Plain-language dosage tables, brand comparisons, critical MDR1 breed warnings, toxicity signs, and FAQ answers — all based on FDA-approved labeling and current veterinary research from Cornell, WSU, and AAHA.
Ivermectin is a powerful antiparasitic drug with a dose range that spans more than 100-fold depending on what it is treating — and the difference between a safe dose and a toxic one can be extremely small. Never give your dog a livestock ivermectin product (cattle, horse, or sheep formulas) without veterinary supervision. These concentrated formulas — often 1% or 1.87% solutions — contain far more ivermectin per milliliter than any dog product, making accidental overdose and death a real risk. Always use FDA-approved dog-specific products at the weight range indicated on the label. If you are unsure, call your veterinarian before administering any dose. This guide is for informational purposes only and does not replace veterinary advice.
Ivermectin belongs to the macrocyclic lactone class of antiparasitic drugs, first isolated from a soil bacterium (Streptomyces avermitilis) in the 1970s — a discovery recognized with the 2015 Nobel Prize in Physiology or Medicine. It works by binding to glutamate-gated chloride channels and GABA receptors in invertebrate nerve and muscle cells, causing paralysis and death of the parasite. In healthy mammals, ivermectin cannot easily cross the blood-brain barrier at low doses — which is what makes it safe for dogs at heartworm-prevention dosing levels. In dogs with the MDR1/ABCB1 genetic mutation, however, a defective P-glycoprotein pump allows ivermectin to accumulate in the brain even at lower doses. The FDA specifically approves ivermectin for dogs at 6 mcg/kg monthly for heartworm prevention — all other uses are considered off-label and require a veterinary prescription and supervision.
Ivermectin is one of the most commonly used antiparasitic drugs in veterinary medicine — and one of the most misunderstood. The dosage range is enormous: the heartworm-prevention dose is 6 micrograms per kilogram, while mange treatment doses can reach 400 micrograms per kilogram — a difference of more than 60 times. Using the wrong dose, wrong product, or wrong species formulation can cause irreversible neurological damage or death. Here are ten facts every dog owner should understand before giving their dog any form of ivermectin.
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What is the FDA-approved ivermectin dosage for dogs? Heartworm prevention: 6 mcg/kg (2.72 mcg/lb) monthly — this is the ONLY FDA-approved oral ivermectin dose for dogsThe FDA specifically approves ivermectin for heartworm prevention in dogs at a minimum dose of 6 micrograms per kilogram of body weight, administered once monthly. This is the dose found in products like Heartgard Plus, Iverhart Plus, and generic equivalents. According to the FDA DailyMed official label for Heartgard Plus, this precise dosing is calculated per kilogram — not per pound — and the minimum effective dose must be reached to reliably eliminate heartworm larvae before they mature. All FDA-approved heartworm preventives have been tested for safety at this dose level, including in dogs with the MDR1 genetic mutation. Any other ivermectin use in dogs — for mange, ear mites, or internal parasites — is considered “extra-label” use and legally requires a veterinarian’s prescription and supervision per the Animal Medicinal Drug Use Clarification Act (AMDUCA).
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Ivermectin dosage for dogs by weight — what are the standard heartworm prevention doses? Up to 25 lbs: 68 mcg ivermectin per chewable · 26–50 lbs: 136 mcg · 51–100 lbs: 272 mcg · Over 100 lbs: appropriate tablet combination — always dose by body weight, never by breed or coat colorFDA-approved heartworm prevention chewables deliver ivermectin at weight-based doses. The three standard sizes follow the same dosing principle: small-dog tablets (for dogs up to 25 lbs) contain 68 mcg ivermectin; medium-dog tablets (26–50 lbs) contain 136 mcg; and large-dog tablets (51–100 lbs) contain 272 mcg. For dogs over 100 lbs, the appropriate combination of tablets is used. These doses all fall within the safe 6–12 mcg/kg range at their respective maximum body weights. The most important principle: always dose by your dog’s actual body weight — not by breed, size class, or visual estimate. Weigh your dog before purchasing. Giving a small-dog product to a dog who actually weighs more than 25 lbs means underdosing (reduced protection). Giving a large-dog product to a small dog means dangerous overdosing.
