Introduction
Giardia is a very common intestinal parasite that infects dogs. It is estimated that over 1-10% of dogs in the United States have giardia at any given time1. Giardia attaches to the intestinal wall and causes an infection known as giardiasis. This infection can lead to severe gastrointestinal symptoms in dogs.
The most common symptoms of giardiasis in dogs include: diarrhea (often yellow and foul-smelling), vomiting, gas, abdominal discomfort, and weight loss2. Giardia prevents proper absorption of nutrients, damages the intestinal lining, and causes inflammation in the intestines. While some dogs show no symptoms, giardia can cause severe illness in others. Puppies are especially susceptible.
What is Fenbendazole?
Fenbendazole is an anthelmintic drug, which means it kills parasites. It belongs to the benzimidazole class of drugs and works by interfering with a parasite’s energy metabolism and ability to absorb nutrients (1).
Specifically, fenbendazole inhibits polymerization of microtubules, disrupting structural integrity and functions vital to parasites. It is effective against roundworms, hookworms, whipworms, tapeworms, pinworms, as well as Giardia (2).
In veterinary medicine, fenbendazole is often used to treat and control roundworms, hookworms, whipworms, and tapeworms in dogs, cats, cattle, sheep, horses, fish, and birds. It is considered a broad-spectrum dewormer. The drug is available in oral tablet, granule, paste, and suspension formulations (3).
While not approved for human use, fenbendazole has also shown potential anti-cancer effects in some preliminary studies (1, 2). However, more research is needed to evaluate its efficacy and safety as a cancer treatment.
Effectiveness Against Giardia
Fenbendazole has been shown to be highly effective at killing Giardia in dogs. One study found that a 5-day course of fenbendazole eliminated Giardia cysts in 100% of infected dogs (https://www.frontiersin.org/articles/10.3389/fvets.2021.626424). The anti-parasitic effect of fenbendazole works by disrupting the microtubules that help Giardia parasites absorb nutrients, leading to their death.
However, some studies have found lower efficacy rates. One study found fenbendazole only eliminated Giardia in 17% of dogs after 3 days of treatment (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9621113/). This is likely because Giardia cysts are resistant to many medications. Overall though, fenbendazole remains one of the most effective treatments for clearing Giardia infections when given at appropriate dosages over 5-7 days.
Dosage Guidelines
The typical dosage of fenbendazole for treating giardia in dogs is 50mg/kg once a day for 3-5 days. The exact dosage and duration is based on the dog’s weight:
- Small dogs (under 10 lbs): 50 mg/kg once daily for 5 days
- Medium dogs (11-25 lbs): 50 mg/kg once daily for 5 days
- Large dogs (26-50 lbs): 50 mg/kg once daily for 5 days
- Giant dogs (over 50 lbs): 50 mg/kg once daily for 3-5 days
For example, a dog weighing 30 lbs would get a dosage of around 681 mg per day. Always follow your veterinarian’s dosage recommendations.
According to one study, fenbendazole administered at 50 mg/kg once daily for 5 days was highly effective at eliminating giardia cysts in dogs (Barr, 1994). Other research also supports the efficacy and safety of this fenbendazole dosage for treating giardiasis (Ciuca et al., 2021).
Administering the Medication
The easiest way to administer fenbendazole to dogs is to give it with food. Try mixing the medication into a small amount of canned dog food, peanut butter, cheese spreads, or pill pockets. Make sure your dog eats all of the food so that they get the full dosage.
Here are some tips for successfully giving a dog pills:
- Place the pill in a small amount of creamy peanut butter, meat baby food, or cream cheese. Let your dog lick it directly off a spoon or your finger.
- Hide the medication in a “pill pocket” treat specifically designed for hiding pills. Just place the pill inside and pinch the treat closed.
- Crush the pills and mix the powder thoroughly into your dog’s wet food. Make sure they eat all of their food.
- Use a pill gun or piller to place the pill far back on your dog’s tongue so they swallow it. But take caution not to harm their throat.
- If your dog is stubborn, gently hold their snout closed once the pill is in their mouth. Stroke their throat until they swallow.
Be patient and stay calm when giving your dog medication. Don’t force them as that can create a negative association.
Safety and Side Effects
Fenbendazole is generally safe for dogs when administered at the proper dosage. According to Triangle Animal Clinic, side effects are rare when given as directed. However, some potential side effects can occur.
The most common side effects are gastrointestinal effects like vomiting, excessive drooling, and diarrhea (https://triangleanimalclinic.com/wp-content/uploads/2021/09/panacur-fenbendazole.pdf). VCA Animal Hospitals also lists increased drinking, increased urination, and increased appetite as potential side effects (https://vcahospitals.com/know-your-pet/fenbendazole). These side effects are usually mild and resolve on their own once the medication is finished.
