MDR1 drug sensitivity in dogs: the ABCB1 gene, the test, and the drugs to flag in India

Signs of MDR1 drug sensitivity

The 10 signs to watch for are listed below. Any one of them is a reason to consult your nearby vet; none of them is a diagnosis.

• Stumbling, wobbling or a drunken walk hours after a dose
• Tremors or twitching in the face and limbs
• Drooling far more than the dog normally does
• Pupils wide open and not shrinking in bright light
• Apparent blindness, walking into furniture and doorways
• Vomiting with sudden weakness
• Deep drowsiness that slides into stupor
• Seizures
• A slow heartbeat with laboured breathing
• Collapse and coma

Breeds on this site that document this condition

Each breed page below carries the figure for this condition with its denominator and its source. The 10 breeds listed are the ones on this site that document it, not a ranking of risk.

What MDR1 drug sensitivity is, and which dogs carry it

MDR1 drug sensitivity is a broken drug pump rather than an illness a dog feels. The gene, now correctly called ABCB1 and formerly called MDR1, encodes P-glycoprotein, which limits drug distribution to the brain and enhances the excretion of many drugs. A four base pair deletion shifts the reading frame and generates stop codons that terminate P-glycoprotein synthesis early, so a dog with two copies never builds a working pump.

Every dog on earth has the MDR1 gene, which is why Washington State University asks people to stop saying MDR1 positive. All animals carry ABCB1 and are therefore positive by that phrasing, and the university's own page says terms reflecting the animal's actual genotype, mutant or normal, should be used instead. The distinction is not pedantry at an Indian counter. An owner told the dog is MDR1 positive has been told nothing about whether the dog can be given a drug.

What the pump does, and where it sits

P-glycoprotein is an integral part of the blood-brain barrier and works as a drug-transport pump there, moving a variety of drugs from the brain back into the blood. Cornell's Riney Canine Health Center puts the same mechanism in owner terms, that the protein helps eliminate drugs after administration and keeps certain drugs and toxins out of the brain and other organs, and that when it is not functioning correctly those substances can build up or cross into the brain. The pump is not only in the brain, and that has a second consequence. Substrate drugs also show less biliary excretion in affected dogs, because P-glycoprotein sits in the bile ducts too, so clearance of some drugs falls.

Ivermectin is a substrate for that pump, which is the whole reason the mutation was found at all. A subpopulation of Collies was known to be extremely sensitive to ivermectin-induced neurotoxicity, and the 2001 study set out to find the mechanistic basis; it reported the deletion mutation and showed that homozygous dogs display the ivermectin-sensitive phenotype. The condition was called ivermectin sensitivity for years and was renamed multidrug sensitivity once more drugs were shown to cause neurotoxic signs or other adverse reactions in homozygous animals.

One founder dog, before 1873

Every dog carrying this mutation descends from a single animal, and the date is known to within a few years. A 2004 study in the Proceedings of the National Academy of Sciences used breed phylogeny and reports of drug sensitivity to survey other purebred populations, found the same allele segregating in seven additional breeds including two sighthounds that were not expected to share collie ancestry, and concluded from a conserved mutant haplotype and the extent of linkage disequilibrium that all dogs carrying mdr1-1delta descend from a dog that lived in Great Britain before the genetic isolation of breeds by registry, around 1873. That single origin is why the affected-breed list reads like a family tree. A Hungarian study of 263 client-owned dogs across 17 breeds, published in 2026, found the deletion exclusively in collie-lineage breeds, naming the collie, Shetland sheepdog, Australian shepherd, bobtail and white Swiss shepherd.

The condition is curated by the University of Sydney as OMIA:001402-9615, multidrug resistance 1, ABCB1-related in Canis lupus familiaris, and the record's own reference list runs from the 2001 discovery to a 2026 case of ilunocitinib-induced pancytopenia in an Australian Shepherd with the mutation. Cats have their own version. A nonsense mutation in feline ABCB1 was first identified in 2015 and is present in up to 4 percent of the feline population, and Washington State University puts the figure at around 4 percent of all cats Washington State University, MDR1 testing. The canine test does not detect it, because the two mutations are different.

