Your Complete Guide to Canine Deworming Using Fenbendazole for Dogs
Dogs are prone to getting intestinal parasites partly because they love hanging around and playing outdoors. You’ve probably heard your veterinarian tell you that your beloved fur baby has worms at some point in his life!
Worm infestations might seem gross, but they are common and treatable in dogs. There are lots of deworming agents available for dog use, and fenbendazole is among the most commonly prescribed drugs. What is this medication and how does it eliminate parasites from your dog’s body? We’ll find that out plus more information about fenbendazole for dogs in this article.
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- What is Fenbendazole?
- How Does Fenbendazole Work in Dogs?
- What Does Fenbendazole Treat?
- Fenbendazole Dosage Recommendations for Common Parasitic Worms
- Fenbendazole Recommended Dosage for Lungworms
- Suggested Dosage for Giardia in Dogs
- A Quick Note on Dosage Recommendations of Fenbendazole for Dogs
- Potential Adverse Effects of Fenbendazole in Dogs
- Precautions in Giving Fenbendazole to Dogs
- Drug Interactions with Fenbendazole
- How to Care for a Dog Taking Fenbendazole
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What is Fenbendazole?
Fenbendazole is an oral Anthelmintic drug used to eradicate worms and parasites from the body. More specifically, it is classed as a broad-spectrum benzimidazole anthelmintic that can effectively remove hookworms, roundworms, whipworms, and Taenia tapeworms in dogs. This powerful drug is also used in cats, horses, rabbits, seals, cattle, sheep, and even fishes!
The drug is used off-label in the United States to treat Giardia infections and lungworms in dogs. However, European countries approve fenbendazole as a treatment for Giardiasis in dogs.
Panacur is the common brand name of Fenbendazole. The drug comes in liquid, paste, and suspension granule forms which can all be kept under room temperature. Injectables are also available, although oral forms are most commonly prescribed and used. Panacur is used to kill worms on dogs living in shelters.
How Does Fenbendazole Work in Dogs?
Fenbendazole works by disrupting the parasite’s cell division. It binds and interacts with the worms’ microtubules, structures that facilitate several cellular processes in parasites. Fenbendazole binds to the beta-tubulin protein found inside the microtubules, inhibiting its formation and disrupting cell division. The parasites affected by fenbendazole then get starved, cease to multiply, and finally die.
Fenbendazole doesn’t disrupt the animals’ own cells and beta-tubulin. It is highly targeted to affect only the parasites’ cells. This unique property makes the drug very safe not just in dogs, but in many other animals as well.
Fenbendazole is also safe for pregnant and lactating dogs. It’s often administered during pregnancy to reduce the risk of transmitting roundworms and hookworms from the mother dog to her puppies.
Another thing that makes fenbendazole a highly-effective antiparasitic drug is its limited absorption in the body. The medication often stays inside the intestinal tract where the parasites are mostly concentrated. This allows fenbendazole to directly work against the worms infesting the dog right away.
Fenbendazole is most effective against nematodes, but it can also work on certain cestodes such as the Taenia tapeworm. Unfortunately, the drug cannot treat Dipylidium caninum which is the most common type of tapeworm seen in dogs.
Febantel is another anthelmintic medication given to dogs. This drug is metabolized into fenbendazole inside the dog’s body.
What Does Fenbendazole Treat?
Now, let’s have a quick overview of the parasitic worms that fenbendazole can treat:
Hookworms
Hookworms are blood-sucking parasites that attach themselves to the dog’s intestinal walls. The term “hookworm” was coined due to the hook-like structure of their mouthparts. This structure is what they use to cling to the intestinal walls and feed off blood and nutrition from it.
Hookworm infection is especially serious because internal blood loss often comes with it. Young puppies, immunocompromised dogs, and older dogs who get infected with hookworms may suffer dire consequences if blood transfusion is not given promptly.
The most common hookworm species affecting dogs include Ancylostoma caninum, Ancylostoma braziliense, and Uncinaria stenocephala. However, note that fenbendazole is typically effective against A. caninum and U. stenocephala only.
Roundworms
Roundworms are spaghetti-like parasites that stay on the intestines and live off the dog’s partly digested food. They are also known as nematodes or ascarids.
Roundworms are unique in that they can be passed on to puppies from their mother even before they are born. The puppies may also acquire the parasites by drinking milk from the mother dog. Older dogs may get the worms from the environment, especially in soil and water contaminated by other dog’s feces.
Typical roundworm species that infest dogs are Toxocara canis and Toxocara leonina.