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Is it safe to give my dog ivermectin without a vet prescription? FDA-approved heartworm prevention chewables (Heartgard, Iverhart, Tri-Heart, generic equivalents) require a vet prescription in the U.S. · Livestock ivermectin is NOT safe to use without veterinary guidance · Never dose with horse or cattle productsIn the United States, all ivermectin-containing heartworm preventives for dogs are classified as prescription drugs — they legally require a veterinarian’s prescription. This is confirmed on every FDA DailyMed label with the statement: “Federal (U.S.A.) law restricts this drug to use by or on the order of a licensed veterinarian.” Many online pharmacies and retailers sell these products, but a valid vet prescription is required for purchase. Livestock ivermectin products — sold at Tractor Supply and farm stores without a prescription — are formulated in concentrations 10 to 100 times higher than dog products. Using them without veterinary guidance is a primary cause of ivermectin poisoning deaths in dogs. The FDA warns specifically against using large-animal ivermectin formulations in dogs. The narrow safety margin in small and herding-breed dogs makes any off-label livestock use extremely dangerous.
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What breeds are sensitive to ivermectin (MDR1/ABCB1 mutation)? Collie (~70–75% carry the mutation) · Australian Shepherd & Mini Aussie (~50%) · Shetland Sheepdog · Border Collie · Old English Sheepdog · German Shepherd · English Shepherd · McNab Shepherd · Up to 10% of mixed-breed dogs may also carry itThe MDR1 (now formally called ABCB1) gene mutation was first discovered by Dr. Katrina Mealey at Washington State University in 2001, when Collies showed toxic reactions to ivermectin at doses safe for other breeds. This 4-base-pair deletion causes a nonfunctional P-glycoprotein pump that normally prevents certain drugs from entering the brain. Up to 75% of Collies carry at least one copy of this mutation, according to peer-reviewed research published in Pharmacogenetics and confirmed by Cornell University College of Veterinary Medicine. Australian Shepherds are second, with approximately 50% affected. Critically, the AAHA (updated October 2025) confirms that FDA-approved heartworm preventive doses — the 6 mcg/kg monthly dose — have been tested and are considered safe even in MDR1-affected dogs. The risk applies to higher off-label doses used for mange treatment. Mixed-breed dogs with herding ancestry may carry the mutation even without obvious physical characteristics — genetic testing is available through WSU and UC Davis.
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What are the signs of ivermectin toxicity in dogs? Dilated pupils · Stumbling or loss of coordination (ataxia) · Tremors · Excessive drooling · Lethargy or stupor · Blindness · Seizures · Coma — call your vet or ASPCA Poison Control immediately if you see these signsIvermectin toxicity signs develop within 2–24 hours after ingestion, with most cases showing symptoms within 4–6 hours of exposure. The most frequently reported clinical signs — documented across multiple veterinary toxicology studies and by the ASPCA Animal Poison Control Center — include lethargy, ataxia (uncoordinated stumbling), excessive drooling, tremors, dilated pupils, and bradycardia (slow heart rate). Severe cases progress to blindness, seizures, respiratory failure, coma, and death. There is no specific antidote for ivermectin toxicity. Treatment is entirely supportive: induced vomiting (only by a veterinarian within 4–6 hours of ingestion), activated charcoal, IV fluids, nutritional support, and in critical cases, mechanical ventilation. Intravenous lipid emulsion (ILE) has emerged as a promising supportive treatment in severe cases, described in a 2025 peer-reviewed case report in Veterinary Medicine and Science. Recovery can take days to several weeks and may require extended hospital stays. The earlier treatment begins, the better the prognosis.
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What is the ivermectin dosage for dogs in ml (for oral liquid)? This question reflects interest in off-label livestock products — this is dangerous without veterinary supervision · FDA-approved dog chewables are the only safe self-administered format · If your vet has prescribed oral liquid ivermectin, follow their specific ml calculation exactlyThe interest in “ivermectin dosage in ml” typically reflects owners considering livestock solutions (0.08% sheep drench, 1% cattle/swine formula, or 1.87% horse paste). These formulations contain radically different concentrations: 1% ivermectin solution contains 10,000 mcg per ml, while the heartworm-prevention dose for a 30-lb dog is only about 82 mcg. Even a single extra drop of 1% solution can represent a massive overdose. If a veterinarian has specifically prescribed an oral ivermectin liquid for your dog’s mange or other off-label condition, your vet will provide the exact ml dose for your dog’s weight and the specific product concentration. No general ml dose chart is published here because the appropriate ml volume depends entirely on the concentration of the specific product — and that variable makes a general chart dangerous. Request the exact ml figure from your vet in writing along with the product concentration, and verify the math before administering.