One copy or two, and where the authorities disagree

To know whether one copy matters, read what your source says and then read its date, because the two named DNA schemes currently give opposite answers. The Royal Kennel Club describes MDR1 as an autosomal-recessive condition and states that a dog which inherits only one copy of the abnormal gene will have no signs of the disease, but will be a carrier. UC Davis lists the mode of inheritance as autosomal incomplete dominance with incomplete penetrance and says some dogs with one copy can also show clinical signs.

Both are respectable sources and both are current. The honest answer is that the field moved and the two pages have not converged, so this page prints the whole spread with dates rather than picking the convenient one.

Read down that column and the disagreement resolves into something usable. It is drug-specific, not global. For ivermectin the original finding has held up well, and heterozygotes mostly tolerate it; for vincristine the evidence runs the other way, and one copy was enough to raise haematologic toxicity significantly in a genotyped, blinded series of 34 dogs with lymphoma. Our page on lymphoma in dogs and cats covers the disease those dogs were being treated for.

Cornell splits the difference in the way a clinician would, saying a dog may be severely affected if it inherits two copies and has only abnormal P-glycoprotein, and that dogs can still experience drug toxicity even with just one copy, though the effects are generally less severe. That is the sentence to carry into the consulting room.

What the breeding arithmetic means for a buyer

Two heterozygous parents produce a quarter affected puppies on average. UC Davis states that a dog with the MDR1/N genotype transmits the variant to 50 percent of its offspring, and that matings between two heterozygous dogs may on average produce 25 percent of puppies who will most likely have a severe form of multidrug sensitivity. Cornell adds the point that gets lost in breeder panic, that because MDR1 drug sensitivity can be easily managed once it is identified, the elimination of all dogs with this variant from a breeding programme is not recommended. Ask a breeder for the parents' genotypes in writing, and treat a refusal as information.

What a reaction looks like, and when to go now

A reaction in an MDR1-affected dog is neurological and it arrives within hours. Cornell lists the most common signs of drug toxicity in these dogs as vomiting, weakness, uncoordinated movement, tremors, seizures, blindness and death. UC Davis adds excess salivation, slow heart rate and dilated pupils, and names respiratory arrest as an endpoint.

Timing separates a drug reaction from most other neurological emergencies. The Indian case reports put the interval at three hours after an oral dose in a pit bull cross at Udgir, twelve hours after an injection in a German Shepherd cross at Rohtak, twelve hours after treatment in a nondescript bitch at Mathura, and four to six hours after injection in six Doberman pups at Izatnagar. If a dog has had any antiparasitic in the last day and then goes wobbly, the two facts belong together.

Recovery is slow and it is usually complete, which is worth knowing before an owner despairs or gives up on treatment. In the largest published series, 17 Collies presented to the University of California veterinary teaching hospital in two groups; the five dogs given the drug orally and presented three hours later showed marked signs, three of them needed mechanical ventilation and were euthanised for financial reasons, and the remaining two were comatose but recovered in five to seven days. Of the twelve dogs in the second group, who were presented two days or five days after a subcutaneous injection, five progressed to stupor or coma and four stayed on their feet, and all twelve survived, though it took three weeks for most of them to recover.

The three deaths in that series were about money

Read the Collie series again with an Indian bill in mind. Fourteen of the 17 dogs lived, and the three that did not were euthanised for financial reasons while on mechanical ventilation, not because the drug had killed them. The authors describe a severe and prolonged clinical course requiring intensive nursing care, with respiratory, cardiovascular and nutritional support all potentially required, and conclude that with appropriate care the prognosis for complete recovery is good. Outcome in this condition tracks what an owner can afford to sustain for a fortnight, which is the strongest practical argument for the cheap test that prevents the admission.

Indian outcomes match that shape where the dogs reached a teaching clinic early. The Udgir pit bull cross recovered, the Mathura bitch recovered over three days of follow-up, the Rohtak German Shepherd cross recovered uneventfully, and the Parbhani dog showed complete recovery by the evening of the third day Jaiswal M, Singh S, Panigrahi PN Sheikh Tajamul Islam, Ganaie MY, Kubra SS Siddiqui MFMF, Sakhare MP, Shafi TA. The exception is the one Indian series with a real denominator. Of six Doberman pups from one litter given the cattle formulation, only two survived, and the authors attribute the four deaths to the injected amount, the delay in presentation and the pups' young age.

