Giardia in dogs is treated with prescription antiparasitic medications, typically for 3 to 5 days, combined with environmental cleaning to prevent reinfection. Most dogs recover fully, but the parasite’s tough cysts make reinfection common if you don’t address the dog’s environment and hygiene at the same time as medication.
First-Line Medications
Veterinarians rely on two main drugs to clear giardia. Fenbendazole, a broad-spectrum dewormer, is considered the first-line treatment. It’s given once daily for 3 to 5 days, though some vets extend the course up to 10 days for stubborn infections. Fenbendazole is well tolerated and has a wide safety margin, which is why most vets reach for it first.
Metronidazole is the other workhorse. It’s the most commonly prescribed giardia treatment overall, and an oral suspension form is FDA-approved specifically for dogs. A typical course runs 5 to 8 days. Metronidazole can cause neurological side effects at higher doses (loss of balance, disorientation), so your vet will choose the dose carefully based on your dog’s size and health.
When one drug alone doesn’t resolve symptoms, vets often combine fenbendazole and metronidazole. A third option is a combination dewormer tablet containing febantel, pyrantel, and praziquantel, given once daily for 3 days. One drug to avoid entirely: albendazole. While it kills giardia, it can suppress bone marrow in dogs and is not considered safe for them.
What Treatment Looks Like Day to Day
Your vet will prescribe the medication and send you home with it. You’ll give the drug orally, usually mixed with food, for the prescribed number of days. Most dogs start showing improvement in diarrhea and appetite within 2 to 3 days of starting treatment, but it’s critical to finish the full course even if your dog seems better. Stopping early leaves surviving parasites in the gut, which can multiply and cause a relapse.
On the last day of treatment, give your dog a full bath. This removes fecal material and any giardia cysts clinging to the fur, especially around the hindquarters. Cysts in the coat are one of the sneakiest routes of reinfection: your dog grooms itself, swallows cysts, and the cycle starts over. A thorough bath with regular dog shampoo, focusing on the back end and legs, breaks that cycle.
Cleaning Your Home and Yard
Medication alone won’t solve a giardia problem if your dog keeps encountering cysts in its own environment. Giardia cysts are hardy. They can survive for several months in cold water and moist soil, waiting to be ingested. That means the areas where your dog sleeps, plays, and eliminates all need attention.
For hard surfaces like floors, crates, and food bowls, use a bleach solution of 3/4 cup of bleach per gallon of water. Let the solution sit on the surface for at least a few minutes before rinsing. Quaternary ammonium compounds, found in many household disinfectant sprays and wipes, also kill giardia cysts. Check the label for “alkyl dimethyl ammonium chloride” as an active ingredient.
Soft surfaces are trickier. Wash bedding, blankets, and any removable fabric covers in hot water and dry on the highest heat setting your dryer offers. Heat is effective against cysts. For yards, pick up feces immediately and daily throughout treatment. Concrete runs can be bleached; grass and dirt can’t be effectively disinfected, but removing feces promptly and keeping the area as dry as possible reduces cyst survival. Sunlight and drying conditions are your allies outdoors.
Why Reinfection Keeps Happening
Giardia is one of the most frustrating parasites to fully eliminate because the reinfection loop is so easy to trigger. Your dog sheds millions of microscopic cysts in its stool. Those cysts contaminate the fur, the yard, water bowls, and bedding. Your dog (or another dog in the household) ingests even a small number of cysts, and the infection restarts. This is why so many owners feel like treatment “didn’t work” when in reality the medication cleared the infection, but the dog picked it right back up from its own environment.
If you have multiple dogs, treat all of them simultaneously, even those without symptoms. Asymptomatic carriers shed cysts just as readily. Bathe all dogs on the last day of treatment, clean the entire living area on the same day, and pick up all yard waste. Think of it as a coordinated reset.
Supporting Your Dog’s Gut Recovery
Giardia damages the lining of the small intestine, which is why diarrhea, gas, and poor appetite are the hallmark symptoms. Even after the parasite is gone, it can take your dog’s gut a week or two to fully heal. During this time, a higher-fiber diet can help by adding bulk to stools and promoting more regular bowel movements. Your vet may recommend a temporary gastrointestinal diet or suggest adding a fiber source to your dog’s regular food.
Probiotics can also support recovery, especially if your dog was treated with metronidazole, which is an antibiotic that disrupts beneficial gut bacteria alongside the parasite. A canine-specific probiotic helps repopulate the digestive tract with healthy bacteria. Prebiotics, which are non-digestible fibers that feed those beneficial bacteria, work in tandem. Many veterinary probiotic supplements contain both. Glutamine, an amino acid that supports intestinal lining repair, is another ingredient some vets recommend during the recovery window.
Follow-Up Testing
Don’t assume the infection is gone just because symptoms improve. Giardia can linger at low levels without causing obvious diarrhea. Most vets recommend a follow-up fecal test after treatment to confirm the parasite has been eliminated. The standard test is a fecal antigen test, which detects giardia proteins in the stool and is more reliable than looking for cysts under a microscope.
Timing matters for the recheck. Testing too soon after treatment can produce a false positive because dead parasite material may still be present in the gut. Your vet will advise on the right window, which is typically a couple of weeks after the last dose. If the test comes back positive again, a second round of treatment, often using a different drug or a combination approach, is the standard next step.
Risk to Humans and Other Pets
If you’re worried about catching giardia from your dog, the risk is low. The types of giardia that infect dogs are generally not the same types that infect humans. The CDC considers dog-to-human transmission unlikely. That said, basic hygiene still applies: wash your hands after picking up stool, don’t let your dog lick your face during active infection, and keep immunocompromised family members away from cleanup duties.
Cats can carry giardia too, but cross-species transmission between dogs and cats in the same household appears uncommon. The bigger concern is dog-to-dog spread, which happens readily through shared water sources, communal play areas, and kennels. If your dog frequents a dog park or daycare, those are common pickup spots, and reinfection from outside the home is always possible even after a successful treatment course.