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Mdr1 Gene Defect (Ivermectin Sensitivity) in Dogs

Occurrence: rarer
Location of illness: General/Whole body

Author: Dr. med. vet. Gisa Löwe | Last modified: 06.11.2025

The mdr1 gene defect, also known as ivermectin sensitivity, is a genetic mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits. in dogs that leads to increased sensitivity to certain medications, especially those that affect the central nervous systemThe CNS (central nervous system) consists of the brain and spinal cord. It is responsible for processing information and controls most functions of the body and behavior..

The most important facts at a glance

The mdr1 gene defect affects the MDR1 gene, which is responsible for P-glycoprotein, an important proteinProteins are large molecules made up of amino acids and play an essential role in almost all biological processes. They are necessary for building body tissue, the function of the immune system, and as enzymes for metabolic reactions. for protecting the brain. In dogs with this genetic defectA genetic defect is an abnormality or mutation in the DNA sequence of a gene that can lead to a malfunction or absence of a protein. Genetic defects can cause various genetic diseases and conditions., the function of the protein is impaired, which can lead to certain drugs entering the brain in toxicToxic means "poisonous" and refers to substances that can have harmful effects on the body, including damage to organs, cells, or disruption of metabolic processes. amounts. This can lead to serious neurological symptoms. The mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits. is autosomal recessive; affected dogs must have two copies of the defective gene. The defect is particularly common in breeds such as Collies and Australian Shepherds. Symptoms can range from disorientation and tremors to seizures. DiagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. is made by genetic tests that confirm the presence of the mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits.. Treatment consists mainly of avoiding problematic drugs. If a dog is nevertheless exposed to such a drug, immediate veterinary treatment is necessary. The prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. for affected dogs is good if the problematic drugs are avoided. PreventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. begins with genetic testing in breeding animals to reduce the spread of the mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits.. Research focuses on the spread of the defect and the development of safe treatment strategies, as well as on understanding the genetic basis of the defect.

Causes

The mdr1 gene defect affects the MDR1 gene (Multidrug ResistanceResistance refers to the ability of microorganisms to withstand the effects of antibiotics, antifungals, or other antimicrobial drugs. Resistance can also refer to the body's ability to be insensitive to diseases or toxins. Gene 1), which is responsible for producing a proteinProteins are large molecules made up of amino acids and play an essential role in almost all biological processes. They are necessary for building body tissue, the function of the immune system, and as enzymes for metabolic reactions. called P-glycoprotein. This proteinProteins are large molecules made up of amino acids and play an essential role in almost all biological processes. They are necessary for building body tissue, the function of the immune system, and as enzymes for metabolic reactions. plays a crucial role in protecting the brain by regulating the transport of certain substances across the blood-brain barrierThe blood-brain barrier is a protective barrier between the blood vessels in the brain and the brain tissue. It prevents most substances in the bloodstream from entering the brain tissue, but allows nutrients and oxygen to pass through.. In dogs with this mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits., the function of this proteinProteins are large molecules made up of amino acids and play an essential role in almost all biological processes. They are necessary for building body tissue, the function of the immune system, and as enzymes for metabolic reactions. is impaired.

The absence or malfunction of P-glycoprotein allows certain drugs, which are normally kept out of the brain, to enter in toxicToxic means "poisonous" and refers to substances that can have harmful effects on the body, including damage to organs, cells, or disruption of metabolic processes. concentrations. This can lead to serious neurological symptoms. The mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits. is autosomal recessive, meaning that dogs must carry two copies of the defective gene to be affected.

The cause of the mdr1 gene defect is genetic. Certain dog breeds are predisposed, including Collies, Australian Shepherds, Shetland Sheepdogs, and others. The mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits. is likely due to a common ancestor, and its prevalence in certain breeds suggests a selective breeding practice that has unintentionally passed on the defective gene.

Symptoms

Common symptoms:

Rare symptoms:

Dogs with the mdr1 gene defect show symptoms when exposed to certain medications. The most common symptoms include neurological signs such as tremors, convulsions, ataxia (Coordination disorders), lethargy, and in severe cases, comaA coma is a deep state of unconsciousness where an individual cannot be awakened and does not respond to stimuli. In dogs and cats, it can be caused by severe illnesses, poisoning, or neurological problems.. These symptoms are due to the toxic effects of the drugs on the central nervous systemThe CNS (central nervous system) consists of the brain and spinal cord. It is responsible for processing information and controls most functions of the body and behavior..