The drugs to flag, and the ones that are safe at label amounts

Only one drug on the standard list is an outright never. Washington State University's problem medications table, which includes only drugs that have undergone peer-reviewed publication, records loperamide as causing neurological toxicity in dogs with the MDR1 mutation at the amounts used to treat diarrhoea, and says it should be avoided in all dogs with the mutation. Everything else on the list is a conversation with a prescriber, not a prohibition.

Loperamide matters more in India than the American sources realise, because the brand named on that table, Imodium, sits on Indian pharmacy shelves as a human over-the-counter antidiarrhoeal. Cornell names it as the one drug that should be avoided entirely. A dog with loose motions and a well-meaning owner with a human medicine cabinet is the likeliest domestic route to a reaction that has nothing to do with mange.

The single most useful thing on that table is the pattern rather than any one row. Every modern isoxazoline flea and tick product on it has been tested by its manufacturer in dogs with the mutation, and none showed adverse effects. For an Indian owner whose real problem is ticks and mange, that is the practical exit: a licensed isoxazoline is the route that does not require a genotype first. Our guide to tick prevention for dogs in India covers what is sold here and what it costs.

Same drug, two different amounts, two different outcomes

Ivermectin is safe and dangerous in the same dog, and the variable is the indication. The 2012 review of macrocyclic lactones in MDR1 mutant dogs states the position plainly, that all available macrocyclic lactones can safely be administered to MDR1 mutant dogs at the amounts usually used for heartworm prevention, while these dogs will experience neurological toxicity following the high-amount regimen which is common for mange treatment in dogs. AAHA says the same in one line, that ivermectin and related drugs are safe at the amounts used for heartworm prevention but can become toxic at the amounts used to treat mange. Our page on mange in dogs in India is where that warning matters most, and our guide to heartworm in dogs in India covers the prevention side.

The safe-at-label-amount finding is not a manufacturer's claim, it is a regulatory determination. Mealey's 2008 review of canine ABCB1 and the macrocyclic lactones concludes that at the manufacturer's recommended amount, all FDA-approved heartworm preventive products marketed in the United States are safe even for dogs with the mutant genotype. The 2023 review puts the other end of the range in numbers. For dogs with demodectic mange, extralabel ivermectin given daily at 50 to 100 times the FDA-approved heartworm prevention amount was routinely recommended, and those amounts are often fatal in dogs with P-glycoprotein deficiency unless the patient receives substantial medical care including ventilatory support. So an owner in Pune who has been frightened off monthly heartworm prevention by a blog post has been frightened off the wrong thing.

Two interactions that catch dogs with normal genes too

P-glycoprotein can be knocked out chemically as well as genetically, and that affects any dog. Cornell records that certain medications used in combination can increase the total concentration of individual drugs and introduce more risk of an adverse reaction even in dogs without the genetic variant, naming ketoconazole, cyclosporine and spinosad. The 2023 review makes the same point at the level of mechanism, that P-glycoprotein dysfunction can occur as a result of drug-drug interactions in any dog or cat, and that the concept of inhibitors versus substrates is somewhat arbitrary and artificial. The second interaction is unintentional exposure, and Cornell names the classic route, ivermectin used to deworm horses.

The test, what it costs, and how an Indian owner gets one

To find out whether a dog has the MDR1 gene mutation, have the dog genotyped, because nothing else answers the question. Washington State University states it flatly, that the only way to know if an individual dog has the mutant MDR1 gene is to have the dog tested, and that as more dogs are tested more breeds will probably be added to the list of affected breeds. The sample is a cheek swab or a blood draw, and the laboratory reads one four base pair deletion.

Collection is a job an owner can do at a kitchen table. UC Davis sends cytology brushes by post, asks that the dog has had nothing to eat or drink for at least one hour, and wants the bristle head worked between the gums and cheek for 15 seconds, air-dried for 20 seconds and returned unsealed, with three brushes per dog in most cases. Puppies should be at least three weeks old and must be kept away from the mother, littermates and shared toys for an hour first, because the mother's genetic material can rub off on the puppy's mouth and contaminate the sample.

Cheap is not the same as useful, and Washington State University says so about its competitors in its own price page. It warns that pet owners should read the fine print before having a pet tested by just any company, because many companies specifically state that their results are not intended to be used as the basis of a medical diagnosis or treatment, so while less expensive they are not useful medically. That sentence is the one to hold on to before buying an imported consumer breed-and-health kit through an Indian marketplace. The founding researcher's own warning on the same laboratory's testing page is blunter, that this can be a life-or-death condition and an incorrectly genotyped animal treated with one of the problem drugs can be killed by it.

