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Stomach upsets and digestive issues in felines is often caused by the infestation of gastrointestinal parasites. The use of fenbendazole is often employed by vets to combat this condition. However, this use of fenbendazole is strictly off-label since the drug was not initially intended for the treatment of parasite infestation in cats.

Fenbendazole is an anthelmintic, which is a type of drug that kills internal parasites by preventing the absorption of nutrients in the host’s body, greatly hindering the parasite’s ability to survive in the host’s body. However, this drug only affects the parasites and not the eggs it lays. Fenbendazole can be used to fight several different parasites that may infest cats such as threadworms, roundworms, some forms of tapeworms, hookworms and whipworms. Fenbendazole is also known to work against some parasites that infest the lungs and bronchial tree of a cat. There are no known human formulations of this drug as it is meant for animals only. 

It is also used as a broad-spectrum deworming drug if a pet has chronic diarrhea and the root of it cannot be located. It can destroy the parasites that may cause the condition even if they have not been detected in tests.

Cat Fenbendazole

Fenbendazole Dosage & Administration

Even though Fenbendazole is an over-the-counter medication, it should never be administered without the advice of a veterinarian. Since it is not too effective as a standalone dose, fenbendazole should be administered to the affected cat consecutively for days. It can be administered orally as it is available in the concentration of 222mg per gram in the form of tablets or a suspension and 100mg per gram pastes. Fenbendazole should be administered with food to reduce the chances of gastrointestinal upset. The duration of the course of treatment is dependent on the condition of the cat that is receiving treatment.

If a dose is missed, the cat should not be given two doses at once, instead, the course should be continued for an extra day to compensate for the missed dose.  It is to be noted that if the drug has done its job after a few doses and the cat seems to be in better shape, the drug should not be ceased immediately, the full course of the treatment should always be completed, this prevents the survival of any parasites in the cat’s system. Also, after the course is completed, the cat should be retested for gastrointestinal parasites to check whether a second course of the drug is needed. As a general rule of thumb, the dosage most commonly prescribed to cats.

Cat in box

Dosing Guidelines

23mg or 0.1ml for 1lbs,

46mg or 0.5ml for 2lbs,

69mg or 0.7ml for 3lbs,

92mg or 1ml for 4lbs,

115mg or 1.2ml for 5lbs,

138mg or 1.4ml for 6lbs

161mg or 1.6ml for 7lbs,

184mg or 1.8ml for 8lbs,

207mg or 2.1ml for 9lbs

230mg or 2.3ml for 10lbs

253mg or 2.5ml for 11lbs

276mg or 2.8ml for 12lbs

299mg or 3.0ml for 13lbs

322mg or 3.2ml for 14lbs

345mg or 3.5ml for 15lbs

368mg or 3,7ml for 16lbs

391mg or 3.9ml for 17lbs

414mg or 4.1ml for 18lbs

437mg or 4.4ml for 19lbs

460mg or 4.6ml for 20lbs

Since Fenbendazole tablets are only available in the 222mg form, they must be divided into the correct dose if it is lower than 222mg. The best way to feed the drug to a cat is by crushing it into the cat’s food. This allows for easy ingestion and will save the owner a lot of effort when it comes to getting their cat to eat the tablet. The typical duration of the course of treatment for Fenbendazole is around 3-5 days.

Safety and possible side effects

Fenbendazole is not approved by the USFDA for use in cats, however, it is still used as an off-label drug upon the advice of vets. It is generally considered to be a safe drug to use to treat cats, though cats that are allergic to it or are known to have hypersensitivity should not be exposed to fenbendazole. Healthy cats, when compared to dogs, can tolerate a dose that is up to 3 times larger. However, fenbendazole can have some side effects in some animals. Though rare, animals that have been treated using this drug may vomit or salivate excessively after the drug is administered.

The chemicals released by the dying or dead parasites may also cause an allergic reaction within the cat’s body. This is mostly only seen in very high doses. Fenbendazole may also cause cats to lose their appetite and cause lethargy. The withdrawal time of fenbendazole is 3-5 days but its effects may last longer in pets with renal or liver problems. Though fenbendazole is safe when used to treat most cats, it should never be used in cats that are younger than 6 weeks old.

cat fenbendazole dosage

Fenbendazole should not be used in animals that suffer from some other sickness that may interfere with the drug’s action. It is advisable to inform the veterinarian about any vitamins, supplements, herbal therapy or homeopathic treatments that the pet is receiving. Fenbendazole is also safe to use in pregnant or lactating cats.

Fenbendazole is known to react with. Praziquantel, another drug used to treat worms and parasites in a cat, and Dexamethasone, a glucocorticoid that is used to treat a lot of illnesses, ranging from inflammation to autoimmune diseases. Fenbendazole also seems to react with salicylanilides like niclosamide which are also used for deworming. Although this drug combination is very harmful for cattle and sheep, it doesn’t affect felines negatively at all. Miscarriages have been observed to happen in cattle after both these drugs were used together.

Other Uses of Fenbendazole

Fenbendazole can also be used as a dewormer in cattle. It has a low degree of toxicity and does not cause any adverse effects. It is efficient at attacking the parasites that form within the animal’s gastrointestinal tract by interrupting their cellular transport and also affecting their metabolism.

This causes the energy reserves of the parasite to empty really quickly, and it also hinders their excretory and protective factors. Fenbendazole can be given to cattle at a dosage of 2g/kg without any adverse effects. As seen when used in cats, retreatment may be needed in cattle after the first course of treatment is over.

Fenbendazole is also very effective at removing most gastrointestinal parasites that infect canines. Fenbendazole is very safe for dogs as even 100 times the recommended dose of 25mg/lb can be tolerated by dogs without the manifestation of any side effects. It is also safe for use in pregnant and lactating dogs. An accidental overdose, which is already very unlikely, causes vomiting and diarrhea. Fenbendazole should never be given to puppies that are under six weeks old.

Dogs that are hypersensitive or are simply allergic to fenbendazole should also never be exposed to the drug as it may cause an allergic reaction.

Scientists have found that fenbendazole can be used against cancer as well. The researchers working at the National Centre for Human Genome Studies and Research of Punjab University have reported that fenbendazole may have potential as an anti-cancer agent. The drug’s effectiveness was first used to treat human lung cancer cells. It was found that the drug caused the slowing of the cell death-inducing activity. Fenbendazole was also used in mice, who were fed the drug every alternate day for 12 days.

After the 12th day, the tumors in the mice were measured and weighed. The researchers found a reduction in the size and weight of the tumors. It was also found that fenbendazole inhibited the uptake of glucose in the bloodstream. Since fenbendazole is very safe and has very low toxicity, it is also tolerated very well by most species, hence, making it a great option as an experimental drug which can be a good candidate for the development of anticancer medicine.


As a broad-spectrum anthelmintic, Fenbendazole is very effective. It is an excellent dewormer and is very safe for most animals. It has shown no known signs of toxicity in any animal even though it is highly toxic to birds. Its effectiveness against such a wide range of parasites is another factor why fenbendazole should be used ahead of other anthelmintics.

Cats show very good tolerance towards the drug, thereby reducing the chance of an accidental overdose. However, it is to be noted that hypersensitive or allergic cats will still have allergic reactions to the drug. The drug is also an OTC medicine, though it should only be used upon the advice of a vet.

The list of positives for fenbendazole includes Its effectiveness, its safety, and its easy availability. All in all, it is safe to say that fenbendazole is one of the premier options when it comes to dewormers and is easy to recommend to all.



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