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What FDA-approved brands of ivermectin heartworm prevention are available for dogs? Heartgard Plus (ivermectin + pyrantel, Boehringer Ingelheim) · Iverhart Plus (ivermectin + pyrantel, Virbac) · Iverhart Max (adds praziquantel) · Tri-Heart Plus (generic ivermectin + pyrantel) · Heart Defense (generic equivalent) · All require a vet prescription in the U.S.Several FDA-approved heartworm prevention products for dogs contain ivermectin as the active heartworm preventive ingredient. Heartgard Plus by Boehringer Ingelheim is the most recognized brand, containing ivermectin and pyrantel pamoate. Iverhart Plus and Iverhart Max by Virbac contain the same combination, with the Max version adding praziquantel for tapeworm coverage (ANADA 200-302). Tri-Heart Plus is a generic bioequivalent approved by the FDA. Heart Defense (ANADA 200-338) is another generic alternative. All have been tested for safety at FDA-approved doses including in MDR1-affected breeds per their official labels. Generic ivermectin-based chewables are clinically equivalent to Heartgard at lower cost — the Bestiepaws veterinary guide updated December 2025 cites Vetster data showing annual heartworm preventive costs for a 40-lb dog range from $70–$200 depending on brand. Ask your vet whether a generic equivalent is appropriate for your dog.
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How does ivermectin dosage for mange differ from heartworm prevention? Mange doses are 50–100x higher than heartworm prevention · Sarcoptic mange: 300–600 mcg/kg · Demodectic mange: 300–600 mcg/kg, escalated gradually · These off-label doses require a vet prescription and careful monitoring — never use without professional guidanceThe dosing difference between heartworm prevention and mange treatment is enormous — and this gap is where most serious ivermectin accidents occur. Heartworm prevention uses 6 mcg/kg monthly. Sarcoptic mange treatment typically requires 300–600 mcg/kg, and demodectic mange protocols may start lower (around 100 mcg/kg) and escalate gradually over several weeks, reaching 600 mcg/kg in some protocols — doses more than 100 times higher than heartworm prevention. At these high off-label doses, even dogs without the MDR1 mutation can develop toxicity. Dogs with the MDR1 mutation can develop severe neurological toxicity at doses as low as 100 mcg/kg per PMC toxicology review data. Off-label ivermectin for mange is prescription-only and requires direct veterinary supervision, baseline MDR1 testing for at-risk breeds, gradual dose escalation, and monitoring for early toxicity signs. Modern prescription alternatives such as Bravecto (fluralaner), NexGard (afoxolaner), and Credelio are FDA-approved for mite treatment and are safer options for MDR1-affected breeds per AAHA October 2025 guidance.
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Can puppies receive ivermectin heartworm prevention? Yes — but not before 6 weeks of age · FDA-approved heartworm preventives are labeled safe for puppies 6 weeks and older · Heartworm prevention should start at 8 weeks of age and continue year-round for lifeAll major FDA-approved ivermectin-based heartworm preventives are labeled safe for puppies 6 weeks of age and older, per the official DailyMed label for Heartgard Plus and confirmed by PetMD’s veterinary review. They are also considered safe for pregnant and breeding females at the heartworm-prevention dose. The American Heartworm Society and CAPC recommend starting puppies on heartworm prevention at 8 weeks of age — and continuing monthly for life. Since heartworm disease has been diagnosed in all 50 U.S. states per CAPC’s 2025 annual forecasts, no geographic location makes year-round prevention unnecessary. A heartworm test before starting prevention in dogs over 6 months of age is recommended — starting a heartworm preventive in a dog already carrying adult heartworms can cause a severe reaction as microfilariae in the bloodstream are rapidly killed. Always confirm heartworm-negative status before beginning any prevention product in an adult dog with unknown medical history.