Whipworms
Whipworms are small parasites that reside in the dog’s cecum, an area of the dog’s intestinal tract where the small intestines meet the large intestines. They also migrate and stay in the large intestine. Whipworms are named for their characteristic structure with a thicker anterior end and a narrower, longer, and whip-like tail end.
Dogs get whipworms by ingesting stool-contaminated water, food, or soil. Stool swallowing or coprophagia [1] is also a common culprit – your dog may get it by consuming other animals’ stool contaminated with whipworm eggs.
Trichuris vulpis is the whipworm species that often affects dogs. Now, whipworms burrow their heads into the large intestine’s mucosal surface, then suck the blood and water from there to thrive.
Whipworm infection is often suspected when a dog experiences bloody diarrhea. Symptoms may only show up when there is a large number of whipworms embedding themselves inside the large intestine.
Lungworms
Lungworms are another type of parasite that can infect dogs. The worms are scientifically known as Oslerus olseri and are classed as a nematode parasite and a tracheal worm. Other lungworm species that may infect dogs include Eucoleus aerophilus (formerly known as Capillaria aerophila), Eucoleus boehmi, Crenostoma vulpis, and Filaroides hirthi.
Lungworms reside in different areas of the respiratory tract, depending on the species:
- Oslerus olseri, Eucoleus aerophilus, and Crenostoma vulpis – On the trachea and bronchi
- Filaroides hirthi – On the lungs
- Eucoleus boehmi – On the nasal cavity
Adult worms cause respiratory tract irritation which leads to symptoms such as dry cough, wheezing, frequent sneezing, and difficulty in breathing especially when inhaling. Lungworms may be fatal if not diagnosed and treated promptly.
Tapeworms
Tapeworms are parasites that have a segmented and flat appearance, resembling a tape. They belong to the cestode parasite family. Tapeworms attach to the small intestine’s walls and feed off the blood and nutrients from the food inside the intestines.
There are many types of dog tapeworms. Dipylidium caninum is the most common, but Taenia species may also infect dogs. New tapeworm types are emerging and have infected some dogs, such as the Echinococcus multilocularis that was originally from foxes and coyotes.
Currently, Taenia pisiformis is the only tapeworm species that is susceptible to fenbendazole.
Giardia
Technically, Giardia is not a worm. It’s a microscopic intestinal parasite that can infect both dogs and humans alike. Dogs may contract Giardia by swallowing infective cysts from soil and water contaminated with feces.
Giardiasis in dogs may produce chronic diarrhea, pale and fatty stools, and weight loss. Once a diagnosis is confirmed, fenbendazole may be safely given to dogs for less than a week.
Fenbendazole Dosage Recommendations for Common Parasitic Worms
According to the Merck Veterinary Manual, the generally recommended dose for fenbendazole is 50 mg/kg of body weight, given orally for at least 3 days. This dosage is approved in the United States.
Meanwhile, fenbendazole dosage approved in the United Kingdom is 50-100 mg/kg of body weight, given orally for at least 3 days. This dose is relevantly higher than that approved in the USA.
Both dosing suggestions are effective against a range of parasite species including the following:
- T. canis and T. leonina (roundworms)
- A. caninum and U. stenocephala (hookworms)
- Trichuris vulpis (whipworms)
- Taenia pisiformis (tapeworms)
However, veterinarians may prescribe fenbendazole as low as 20-50 mg/kg of body weight, especially if the dog exhibits mild symptoms or has fewer worms in his body. Treatment length may range from 2-5 days and may extend further for more severe infestations.
Fenbendazole is typically used to kill adult-stage parasites, so expect other deworming agents (as single medications or combinations) to be prescribed for your dog especially if he has several worms inside his body.
Fenbendazole Recommended Dosage for Lungworms
Fenbendazole has been successfully used for the treatment of lungworms in dogs. A case report on an 8-month old Labrador retriever infected with C. vulpis used fenbendazole 50 mg/kg given orally every 24 hours for three days. Meanwhile, another case report on Prince Edward Island dogs also infected with C. vulpis lungworm species showed improvement after they were given fenbendazole 50mg/kg, orally given every 24 hours for 3-7 days.
Suggested Dosage for Giardia in Dogs
There is no specific drug used for treating Giardia in dogs. However, veterinarians find success in using fenbendazole to remove Giardia cysts in dog feces. The recommended fenbendazole dosage for giardiasis is 50 mg/kg of body weight, given orally once a day for 5-10 days.
Some veterinarians opt to give a combination drug containing praziquantel, pyrantel, and febantel. This medication can eliminate Giardia cysts after 3 days of continued use. Note that febantel is metabolized into fenbendazole, hence, we included this option here.