Reading the result

A result comes back as one of three genotypes and each one means something different at the prescribing pad. UC Davis reports N/N as normal, MDR1/N as one copy detected with clinical signs that could be mild, and MDR1/MDR1 as affected and likely to show severe multidrug sensitivity. The laboratory's own explanation adds that an MDR1/MDR1 dog is likely to show severe signs even at low amounts of a substrate drug.

What the test does not tell you

The standard MDR1 test reads one variant and is blind to three other things, which no ranking page mentions. UC Davis states that the test does not detect a different variant in ABCB1 that has been associated with phenobarbital-resistant epilepsy in the Border Collie, that it is specific to dogs and will not detect the feline variant, and that drug sensitivity may also be caused by other less common variants in ABCB1 or other genes, or by drugs that inhibit P-glycoprotein and produce a reversible, non-genetic form. The Border Collie variant is not rare. A survey of 472 Border Collies in Japan found the c.-6-180T>G genotypes at 60.0 percent T/T, 30.3 percent T/G and 9.8 percent G/G, a mutant G allele frequency of 24.9 percent. Our page on epilepsy in dogs covers the seizure side of that finding.

A 2026 Hungarian study found the two variants travelling together. Across 263 client-owned dogs from 17 breeds, the G allele of c.-6-180T>G ran at 35 percent overall with 111 T/T, 119 T/G and 33 G/G dogs, and every individual carrying the four base pair deletion also carried at least one G allele, which the authors read as shared ancestry or local linkage disequilibrium.

Getting it done from India

No Indian laboratory was found offering the ABCB1 test, so the sample travels. The route below is what the two laboratories' own instructions describe, and the arrangements for an international sample are a question for the laboratory and for a veterinarian in India, not something this page can settle.

1. Ask the veterinarian whether the dog's breed, ancestry or planned treatment makes the genotype worth knowing at all.
2. Order the collection kit directly from the laboratory's own site rather than from a marketplace reseller, so the fine print on medical use is the laboratory's.
3. Collect the cheek sample to the laboratory's written protocol, with the dog fasted for an hour and the brush worked against the gum rather than the tongue or teeth.
4. Budget the converted price, roughly Rs 4,300 to Rs 5,900 for a single test before any courier charge, and treat that as a dollar price that moves with the exchange rate.
5. Put the printed genotype in the dog's file and give a copy to every clinic that treats the dog, because a result nobody can find has bought nothing.

For a dog registered with a kennel body there is a second reason to test through a recognised laboratory. The Royal Kennel Club runs MDR1 as one of its official DNA testing schemes, records results only from laboratories that meet its criteria, and publishes them on a Health Test Results Finder that anyone choosing a mate can search. A result from a laboratory outside that list is not recorded.

What the breed percentages actually mean

Read any MDR1 breed percentage twice, because two different quantities are printed under the same heading. Washington State University's table gives an approximate frequency for the breed, with Collie at 70 percent, Australian Shepherd at 50 percent, German Shepherd at 10 percent and Border Collie at under 5 percent. Most of the peer-reviewed surveys behind those rows report the mutant ALLELE frequency, which counts copies rather than dogs and is a smaller number for the same population.

The gap is not academic. Germany's 7,378-dog screen reports a mutant allele frequency of 59 percent in Collies, while Washington State's table reports 70 percent for the breed Washington State University. Those two numbers are not in conflict, because they are not the same measurement, and every page that prints them side by side without saying so is confusing its reader.

The hundredfold correction nobody prints

The famous breed percentages come from a self-selected pool, and one study measured how much that inflates them. Ghent University genotyped 286 random residual blood samples from a small animal clinic, a cohort of 90 different breeds and mixes in which mixed breeds were the largest group and German shepherds, Labrador retrievers, golden retrievers and chihuahuas completed the top five. Exactly one of the 286 was heterozygous, a Shetland sheepdog, giving an allele frequency of 0.2 percent with a 95 percent confidence interval of 0 to 0.52 percent.

