What is MDR1?
     Australian Shepherds, along with several other mostly collie-type breeds, can carry a genetic mutation that makes them sensitive to certain drugs. Use of those drugs can cause serious neurological illness or death.
     There is a DNA test that will let you know whether your dog has this mutation. All you have to do is provide a cheek swab. It isn’t even necessary to go to the vet. However many breeders and vets alike have found this test not not be accurate. Dogs tested Clear that should have no reaction do. Dogs tested affected by MDR1, sometimes have no reaction.
What is MDR1?
MDR1 is the abbreviated name of a gene called Multi-Drug Resistance 1.
A mutation of this gene causes sensitivity to Ivermectin and a number of other drugs. Dogs with the mutation will react to those drugs. Whether a dog reacts depends on the dosage of the drug.
A dog may not react to very low doses, as with the amount of Ivermectin found in heart worm products. Typical doses of a variety of medications will cause reactions in dogs with two copies of the mutation, but some drugs – most notably several chemotherapy agents – can cause reactions in dogs with only one. Dogs with this mutation have a transport defect—the drug goes in to their brains, fails to be transported out, and builds up to toxic levels. This causes serious neurological problems including seizures and sometimes death.
Which drugs cause MDR1 reactions?
Ivermectin was the first drug recognized to cause a reaction, but it is far from the only one. Ivermectin at low dosage, as found in heartworm medications, will not cause a reaction. The larger doses needed for worming will. Other commonly administered drugs on the list include acepromazine and Imodium. Fortunately, there are alternative medications available if your dog requires treatment.
THE ONLY SAFE WAY IS TO TREAT ALL AUSSIES AS AFFECTED and avoid these drugs at all cost!
Yes, this will mean standing your ground with your Vet, as you are you dogs BEST advocate.
*We do administer and advocate the use of heartworm medication, but we allow as much time between it and any other drugs so as to accommodate observation for any sort of reaction. Example: flea/tick prevention administered on the 1st of the month = heart worm prevention administered the 14th of the same month (14 days apart)