A Quick Note on Dosage Recommendations of Fenbendazole for Dogs
All these dosages we presented above are general recommendations only. Your veterinarian will determine the best dosage and treatment length depending on your dog’s breed, weight, type of parasite infection, the extent of infestation, symptoms, medical history, and other related factors.
Always follow your veterinarian’s advice and never skip or add doses to the prescribed fenbendazole dosage for your pooch. This applies regardless of what type of parasitic infection your dog is experiencing.
Potential Adverse Effects of Fenbendazole in Dogs
Regular doses of fenbendazole rarely cause side effects in dogs. Toxicity or drug overdose is also rare. However, continue to be on the lookout for a few adverse effects such as:
- Nausea
- Vomiting
- Diarrhea
- Excessive salivation
Veterinarians may prescribe combination anthelmintics that include fenbendazole and other active ingredients. Hence, you must check for more serious side effects of these medications. Praziquantel, ivermectin, and pyrantel are typical drugs used in combination with fenbendazole.
Dogs may also exhibit signs and symptoms of an allergic reaction when taking higher doses of fenbendazole. This is not directly because of the drug, but the symptoms are actually due to the substances released by the dying worms as a result of fenbendazole’s action. Hence, watch out for these cluster of symptoms suggestive of an allergic reaction:
- Itchiness
- Facial swelling
- Diarrhea
- Hives
- Cold limbs
- Seizures, shock, and comatose (severe symptoms of allergic reaction)
Take your dog to the vet immediately if you spot any of these allergic reaction symptoms.
Precautions in Giving Fenbendazole to Dogs
Fenbendazole has a high safety threshold and is safe for most dogs. But your veterinarian will likely not prescribe the medication for puppies younger than 6 weeks and dogs with underlying medical conditions.
Pregnant or lactating bitches infested with parasites may use fenbendazole carefully to prevent the worms from being passed on to the puppies. Female dogs are pregnant for around 9 weeks [2]. As such, fenbendazole use typically starts on week 6 (day 42) and continues 2 days post whelping.
Fenbendazole may be prescribed with utmost dosage caution to dogs with liver or kidney diseases. The drug is metabolized in the liver, hence, dogs will liver and kidney problems may retain fenbendazole longer inside the body.
Drug Interactions with Fenbendazole
Fenbendazole may react with certain medications such as praziquantel, pyrantel, dexamethasone, and methotrexate.
Fenbendazole exhibits synergistic effects when taken together with praziquantel and pyrantel, and the three drugs are usually combined into a single medication to kill a wider range of intestinal parasites.
Meanwhile, a study on sheep suggests that dexamethasone (a form of steroid) can decrease fenbendazole levels in the blood. This is why veterinarians typically do not give fenbendazole to dogs on steroid therapies – these are dogs who are suffering from immune-mediated illnesses, cancers, allergies, neurologic problems, and inflammatory diseases.
Now, methotrexate is a medication given to dogs and cats with lymphoma and other solid tumors. Giving fenbendazole alongside methotrexate may lead to a decreased excretion of methotrexate in the dog’s body.
Make sure your veterinarian knows about all over-the-counter drugs, prescription medications, herbal therapies, and vitamin supplements your dog is taking before starting on fenbendazole therapy.
How to Care for a Dog Taking Fenbendazole
Help your pooch heal from his intestinal worms quickly and safely! Here are some tips for dog care while he is on fenbendazole therapy:
- Give fenbendazole with food to reduce gastric upset. Most dogs can tolerate fenbendazole mixed with food.
- Measure liquid, paste, and suspension fenbendazole accurately. Use a syringe to accurately measure the medication.
- Only give fenbendazole in dosages directed by your veterinarian. Never add doses, especially when you’ve skipped a dose. Consult your veterinarian for advice when a dose is skipped. Typically, you can give the missed dose as soon as you remember, but don’t give it if the next dose is due soon. Retreatment may be required if you frequently miss doses or the medication is stopped too early.
- Continue giving the medication for the entire treatment duration prescribed by your veterinarian. Don’t stop giving fenbendazole just because you’ve seen improvements in your dog’s symptoms. It is important to finish the entire treatment duration to prevent retreatment.
The Takeaway
Fenbendazole is a safe and effective medication used to kill a wide range of worms in dogs. It can be used to eradicate most types of common parasitic worms, lungworms, giardia parasites, and Taenia pisiformis tapeworms. It kills parasites by binding to certain proteins, inhibiting cell division, and preventing the parasites from multiplying.
Dosages and treatment length are determined by your dog’s veterinarian depending on the parasitic infection your dog is experiencing. You can speed up your dog’s healing by giving fenbendazole at the proper dosage, at the right time, and for the prescribed treatment duration.
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