The severity of the symptoms can vary, depending on the dose of the drug, the size of the dog, and the degree of gene mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits.. In some cases, gastrointestinalGastrointestinal refers to the gastrointestinal tract, a system that extends from the oral cavity to the anus and is responsible for the digestion of food and the absorption of nutrients. symptoms such as vomiting and diarrheaDiarrhea refers to the condition of frequent, watery bowel movements, which can be a sign of infections, digestive disorders, or other health problems. may also occur, indicating a systemic reaction of the body.

Diagnosis

The diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. of an mdr1 gene defect is usually made by a genetic test. A simple cheek swab or blood sample can be used to analyze the MDR1 gene. The test determines whether the dog is a carrier of the defective gene or whether it actually has two copies of the mutated gene, making it susceptible to the symptoms.

In addition to genetic testing, the veterinarian can also make a clinical diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. based on the dog’s historyThe medical history is the systematic collection of a patient's medical history through questioning. It includes information about previous illnesses, treatments, allergies, and lifestyle habits., symptoms, and response to certain medications. If a dog shows symptoms after administration of a known problematic drug, this may be a strong indicationIndication refers to a valid reason or rationale for using a specific treatment, medication, or medical procedure. It is based on the diagnosis and the patient's clinical condition. of an mdr1 gene defect.

Therapy

The treatment of dogs with mdr1 gene defect consists primarily of avoiding the administration of the problematic drugs. If a dog is accidentally exposed to one of these drugs, immediate veterinary treatment may be necessary to alleviate the symptoms and prevent complications. This may include the administration of activated charcoalActivated charcoal is a fine-pored, highly adsorbing material commonly used in veterinary medicine to treat poisoning. It binds toxins in the gastrointestinal tract to prevent their absorption into the body. to reduce the absorptionAbsorption refers to the uptake of substances by living cells or tissues. In the context of veterinary medicine, it often refers to the absorption of nutrients, drugs, or toxins from the digestive tract into the bloodstream. of the drug or the administration of medications to control convulsions.

In the long term, it is important that pet owners and veterinarians are aware of which medications should be avoided in affected dogs. These include ivermectin, some antiparasiticsAntiparasitics are medications or substances used to treat parasitic infestations, such as worms, protozoa, and ectoparasites. They work by killing the parasites or inhibiting their growth., certain antibiotics, and pain relievers. Close cooperation with the veterinarian is crucial to find alternative medications that are safe for the dog.

Prognosis and follow-up care

The prognosis for dogs with an mdr1 gene defect is generally good as long as the problematic drugs are avoided. Dogs can live a normal, healthy life if they are properly monitored and treated. In cases where a dog is accidentally exposed to a problematic drug, the prognosis depends on the prompt treatment and the severity of the symptoms.

It is important to note that the mdr1 gene defect is a lifelong condition that requires continuous monitoring. However, with the right precautions and care, most dogs can live without major restrictions.

Prevention

The preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. of the mdr1 gene defect begins with genetic testing of breeding animals. By identifying and eliminating carriers of the defective gene from the breeding pool, the spread of the mutation in future generations can be reduced. This requires careful breeding practice and cooperation between breeders, veterinarians, and geneticists.

For dogs that are already affected by the mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits., the best preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. is to avoid medications that can cause negative reactions. Pet owners should be well informed and ensure that all medical caregivers of the dog are informed about the animal’s mdr1 status. Regular veterinary check-ups and cooperation with an experienced veterinarian can help minimize the risk of undesirable drug effects.

For more information and research on this topic, please visit the [American Veterinary Medical Association](https://www.avma.org) and the [Washington State University Veterinary Clinical Pharmacology Laboratory](https://vcpl.vetmed.wsu.edu).

Outlook on current research

The MDR1 gene defect, also known as ivermectin sensitivity, is a genetic condition in dogs that has received increased attention in scientific research in recent years. This defect affects the Multidrug ResistanceResistance refers to the ability of microorganisms to withstand the effects of antibiotics, antifungals, or other antimicrobial drugs. Resistance can also refer to the body's ability to be insensitive to diseases or toxins. Gene (MDR1), which is responsible for producing a protein known as P-glycoprotein. This protein plays a crucial role in protecting the brain from potentially toxicToxic means "poisonous" and refers to substances that can have harmful effects on the body, including damage to organs, cells, or disruption of metabolic processes. substances by actively pumping them out of the cells. Dogs with an MDR1 gene defect do not produce enough of this proteinProteins are large molecules made up of amino acids and play an essential role in almost all biological processes. They are necessary for building body tissue, the function of the immune system, and as enzymes for metabolic reactions., making them more sensitive to certain medications, including ivermectin, a commonly used dewormer.