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What should I do if my dog ingests too much ivermectin? Call your vet immediately OR ASPCA Animal Poison Control: 888-426-4435 · Pet Poison Helpline: 844-520-4632 · Do NOT induce vomiting at home — this must be done by a vet only · Bring the product packaging · Time is critical — early treatment improves outcomeIvermectin toxicity is a veterinary emergency. If your dog received the wrong product, wrong dose, or ingested livestock ivermectin, contact a veterinarian or poison control center immediately — do not wait for symptoms to appear. The ASPCA Animal Poison Control Center (888-426-4435) and Pet Poison Helpline (844-520-4632) are available 24 hours a day, 7 days a week, including weekends and holidays. When you call, have ready: the exact product name and concentration (e.g., “ivermectin 1% injection”), the amount your dog may have received, your dog’s current weight, and any symptoms you are observing. Vomiting induction, if appropriate, can only be safely performed within 4–6 hours of ingestion and must be done under veterinary supervision — attempting it at home in a dog already showing neurological signs can worsen the outcome. Prognosis is generally fair to good with early, aggressive supportive care, though severe cases may require weeks of hospitalization including mechanical ventilation.
Sources: FDA DailyMed Heartgard Plus label (6 mcg/kg minimum; 2.72 mcg/lb; ivermectin + pyrantel; puppies 6 wks+; pregnant safe; Boehringer Ingelheim Vetmedica); FDA DailyMed Heart Defense ANADA 200-338 (68 mcg/136 mcg/272 mcg tablet sizes; weight ranges; Rx required); Cornell University College of Veterinary Medicine MDR1 guide (ABCB1 gene; P-gp function; herding breeds; 4-bp deletion; neurotoxicity); Washington State University PrIMe MDR1 program (75% of Collies affected; breed list; genetic testing); AAHA “White feet don’t treat” Oct 2025 (FDA-approved doses safe MDR1 dogs; isoxazolines tested safe; 10% mixed breeds affected); PetMD ivermectin toxicity (MDR1 0.1 mg/kg toxic vs 2.5 mg/kg normal dogs; 6-wk minimum; pregnant safe; neurologic signs 2–24 hr); ASPCA APCC (ivermectin Rx only; poison control 888-426-4435); PMC macrocyclic lactone toxicology (ataxia, drooling, tremors, mydriasis, bradycardia, coma, death; ILE emerging treatment); Bestiepaws ivermectin guide Dec 2025 (dose ranges by use; 6 mcg/kg heartworm; 300-600 mcg/kg mange; off-label vet only; annual cost $70–200); SpectrumCare ivermectin toxicity Apr 2026 (call vet/ASPCA/PPH immediately; no home vomiting induction; MDR1 at-risk breeds); PMC ILE case report Vet Med Sci 2025 (intralipid emulsion therapy; Shih Tzu case; lipid sink mechanism)
The dosage table below reflects FDA-approved heartworm prevention products only. Ivermectin doses for mange, mites, or other off-label conditions are prescribed individually by a veterinarian and are NOT included here because they require direct veterinary supervision and MDR1 testing for at-risk breeds. Never attempt to calculate or administer a mange dose from this table.
Table 1 — Standard FDA-Approved Heartworm Prevention Tablet Sizes by Dog Weight
| Dog Weight | Tablet Size | Ivermectin (mcg) | Pyrantel (mg)* | Dose Frequency |
|---|---|---|---|---|
| Up to 25 lbs | Small (Blue/Magenta) | 68 mcg | 57 mg | Once monthly |
| 26 – 50 lbs | Medium (Blue) | 136 mcg | 114 mg | Once monthly |
| 51 – 100 lbs | Large (Green) | 272 mcg | 228 mg | Once monthly |
| Over 100 lbs | Appropriate combo | As directed | As directed | Once monthly |
*Pyrantel pamoate is included in combination products (Heartgard Plus, Iverhart Plus, Tri-Heart Plus) for roundworm and hookworm control. Ivermectin-only products exist but are less common. Source: FDA DailyMed Heartgard Plus label; FDA ANADA 200-338 Heart Defense label.