The comparison population came from the same region and the same laboratory. Among 599 samples sent in specifically for genetic testing the allele frequency was 21.6 percent, roughly 100 times higher than the clinic figure, and the authors conclude that the risk of overestimating allele frequency from commercial tests can be up to 100 times greater. Under Hardy-Weinberg assumptions the clinic figure predicts 0.0003 percent homozygous and 0.35 percent heterozygous dogs in that population. The authors still end up endorsing the screening rule, because the one carrier they found was in a breed already known to be at risk, so prioritising at-risk breeds before treatment seems justified.

Where the laboratory's own table and its authors' review disagree

Two figures published by the same university differ, and the difference is not small. Washington State's public breed table gives the Long-haired Whippet at 50 percent, while Table 1 of the 2023 review written by the laboratory's own founder gives the Longhaired whippet at 65 percent, the figure AAHA also reproduces Mealey KL, Owens JG American Animal Hospital Association…. The mixed-breed row moves the same way, at 5 percent on the table and up to 10 percent in AAHA's account American Animal Hospital Association…. The review is also less cautious than the table about the newest breeds, printing Black Mouth Cur at 8 of 26 dogs tested and Chinook and Carolina Dog at 4 of 13 each where the public table says Black Mouth Cur and Carolina have not had enough dogs tested to calculate. Two rows in that review are worth an owner's attention for the opposite reason, because the Boxer and the Siberian Husky appear at under 1 percent, each confirmed purebred by pedigree and DNA breed analysis.

The breed list is a starting point and the laboratories say so themselves. Washington State records the mutant gene in a Saint Bernard mix that had an adverse drug reaction, noted because the dog's eyes were different colours like some Australian shepherds. AAHA goes further, warning that even dogs which do not obviously look like herding-breed mixes can be homozygous, and that it may be prudent to discuss testing with owners of all mixed-breed dogs before giving a P-glycoprotein substrate. For India, where most dogs are indies and mixes of unknown ancestry, that is the sentence that actually applies.

MDR1 in India: cheap ivermectin, no Indian data, and the German Shepherd question

In India the MDR1 gene is not the main way dogs get poisoned by ivermectin, and saying otherwise misdirects the reader. Every published Indian case of canine ivermectin toxicosis on the record began with an owner giving the drug at home, and not one of the dogs involved was a Collie Jaiswal M, Singh S, Panigrahi PN Sheikh Tajamul Islam, Ganaie MY, Kubra SS Siddiqui MFMF, Sakhare MP, Shafi TA Sharma A, Singh KP, Khurana KL. The Indian harm on the record is plain overdose in ordinary dogs.

Five Indian veterinary reports describe it, from four states. A two-year-old American Pit Bull Terrier crossbred bitch at the teaching clinic in Udgir, Maharashtra, was admitted in lateral recumbency three hours after an oral ivermectin tablet given by her owner for ticks, and recovered. A ten-year-old nondescript bitch at DUVASU in Mathura, Uttar Pradesh, went apparently blind twelve hours after owner treatment for ticks and recovered over three days. A one-year-old German Shepherd cross at IIVER in Rohtak, Haryana, showed ataxia, partial blindness and a dilated pupil twelve hours after an owner-given injection, and recovered uneventfully. A nine-year-old nondescript male dog at MAFSU in Parbhani, Maharashtra, was given a bolus around 14 times the amount his weight called for, went blind and hypothermic, and recovered fully by the evening of the third day.

The fifth is the only Indian report with a real denominator and it is the worst of them. Six Doberman pinscher pups from one litter were presented to the Referral Veterinary Polyclinic at the Indian Veterinary Research Institute in Izatnagar, Bareilly, Uttar Pradesh, after their owner injected them with the ivermectin product used in cattle; the pups went into severe depression, recumbency and blindness within four to six hours, and only two of the six survived. The paper reports the overdose two ways, as 50 times the amount recommended for dogs as an antiparasitic in its abstract and as more than 1,600 times the heartworm-prevention amount in its discussion, and both are arithmetically right against the two different reference points it names.

One bottle, five species

The reason a cattle product ends up in a puppy is on the label. The IVRI authors write that it is unfortunate that in India the same product is indicated for a number of species of animals, naming cows, buffaloes, sheep, goat and dogs, and note that the solvent glycerol formal used in the cattle and buffalo preparation can itself account for some of the toxicity seen. They also record that ivermectin has been used extensively in dogs in India for the last 20 years despite its only registered indication in dogs being heartworm. The Udgir authors name the mechanism without hedging, that the slight overdosing of anthelmintics with a narrow margin of safety, or the use of drugs without a valid veterinarian's prescription by animal owners, may lead to cases of toxicity.

