Ivermectin is highly effective at killing hookworms in dogs. In controlled studies, single oral doses eliminated 96% to 100% of hookworms from infected dogs, clearing both adult worms and late-stage larvae from the intestinal tract within days. It works against the major hookworm species that infect dogs and is a core ingredient in several widely used monthly heartworm prevention products that double as hookworm control.
How Ivermectin Kills Hookworms
Ivermectin paralyzes hookworms by disrupting their nervous system. The drug forces open chloride channels in the worm’s nerve and muscle cells, causing permanent paralysis. Once paralyzed, the worms detach from the intestinal wall and pass out in your dog’s stool, typically within one to three days of treatment.
Lab studies show the drug is potent across multiple life stages. It kills actively motile adult worms, damages eggs inside female worms, and destroys infective larvae at concentrations as low as 0.0025 micrograms per milliliter. In one study, dogs with heavy infections (up to 41,700 eggs per gram of feces) were given a single oral dose. By day four, no worms could be found in the intestinal tract at all. Untreated dogs, by comparison, harbored an average of 178 worms each.
Which Hookworm Species It Works Against
Dogs can be infected by several hookworm species, and ivermectin handles the most common ones. Studies confirm near-total efficacy against Ancylostoma caninum (the most widespread canine hookworm), Uncinaria stenocephala (common in cooler climates), and Ancylostoma braziliense (found in tropical and subtropical regions). A combination chewable containing ivermectin and pyrantel achieved a 99.6% reduction in worm burdens against both A. caninum and U. stenocephala in experimentally infected dogs, with no adverse effects observed.
Adults and Larvae Both Respond
One concern with any dewormer is whether it reaches worms at different developmental stages. Ivermectin handles both fourth-stage larvae (the immature worms migrating through tissue or recently arrived in the gut) and adult hookworms. In dose-titration trials, near-maximal efficacy against both stages was achieved at an oral dose of 0.024 mg/kg. Adult A. caninum required the lowest dose to clear (0.014 mg/kg), while fourth-stage larvae of U. stenocephala needed slightly more (0.044 mg/kg). Both figures fall well within the standard therapeutic range.
That said, ivermectin does not reliably kill encysted or dormant larvae that some hookworm species can “park” in a dog’s muscle tissue. These arrested larvae can reactivate weeks or months later, which is why monthly prevention matters even after a successful treatment.
Dosage: Prevention vs. Treatment
The dose of ivermectin your dog receives depends on whether the goal is prevention or active treatment. Monthly heartworm preventives that also control hookworms deliver ivermectin at about 6 micrograms per kilogram of body weight. This low dose is enough to clear hookworms picked up since the last dose and prevent new infections from establishing.
For treating an existing hookworm infection, higher doses are used. Research supports a single dose of 200 micrograms per kilogram as effective for clearing moderate to heavy infections within a week. Even doses as low as 50 or 100 micrograms per kilogram achieved complete clearance in study dogs. By comparison, another common dewormer (albendazole) eliminated only 21% to 65% of worms at standard doses in the same study, making ivermectin considerably more reliable for hookworm infections.
Breed Sensitivity and Safety
Most dogs tolerate ivermectin well at hookworm treatment doses, but certain breeds carry a genetic mutation that makes them far more sensitive to the drug. The MDR1 gene mutation, first identified in 2001, affects a protein that normally keeps ivermectin out of the brain. Dogs with this mutation can experience neurological toxicity at doses more than tenfold lower than what a normal dog tolerates safely.
The breeds most commonly affected include:
- Collies: roughly 70% carry the mutation
- Longhaired Whippets: about 65%
- Australian Shepherds and Miniature Australian Shepherds: about 50%
- McNabs and Silken Windhounds: about 30%
- Shetland Sheepdogs and English Shepherds: about 15%
- German Shepherds: about 10%
- Mixed breeds: about 5%
Signs of ivermectin toxicity include dilated pupils, drooling, tremors, difficulty walking, extreme lethargy, and in severe cases, coma. The good news is that at the low doses found in monthly heartworm preventives (6 micrograms per kilogram), even sensitive Collies showed no signs of toxicity at ten times the recommended dose. The risk increases with the higher treatment-level doses. A simple cheek swab DNA test can determine whether your dog carries the MDR1 mutation, and it’s worth doing before any higher-dose ivermectin treatment in at-risk breeds.
Emerging Hookworm Resistance
While ivermectin remains effective for the vast majority of dogs, resistant hookworm strains are starting to appear. Researchers in Florida identified an Ancylostoma caninum isolate in 2019 that was resistant to both ivermectin and other common dewormers. More recent testing in 2024, however, characterized another isolate that remained fully susceptible to ivermectin, moxidectin, and pyrantel, suggesting resistance is not yet widespread.
Resistance tends to develop in dogs that have been repeatedly treated with the same drug class, particularly in shelter and kennel environments with high infection pressure. If your dog’s fecal egg count doesn’t drop after treatment, your vet may run a fecal egg count reduction test to check whether the hookworms are responding to the medication. In confirmed resistance cases, rotating drug classes or using combination products can help.
How Ivermectin Compares to Other Dewormers
Ivermectin is not the only option for hookworms, but it consistently ranks among the most effective. In head-to-head comparisons, it outperformed albendazole significantly, clearing 100% of worms where albendazole managed only 21% to 65%. Combination products pairing ivermectin with pyrantel (another deworming compound that works through a different mechanism) achieved 100% clearance of adult A. braziliense in treated dogs.
Fenbendazole, another widely available dewormer, is also effective against hookworms and is often used for dogs that can’t receive ivermectin due to breed sensitivity. Pyrantel pamoate on its own is commonly used in puppies starting at two weeks of age. Each option has trade-offs in terms of which life stages and species they cover, but ivermectin’s broad activity against multiple hookworm species, larvae, and adults in a single dose gives it an edge for most dogs.