Table 2 — Ivermectin Dose Per Kilogram (mcg/kg) at Each Weight Bracket
| Dog Weight Range | Min. Ivermectin Dose | Max. Ivermectin Dose | FDA Target (mcg/kg) |
|---|---|---|---|
| 6 – 25 lbs (2.7–11.4 kg) | 6.0 mcg/kg (at 25 lbs) | 25 mcg/kg (at 6 lbs) | ≥ 6 mcg/kg |
| 26 – 50 lbs (11.8–22.7 kg) | 6.0 mcg/kg (at 50 lbs) | 11.5 mcg/kg (at 26 lbs) | ≥ 6 mcg/kg |
| 51 – 100 lbs (23.2–45.5 kg) | 6.0 mcg/kg (at 100 lbs) | 11.7 mcg/kg (at 51 lbs) | ≥ 6 mcg/kg |
The FDA requires a minimum of 6 mcg/kg to reliably eliminate heartworm larvae. All three weight brackets are designed so the minimum-weight dog in each range receives close to the target dose, and the maximum-weight dog receives exactly or slightly above the minimum. Source: FDA DailyMed Heartgard Plus; FDA ANADA 200-338.
Table 3 — Ivermectin Use Summary by Indication (Vet Guidance Required for Off-Label)
| Use / Indication | Dose Range | Frequency | Prescription? | MDR1 Risk? |
|---|---|---|---|---|
| Heartworm Prevention | 6 mcg/kg | Monthly | Yes (Rx) | Low — safe at Rx dose even in MDR1 dogs |
| Roundworms / Hookworms (off-label) | ~100 mcg/kg | Once | Yes (Vet only) | Moderate |
| Sarcoptic Mange (off-label) | 300–600 mcg/kg | Weekly × 2–4 wks | Yes (Vet only) | HIGH — test MDR1 first |
| Demodectic Mange (off-label) | 100–600 mcg/kg escalated | Daily, escalated | Yes (Vet only) | HIGH — test MDR1 first |
| Ear Mites (off-label) | 200–400 mcg/kg | Once or twice | Yes (Vet only) | HIGH — test MDR1 first |
Off-label doses are provided for informational context only. All off-label ivermectin use in dogs requires a vet prescription and active supervision. Source: Bestiepaws ivermectin dosage guide Dec 2025; PetMD ivermectin; PMC macrocyclic lactone toxicology; AAHA Oct 2025.
Sources: FDA DailyMed Heartgard Plus official label (Boehringer Ingelheim; ivermectin + pyrantel; 6 mcg/kg; 2.72 mcg/lb; puppies 6 wks; pregnant safe; 10× dose = 60 mcg/kg no toxicity Collies); FDA ANADA 200-338 Heart Defense label (68/136/272 mcg tablet sizes; weight brackets; federal Rx required; generic bioequivalent); Bestiepaws ivermectin for dogs guide Dec 2025 (dose ranges by use; heartworm 6 mcg/kg; sarcoptic 300–600 mcg/kg; ear mites 200–400 mcg/kg; off-label vet only); PetMD ivermectin toxicity (approved 0.024 mg/kg oral; tolerates to 2.5 mg/kg normal; MDR1 toxic at 0.1 mg/kg; neurologic signs 2–24 hr); AAHA Oct 2025 MDR1 article (FDA-approved doses tested safe MDR1; isoxazolines safe MDR1); PMC macrocyclic lactone toxicology article (dose ranges; ASPCA APCC data; 10× HWP dose no toxicity MDR1 Collies)
Sources: FDA DailyMed Heartgard Plus (6 mcg/kg approved dose); PetMD ivermectin toxicity (MDR1 toxic at 100 mcg/kg; normal dogs 2,500 mcg/kg); Cornell University College of Veterinary Medicine MDR1 guide; WSU PrIMe MDR1 program (70–75% Collies; 50% Aussies; 10% mixed breeds); AAHA Oct 2025 (FDA doses safe MDR1); Vetlexicon ivermectin toxicity (half-life 76–80 hr; peak plasma 3–5 hr)
The MDR1 (or ABCB1) gene produces a protein called P-glycoprotein, which acts as a biological pump at the blood-brain barrier, actively preventing certain drugs from accumulating in the brain. When both copies of this gene are mutated (homozygous), a dog has essentially no functional P-glycoprotein — meaning drugs like ivermectin can freely enter brain tissue and cause neurological damage even at relatively low doses. Dogs with one mutated copy (heterozygous) have reduced but some P-glycoprotein function and are at intermediate risk. Crucially, every FDA-approved heartworm preventive has been specifically tested in MDR1-affected dogs at the standard 6 mcg/kg dose and has been confirmed safe by the AAHA (October 2025 review). The danger only appears at the much higher off-label doses used for mange and mite treatment. Washington State University and UC Davis Veterinary Genetics Laboratory offer commercial MDR1/ABCB1 genetic tests for approximately $60–$80 via cheek swab — highly recommended before any high-dose antiparasitic treatment in herding breeds or unknown-mix dogs.
