MDR1 DNA Test for Drug Intolerance in Dogs

A mutation in the ABCB1 gene leads to increased sensitivity (multidrug resistance, MDR) to certain medications and can cause severe poisoning in affected dogs. With the genetic test for multi-drug resistance 1 (MDR1), you can determine whether your dog is a carrier of the ABCB1 gene mutation that causes this condition. The defect is considered to be autosomal recessive, but even heterozygous animals show increased sensitivity to certain medications.

What is the MDR1 gene defect?

Dogs with an MDR1 gene defect experience increased transfer of certain drugs into the central nervous system. This causes drugs such as ivermectin, doramectin, moxidectin, or loperamide to accumulate and have a neurotoxic effect. This results in severe symptoms of poisoning after administration of these drugs. The effectiveness of other medications may also be limited by the defect.

Symptoms of the MDR1 gene defect:

• Symptoms of poisoning (tremors, coordination problems, vomiting, convulsions) after taking certain medications.

• Lack of effectiveness of medications.

   

Why is a genetic test important?

A simple MDR1 genetic test can provide clarity as to whether your dog is affected by this genetic disorder. With this knowledge, you and your veterinarian can adjust the medication dosage precisely and minimize the risk of unwanted side effects. The test is a valuable preventive measure, especially for breeds in which the genetic defect responsible for MDR1 is common.

For which dogs is the test particularly important?

Collies, Shetland Sheepdogs, Australian Shepherds, Miniature American Shepherds, and White Swiss Shepherds are particularly affected. In other breeds, the incidence is rather low and is due to crossbreeding with the at-risk breeds. Mixed breeds of these breeds may also carry the defect.

Advantages of the MDR1 gene test:

• Ensures safe administration of medication
• Prevents serious poisoning
• Identifies undetected carrier animals for effective breeding planning

More Information

Publication: Ivermectin sensitivity in collies is associated with a deletion mutation of the mdr1 gene (2001) Mealey, K. L. et al.  10.1097/00008571-200111000-00012

Lexicon: Multi Drug Resistance (MDR1 Hund) 

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