In very rare cases, dogs may experience an allergic reaction to fenbendazole. Signs of an allergic reaction include hives, swelling, and trouble breathing. If these occur, stop giving the medication and contact your veterinarian immediately.
To help prevent side effects, it’s important to give fenbendazole exactly as prescribed by your vet. Never give more than the recommended dosage. Contact your vet if side effects are severe or do not go away after treatment is completed.
Other Treatment Options
In addition to fenbendazole, there are some other treatment options for giardia in dogs that veterinarians may recommend:
Metronidazole – This is an antibiotic that is commonly prescribed to treat giardia. According to one study, metronidazole is effective at eliminating giardia parasites with a success rate of 85-100% (https://www.ncbi.nlm.nih.gov/books/NBK554776/). The typical dosage is 25 mg/kg given twice daily for 5-7 days. Metronidazole can cause side effects like vomiting and loss of appetite in some dogs.
Quinacrine – This drug was previously used to treat malaria in humans. Veterinarians may prescribe quinacrine to treat giardia in dogs, often in combination with metronidazole. According to the Merck Veterinary Manual, quinacrine is approximately 70% effective at clearing giardia infection (https://www.merckvetmanual.com/digestive-system/diseases-of-the-stomach-and-intestines-in-small-animals/giardiasis-in-small-animals). The typical dosage for dogs is 6.6 mg/kg once daily for 5 days.
Dietary Changes – Making some dietary changes may help shorten the duration of giardia symptoms. The Merck Veterinary Manual recommends feeding small, bland, low-fat meals during treatment (https://www.merckvetmanual.com/digestive-system/diseases-of-the-stomach-and-intestines-in-small-animals/giardiasis-in-small-animals). Probiotics and digestive enzymes may also help support the gastrointestinal system.
Prevention
Preventing giardia infections in dogs requires proper hygiene and avoiding contaminated sources of water. Here are some tips for prevention:
- Pick up and dispose of dog feces promptly to prevent contamination of soil and water sources. Feces should be bagged and placed in the trash, not composted.
- Clean food and water bowls daily with soap and hot water to remove any cysts.
- Bathe dogs regularly with a gentle shampoo to help remove cysts from their coat.
- Avoid letting dogs drink from puddles, ponds, lakes or streams where Giardia may be present. Provide fresh, clean drinking water instead.
- Disinfect surfaces like kennels, crates, floors using bleach or other disinfectants. Steam cleaning carpets can also help.
- Practice good hand hygiene after handling pets or picking up feces and before preparing food.
While challenging, consistently following hygiene and contamination prevention steps can greatly reduce the risk of Giardia transmission between infected dogs, humans, and the environment.
When to See a Vet
In most cases, giardia infections in dogs can be successfully treated at home with fenbendazole. However, veterinary attention is recommended if symptoms persist after treatment or if your dog experiences severe diarrhea or dehydration.
Some signs that indicate you should take your dog to the vet include:
- Diarrhea continues more than 2-3 days after completing fenbendazole treatment
- Bloody diarrhea or black, tarry stools
- Lethargy, weakness, or lack of appetite
- Signs of dehydration such as dry gums, sunken eyes, or skin that lacks elasticity
- Frequent vomiting or inability to keep medications down
- Weight loss of more than a few pounds
Severe dehydration can cause electrolyte imbalances and even renal failure. It’s important to seek prompt veterinary treatment if your dog shows any signs of moderate to severe dehydration. Your vet can provide IV fluids, anti-nausea medications, and electrolyte supplementation to restore fluid balance and help resolve giardia faster.
In some cases, different medications may be needed if fenbendazole does not eliminate the infection. Your vet can run additional tests and prescribe alternative treatments as needed to help your dog fully recover.
Conclusion
In conclusion, fenbendazole is an effective treatment for dogs with giardia at a typical dosage of 50 mg/kg once daily for 5-7 days. It’s important to accurately weigh your dog and administer the medication as prescribed to properly clear the infection. Giardia can cause significant gastrointestinal illness in dogs if left untreated, so following veterinary recommendations for medication dosage and additional testing is crucial.
While fenbendazole is safe for most dogs, potential side effects like vomiting and diarrhea should be monitored. Some dogs may require multiple treatment courses or alternative medications like metronidazole if the giardiasis persists. Preventing re-infection through proper hygiene and limiting access to contaminated water or soil is also key.
With the right treatment plan, dogs with giardia can make a full recovery. Stay in close contact with your veterinarian throughout the treatment process to ensure the infection is fully eliminated.