A cheek swab DNA test — simple enough to do at home — can confirm whether your dog carries 0, 1, or 2 copies of the ABCB1 mutation. Three accredited testing options: Washington State University PrIMe Program (prime.vetmed.wsu.edu) — the lab that discovered the mutation; UC Davis Veterinary Genetics Laboratory (vgl.ucdavis.edu) — peer-reviewed testing service; and Embark Dog DNA Test and similar commercial tests that include MDR1 screening in their broader health panel. Results take 1–3 weeks. Testing is especially important before your vet considers any higher-dose antiparasitic treatment for mange or mites, or before using any medication on WSU’s MDR1 problem-drug list (which includes certain sedatives, antidiarrheals like Imodium/loperamide, and chemotherapy drugs in addition to ivermectin).
Sources: Cornell University College of Veterinary Medicine MDR1/ABCB1 guide (P-gp function; herding breeds; 4-bp deletion; heterozygous vs homozygous risk); WSU PrIMe MDR1 program (75% Collies; breed list updated 2021; MDR1Caddie consulting service); UC Davis VGL multidrug sensitivity breed list (Australian Shepherd; Border Collie; Black Mouth Cur; Carolina Dog; Chinook; Collie; English Shepherd; German Shepherd; McNab; Old English Sheepdog; Shetland Sheepdog; Silken Windhound; White Shepherd; Longhaired Whippet); AAHA “White feet don’t treat” Oct 2025 (homozygous N/M unpredictable; 10% mixed breeds; mixed breeds can be homozygous without obvious herding appearance; cats also affected 4% feline population); PetMD MDR1 gene (70% Collies; 50% Aussies; hereditary; cheek swab test commercially available; not just vet-administered)
This is the question that causes the most serious ivermectin emergencies in dogs — and the answer is a clear no without direct veterinary guidance. Here is the exact problem: horse ivermectin paste is typically 1.87% concentration, meaning each gram contains 18,700 mcg of ivermectin. A single gram of that paste contains enough ivermectin to treat approximately 70 dogs at the heartworm-prevention dose. Even a tiny amount — a smear too large, a miscalculation of a decimal point — results in a massive overdose. Cattle pour-on formulas (typically 0.5%) are also highly concentrated and are not designed for oral use in dogs. The FDA specifically warns against using livestock ivermectin products in dogs. The ASPCA Animal Poison Control Center reports that accidental ingestion of horse dewormer paste is one of the most common causes of ivermectin poisoning calls. If your vet has specifically prescribed an off-label liquid ivermectin protocol using a diluted livestock product, they will provide the exact ml dose, the specific concentration, and how to prepare the dilution — never attempt this without those explicit written instructions.
Ivermectin-based heartworm preventives are given once every 30 days — not once a month by calendar date, but every 30 days. This interval is critical because ivermectin works by eliminating heartworm larvae (Dirofilaria immitis) that entered the body during the preceding 30 days before they can mature into adult worms. If more than 45 days pass between doses, some larvae may escape elimination and continue developing. Missing two consecutive doses during mosquito season significantly increases heartworm risk. The American Heartworm Society and CAPC recommend year-round prevention in all 50 U.S. states — because heartworm has been diagnosed in every state, and because stopping prevention during winter months and restarting in spring creates dangerous gaps. If your dog has missed a dose, give it as soon as you remember and restart the 30-day schedule from that date — do not double-dose. After missing more than 45 days, consult your vet about retesting before continuing.
Ivermectin-based products (Heartgard Plus, Iverhart Plus, Tri-Heart Plus) are proven, cost-effective, and have a decades-long safety record for heartworm prevention. They are the most affordable option — generic versions cost significantly less than newer combination products. However, newer products like Simparica Trio (sarolaner + moxidectin + pyrantel) and Credelio Quattro (lotilaner + moxidectin + praziquantel + pyrantel) offer broader parasite coverage in a single monthly dose, adding protection against fleas, ticks, and tapeworms that ivermectin alone does not provide. For MDR1-affected breeds specifically, the AAHA October 2025 review confirms that manufacturers of all current FDA-approved combination products — including those with isoxazolines (sarolaner, lotilaner, afoxolaner) — have tested their products for safety in MDR1-affected dogs. The best choice for your dog depends on your geographic parasite risk, your dog’s breed and MDR1 status, and cost — a conversation well suited for your annual vet visit.
