Invermectin Sensitivity MDR1 (Multi Drug Resistance)
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.
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.
Some testing labs refer to having one copy of MDR1 or other genes as having “carrier” status. This is only accurate if the gene mutation in question is recessive. That is not the case with MDR1, which is incompletely dominant. Dogs with one copy are affected, though to a lesser degree. They will react to every drug on the list if the dosage is high enough.
What this means is both Affected and Carrier DNA status should be treated as affected by the gene.
Below is a link to problem drugs
https://vcpl.vetmed.wsu.edu/problem-drugs
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.
Some testing labs refer to having one copy of MDR1 or other genes as having “carrier” status. This is only accurate if the gene mutation in question is recessive. That is not the case with MDR1, which is incompletely dominant. Dogs with one copy are affected, though to a lesser degree. They will react to every drug on the list if the dosage is high enough.
What this means is both Affected and Carrier DNA status should be treated as affected by the gene.
Below is a link to problem drugs
https://vcpl.vetmed.wsu.edu/problem-drugs