Research is currently focused on identifying the prevalence of the MDR1 defect in various dog breeds. Studies have shown that the defect is particularly common in Collies, Australian Shepherds, Shetland Sheepdogs, and other herding breeds. Genetic tests are now widely available, allowing veterinarians and owners to determine the presence of the defect in a dog before certain medications are administered. This helps to minimize the risk of serious side effects.

Another focus of current research is the development of safe treatment strategies for dogs with the MDR1 gene defect. Scientists are investigating alternative medications and dosage adjustments to ensure that affected dogs can be treated effectively and safely. In addition, studies are being conducted to better understand the molecular mechanisms underlying drug sensitivity. These findings could lead to the development of new therapeutic approaches in the long term that are specifically tailored to dogs with the MDR1 defect.

Research into the geneticsGenetics is the science of genes, heredity, and the variation of organisms. It studies how genetic information is passed from generation to generation and how it influences the development, appearance, and behavior of living things. of the MDR1 defect is also ongoing. Scientists are working to map the genetic variations and mutations that lead to this defect. This knowledge could contribute to the breeding of dogs that are free of the defect, which supports the long-term goal of the breeding community to reduce the prevalence of the MDR1 defect. Genetic research has already made significant progress, but further studies are needed to fully understand the complexity of this genetic problem.

In addition to genetic and pharmacological studies, scientists are also investigating the effects of the MDR1 defect on the behavior and quality of life of affected dogs. Some studies suggest that the defect may not only affect drug sensitivity but may also cause subtle changes in behavior or neurological function. This research is still in its early stages, but it could provide valuable information about how comprehensively the MDR1 defect actually affects the life of an affected dog.

Frequently asked questions (FAQs)

What is the MDR1 gene defect in dogs? The MDR1 gene defect is a genetic mutationA mutation is a permanent change in the DNA sequence (genetic material) of an organism. In dogs and cats, mutations can lead to genetic diseases or desirable changes in certain traits. that impairs the production of P-glycoprotein, which serves to remove harmful substances from the brain. Dogs with this defect are sensitive to certain medications, such as ivermectin.
Which breeds are most commonly affected by the MDR1 defect? The MDR1 defect is particularly common in Collies, Australian Shepherds, Shetland Sheepdogs, and other herding breeds. Other breeds may also be affected, but less frequently.
How can I tell if a dog has the MDR1 defect? There are genetic tests that can be performed by veterinarians to determine if a dog is a carrier of the MDR1 defect. These tests are simple and reliable.
Which medications are dangerous for dogs with the MDR1 defect? Dogs with the MDR1 defect are sensitive to several medications, including ivermectin, loperamide, and some cancerCancer refers to the uncontrolled proliferation of cells that can lead to tumors or spread throughout the body. Various types of cancer occur in dogs and cats, ranging from skin cancer to lymphomas. medications. It is important to talk to your veterinarian about the safe use of medications.
What symptoms occur with drug hypersensitivity? Symptoms of hypersensitivity can include vomiting, diarrheaDiarrhea refers to the condition of frequent, watery bowel movements, which can be a sign of infections, digestive disorders, or other health problems., tremors, convulsions, and in severe cases, comaA coma is a deep state of unconsciousness where an individual cannot be awakened and does not respond to stimuli. In dogs and cats, it can be caused by severe illnesses, poisoning, or neurological problems.. A veterinarian should be consulted immediately if a reaction is suspected.
Can the MDR1 gene defect be cured? The MDR1 gene defect cannot be cured because it is genetic. Treatment focuses on avoiding contact with problematic medications.
Are there alternative treatments for dogs with the MDR1 defect? Yes, there are alternative medications and treatment strategies that are safer for dogs with the MDR1 defect. Your veterinarian can recommend appropriate options.
How can I prevent my dog from passing on the MDR1 defect? If your dog is a carrier of the MDR1 defect, you should carefully consider breeding and ensure that the partner dog is free of the defect. Genetic testing before breeding is advisable.
Does the MDR1 defect affect my dog’s behavior? Currently, there is no reliable evidence that the MDR1 defect directly affects behavior. However, research in this area is ongoing.
How can I reduce the MDR1 defect in the dog populationIn veterinary medicine, the term population refers to a group of animals of a particular species living in a specific geographic area or environment.? Responsible breeding practices and genetic testing are key to reducing the spread of the MDR1 defect. Awareness and education among dog owners and breeders are also important.