Season is part of the exposure. Mite and tick pressure climbs through the monsoon and stays high year round in the humid coastal cities, which is when the ivermectin comes off the shelf, and the Rohtak and Mathura owners were both treating ticks rather than mange when their dogs were poisoned Jaiswal M, Singh S, Panigrahi PN. Our page on mange in dogs in India carries the Indian prevalence figures for the disease those owners were trying to treat.

The finding that reframes all of it

Most dogs that fall neurologically ill on mange-amount macrocyclic lactone treatment do not have the mutation. Cheek swabs were taken from 28 dogs of non-collie breeds that had shown subchronic signs of neurotoxicity following daily oral ivermectin or another systemic macrocyclic lactone for generalized demodicosis, and the ABCB1 region was amplified and sequenced; 27 were homozygous normal and one was heterozygous. The authors conclude that with the exception of one dog the observed neurotoxicity could not be attributed to the mutation, and list the likelier explanations, including pharmacological interactions with other P-glycoprotein substrates or inhibitors and excessively high amounts. For an Indian reader that is the whole point. Testing the dog is worth doing where the breed warrants it, and it will not protect a dog from a cattle syringe.

The German Shepherd question

The German Shepherd is India's commonest large pedigree and its 10 percent figure has a narrow provenance. Washington State's table lists German Shepherd at 10 percent and the 2023 review repeats it Mealey KL, Owens JG, but the finding originates in a North American genotyping pool of 5,368 dogs where the allele was reported in the German Shepherd Dog for the first time. Outside North America the picture is different. Israel's 1,416-dog survey found an allele frequency of 2.4 percent in 21 pure German Shepherds, and describes itself as the first evidence of the mutation in the breed outside the United States, at frequencies of roughly 2.5 to 4 percent. Thailand found it in none of 20 German Shepherds and noted that its German Shepherds were predominantly of German lines with only a very small proportion descended from the American line. Germany's own 7,378-dog screen does not list the German Shepherd among the breeds where the mutation was found, and Hungary's 2026 study found the deletion exclusively in collie-lineage breeds.

Nobody has genotyped an Indian German Shepherd, so the honest answer is a range with a gap in the middle. The figure an Indian owner is shown, 10 percent, is measured in dogs from a different continent with different breeding lines, and the two nearest Asian measurements are zero of 20 in Thailand and one dog in 21 in Israel Dekel Y, Machluf Y, Stoler A, Aderet. That does not make the test pointless for a German Shepherd in Delhi or Hyderabad, because a single carrier is still a carrier, and it does mean nobody should quote 10 percent as an Indian number.

The Indian absence, and how it was checked

No Indian dog appears in the published MDR1 genotype literature, and that absence was tested rather than assumed. A Europe PMC search on 27 September 2026 for MDR1 or ABCB1 with a canine term and either India in the title and abstract or India in the author affiliation returned three records, and all three were artefacts: a preclinical tissue-distribution study of a cancer drug, a drug-transport study in MDCKII-MDR1 cell lines, and a multi-drug-resistance oncology paper, none of them about dogs carrying the canine variant. The equivalent search for Indian canine ivermectin toxicity returned zero in the title and abstract and, on affiliation, 16 records of which exactly one was a dog paper, the IVRI Doberman series Sharma A, Singh KP, Khurana KL. The other 15 covered malaria vectors, carp, a rabbit eye model, tick resistance in Punjab and several in-silico screens. Two controls run through the identical instrument in the same session passed, returning 49 records for Labrador retriever hip dysplasia and 39 for canine parvovirus in India.

Geography narrows it further. The five Indian reports come from Maharashtra, Uttar Pradesh and Haryana, and all five were written at inland teaching clinics Jaiswal M, Singh S, Panigrahi PN Sheikh Tajamul Islam, Ganaie MY, Kubra SS Siddiqui MFMF, Sakhare MP, Shafi TA Sharma A, Singh KP, Khurana KL. Nothing has been published from Mumbai, Bengaluru, Chennai, Kolkata or Pune, and neither Tamil Nadu nor Karnataka appears anywhere in the Indian literature on this drug, which is where a large share of the country's pedigree dogs live. A reader in a coastal metro is working from an inland, small-town evidence base and should treat it as the closest available signal rather than a local measurement.