If your dog is showing any of the following signs after receiving ivermectin — stumbling, wobbling, dilated pupils, trembling, excessive drooling, sudden extreme sleepiness, or seizures — this is a veterinary emergency. Do not wait to see if they improve. Do not try to induce vomiting at home. Call immediately: your nearest veterinary emergency clinic, ASPCA Animal Poison Control (888-426-4435), or Pet Poison Helpline (844-520-4632). Bring the product packaging with you to the emergency clinic. The earlier supportive care begins, the better the outcome. Dogs in severe cases may need IV fluids, sedation, anti-seizure medication, nutritional support via feeding tube, and mechanical ventilation — treatment that can only be provided in a veterinary facility. In mild cases caught within 4–6 hours of ingestion, a vet may be able to perform decontamination that limits how much of the drug is absorbed.
Sources: ASPCA APCC “What is Ivermectin” (horse dewormer ingestion common cause; Rx only; poison control 888-426-4435; do not use large-animal products); Pet Poison Helpline (dilated pupils, tremors, drooling, seizures, coma, death signs; aggressive treatment needed; 844-520-4632); SpectrumCare ivermectin toxicity Apr 2026 (no home vomiting; call vet/ASPCA/PPH; product packaging; early treatment prognosis); American Heartworm Society guidelines 2023 (30-day interval; year-round all 50 states; retest after gap); AAHA Oct 2025 (isoxazolines tested safe MDR1; manufacturer safety data); Bestiepaws ivermectin Dec 2025 (Heartgard Plus vs combination products; generic equivalents; cost $70–200/yr); FDA ANADA 200-338 (Rx required federal law; licensed vet required); PMC ILE 2025 (ILE emerging supportive treatment; lipid sink mechanism)
Use the buttons below to locate the right resource near you — whether you need a heartworm prescription, MDR1 testing, or emergency help after a suspected ivermectin overdose.
- Step 1 — Get a heartworm test first. Before starting any heartworm preventive for the first time, or after a gap of more than 45 days, your dog needs a heartworm blood test. Starting ivermectin in a dog with existing adult heartworms can cause a severe microfilaricidal reaction. A simple in-clinic blood test takes minutes and protects your dog from this dangerous scenario.
- Step 2 — Know your dog’s weight — exactly. Weigh your dog at home (bathroom scale: weigh yourself, then yourself holding the dog) or at your vet clinic. Every ivermectin dose is calculated per kilogram or pound of body weight — estimating by visual appearance leads to under- or overdosing. This step is non-negotiable.
- Step 3 — For herding breeds or unknown mixes, ask about MDR1 testing. If your dog is a Collie, Australian Shepherd, Sheltie, Border Collie, Old English Sheepdog, or a mix of unknown heritage, ask your vet about an ABCB1/MDR1 DNA test before beginning any high-dose antiparasitic treatment. A cheek swab test from WSU or UC Davis costs approximately $60–$80 and provides lifelong guidance for medication decisions.
- Step 4 — Only use FDA-approved dog-specific products. Purchase Heartgard Plus, Iverhart Plus, Tri-Heart Plus, Heart Defense, or their pharmacy-dispensed equivalents. Never use livestock ivermectin (horse paste, cattle pour-on, or sheep drench) on your dog without specific written veterinary instructions including exact ml dose and product concentration. The concentration difference is so large that a tiny measurement error can be lethal.
- Step 5 — Give monthly without gaps and store correctly. Set a phone calendar reminder for the same day each month. Store your dog’s heartworm preventive away from direct light per package instructions. If a dose is missed, administer it as soon as remembered and resume the monthly schedule. If more than 45 days are missed, contact your vet before giving the next dose. Keep the ASPCA Poison Control number (888-426-4435) saved in your phone for emergencies.
