and tapeworms in dogs. Your veterinarian may prescribe Panacur® to treat other types of parasites, including Giardia and lungworms.
How long does Panacur® take to work in cats?
Panacur® and other fenbendazole products are not FDA-approved for use in cats. However, your veterinarian may prescribe Panacur® to treat certain types of parasites. Treatment times vary between parasites. Follow the instructions provided by your veterinarian.
Can I use Panacur® prescribed for horses on my dog?
No. It is important to only use dog medications in dogs and horse medications in horses. Horse medications are usually much more concentrated than dog medications, making overdoses more likely.
No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer.
McKellar Q, Galbraith E, Baxter P. Oral absorption and bioavailability of fenbendazole in the dog and the effect of concurrent ingestion of food. Journal of Veterinary Pharmacology and Therapeutics. 1993;16:189–198.
Dear Veterinarian Letter regarding adverse events associated with extra-label use of fenbendazole in dogs. (December 2023). fda.gov.
Saleh M, Gilley A, Byrnes M, Zajac A. Development and evaluation of a protocol for control of Giardia duodenalis in a colony of group-housed dogs at a veterinary medical college. Journal of the American Veterinary Medical Association. 2016;249(6):644–649.
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