What the Indian page that ranks gets wrong

The Indian page ranking on this query gives advice that the genotyped evidence contradicts. VOSD's ivermectin article, medically reviewed and last modified on 8 June 2026, tells readers that in MDR1-positive dogs milbemycin oxime is generally considered safer because it does not cross the blood-brain barrier as readily. The study that genotyped dogs and tested exactly that found otherwise. Twenty-two dogs with generalized demodicosis were treated with milbemycin oxime, 15 of them herding breeds; none of the 19 dogs with the wild-type allele had an adverse reaction, and two dogs homozygous for the mutation developed ataxia, a statistically significant association. The authors conclude that assessing the genotype before giving milbemycin oxime may prevent neurological toxicity. The same page also uses the phrase MDR1 positive throughout, which the laboratory that invented the test asks people to stop using Washington State University, MDR1 testing.

Living with a dog that carries it

A dog with the mutation lives an ordinary life, and the management is administrative rather than medical. Cornell states that with proper consideration of drug interactions and dosages, MDR1 drug-sensitive dogs can live normal lives without incident, and that severe consequences follow when drugs are given at incorrect amounts, in certain combinations, or by accidental exposure. Nothing about the dog needs changing. The record that travels with the dog does.

The genotype is only useful when the person holding a syringe can see it. UC Davis puts this in its testing recommendations, that results should be shared with the dog's veterinarian before pharmacological treatments, and that is a harder ask in India than in the countries those pages were written for, where one practice holds one lifetime record. A dog in Mumbai or Kolkata may see a housing-society vet, a night emergency clinic and a travelling groomer in the same month.

• Keep the printed genotype, not a screenshot of a summary, because the laboratory's own report is the document a clinic will accept.
• Say the genotype out loud at every new clinic, before consent is given for sedation, worming or anaesthesia.
• Name the drug class, not the brand, when asking whether something is safe, because the same molecule is sold under several Indian names.
• Keep human antidiarrhoeals away from the dog entirely, since loperamide is the one drug the laboratory says to avoid in all dogs with the mutation.
• Ask before a cancer protocol starts, because heterozygous as well as homozygous dogs were significantly more likely to develop neutropenia and thrombocytopenia after vincristine.

The adrenal finding almost nobody mentions

The mutation does something beyond drug handling, and it matters when the dog is seriously ill. Washington State records that the MDR1 mutation is associated with a blunted hypothalamic-pituitary-adrenal axis, so affected dogs are especially prone to relative adrenal insufficiency when they are seriously ill, and that they benefit from physiologic corticosteroid support. The 2008 breed-distribution paper flags the same association in its clinical relevance statement. A dog in intensive care in Chennai or Bengaluru for something unrelated to any drug is still a dog whose genotype is worth knowing.

What to do if a dose has already gone in

Speed and information are the two things an owner controls. There is no antidote for ivermectin toxicity, and the Indian reports are unanimous that management is symptomatic and supportive Sheikh Tajamul Islam, Ganaie MY, Kubra SS. The Parbhani authors close their report with the practical conclusion, that ivermectin toxicity in a dog occurs through owner negligence but it is possible to save the life of the affected dog and complete recovery can occur if treatment is given on time and properly, even though there is no specific antidote.

1. Take the packet, strip or bottle with you, so the clinic can read the formulation and the species it was made for.
2. Tell the clinic when the dose went in, because the Indian reports put the onset between three and twelve hours and that interval shapes the plan Sheikh Tajamul Islam, Ganaie MY, Kubra SS.
3. Say whether the dog has ever been genotyped, and hand over the printed result if it has.
4. Expect a long recovery rather than a quick one, since most of the Collies in the published series took days to weeks and the group presented late took about three weeks.

Breeding decisions follow the same logic and the same restraint. Test before breeding, because two heterozygous parents give each puppy a 25 percent chance of two copies and a 50 percent chance of one, and do not cull the line over it, because the condition is easily managed once identified and removing every carrier from a programme is not recommended. Our breed pages for the Rough Collie and the German Shepherd carry the rest of each breed's health picture, and our dog deworming schedule for India covers the routine parasite control this genotype touches most often.