This guide is independently researched for informational purposes only. It does not constitute veterinary medical advice and does not replace a consultation with a licensed veterinarian. Ivermectin is a prescription drug in the United States — a valid prescription from a licensed veterinarian is legally required to purchase heartworm preventives. Off-label ivermectin use for mange, mites, or other conditions requires direct veterinary supervision. All ivermectin overdoses are medical emergencies — contact the ASPCA Animal Poison Control Center (888-426-4435) or an emergency animal hospital immediately if overdose is suspected. Drug dosages and safety data were current as of April 2026; always verify with your veterinarian before administering any medication.
Primary sources: FDA DailyMed Heartgard Plus official label (ivermectin + pyrantel pamoate; 6 mcg/kg minimum; 2.72 mcg/lb; puppies 6 wks+; pregnant/breeding safe; 10× dose 60 mcg/kg no toxicity MDR1 Collies; Boehringer Ingelheim Vetmedica; federal Rx required); FDA DailyMed Heart Defense ANADA #200-338 (68/136/272 mcg tablet sizes; up to 25/26–50/51–100 lb weight brackets; ivermectin + pyrantel; Rx required federal law; generic bioequivalent); FDA Animal Drugs at FDA ANADA 200-302 Iverhart Plus (ivermectin + pyrantel; praziquantel in Max; 6 mcg/kg; Virbac); Cornell University College of Veterinary Medicine MDR1/ABCB1 guide (P-gp function; blood-brain barrier; herding breeds; 4-bp deletion; heterozygous vs homozygous; fatal reactions; cheek swab test; Nov 2023 updated); Washington State University PrIMe MDR1 program (75% Collies; ~50% Aussies; breed list 2021; MDR1Caddie consulting; WSU WADDL testing lab); UC Davis Veterinary Genetics Laboratory multidrug sensitivity MDR1 breed list (Australian Shepherd; Border Collie; Black Mouth Cur; Carolina Dog; Chinook; Collie; English Shepherd; German Shepherd; McNab; Old English Sheepdog; Shetland Sheepdog; Silken Windhound; White Shepherd; Longhaired Whippet cross; test $60–80 cheek swab); AAHA “White feet don’t treat: Considerations for dogs with MDR1 mutations” published October 2025 (FDA-approved heartworm preventive doses safe MDR1; all major antiparasitic manufacturers tested MDR1 dogs at FDA doses; isoxazolines safe; 10% mixed breeds homozygous possible without herding appearance; cats 4% affected); PetMD ivermectin toxicity updated Nov 2022 (MDR1 toxic 0.1 mg/kg vs normal 2.5 mg/kg; FDA-approved HWP doses safe MDR1; puppies 6+ wks; pregnant safe; neurologic signs 2–24 hr; no approved OTC in U.S.); PMC macrocyclic lactone toxicology (ASPCA APCC data; ataxia, drooling, tremors, mydriasis, bradycardia dominant signs; ILE emerging; horse paste/livestock feces common exposure; 0.06 mg/kg 10× HWP safe MDR1 Collies; coma/death severe cases); PMC intralipid emulsion case report Vet Med Sci 2025 (ILE treatment Shih Tzu ivermectin toxicosis; lipid sink mechanism; 0.1–0.6 mg/kg demodex dose range); ASPCA “What is Ivermectin” Sep 2021 updated (poison control 888-426-4435; Rx required; do not use large-animal products dogs; multiple formulations); Pet Poison Helpline ivermectin page (dilated pupils, tremors, drooling, seizures, coma, death; aggressive treatment required; 844-520-4632); SpectrumCare ivermectin toxicity Apr 2026 (call vet/ASPCA/PPH immediately; no home vomiting; bring packaging; MDR1 risk factor; early treatment prognosis fair-good; possible weeks hospitalization; mechanical ventilation severe); Vetlexicon ivermectin toxicity (signs 2–24 hr; persist 3 days to 1 wk; peak plasma 3–5 hr post-oral; half-life 76–80 hr; GABA mechanism overdose); Bestiepaws ivermectin for dogs complete guide Dec 2025 (dose ranges heartworm 6 mcg/kg; sarcoptic 300–600 mcg/kg; ear mites 200–400 mcg/kg; internal parasites 100 mcg/kg off-label; Nobel Prize 2015; glutamate-gated Cl channels GABA; Vetster cost data $70–200/yr 40-lb dog; generic bioequivalent; FDA warns counterfeit online; Rx required U.S.)