MDR-1 Sensitivity

Many herding breed dogs have a genetic predisposition to adverse drug reactions involving over a dozen different drugs.  As long as these drugs are not administered or under supervision in controlled amounts, your collie can live a long and healthy life.

The most serious adverse drug reactions involve several antiparasitic agents (ivermectin, milbemycin and related drugs), the antidiarrheal agent loperamide (Imodium), and several anticancer drugs (vincristine, doxorubicin, others). These drug sensitivities result from a mutation in the multidrug resistance gene (MDR1 gene).

A list of drugs that are known to cause problems

  • Acepromazine (tranquilizer and pre-anesthetic agent). In dogs with the MDR1 mutation, acepromazine tends to cause more profound and prolonged sedation.
  • Butorphanol (analgesic and pre-anesthetic agent). Similar to acepromazine, butorphanol tends to cause more profound and prolonged sedation in dogs with the MDR1 mutation.
  • Emodepside (Profender�)-is a deworming drug approved for use in cats only in the U.S., but is approved for use in dogs in some other countries.  Use of this drug in dogs with the MDR1 mutation has resulted in neurological toxicity.
  • Erythromycin. Erythromycin may cause neurological signs in dogs with the MDR1 mutation.  A mutant/mutant collie exhibited signs of neurological toxicity after receiving erythromycin.  After withdrawal of the drug, the dogs neurological signs resolved.  There were no other potential causes of neurological toxicity identified in the dog.
  • Ivermectin (antiparasitic agent). While the dose of ivermectin used to prevent heartworm infection is SAFE in dogs with the mutation (6 micrograms per kilogram), higher doses, such as those used for treating mange (300-600 micrograms per kilogram) will cause neurological toxicity in dogs that are homozygous for the MDR1 mutation (mutant/mutant) and can cause toxicity in dogs that are heterozygous for the mutation (mutant/normal).
  • Loperamide (ImodiumTM; antidiarrheal agent). At doses used to treat diarrhea, this drug will cause neurological toxicity in dogs with the MDR1 mutation.
  • Selamectinmilbemycin, and moxidectin (antaparasitic agents). Similar to ivermectin, these drugs are safe in dogs with the mutation if used for heartworm prevention at the manufacturer’s recommended dose.  Higher doses (generally 10-20 times higher than the heartworm prevention dose) have been documented to cause neurological toxicity in dogs with the MDR1 mutation.
  • Vincristine, Vinblastine, Doxorubicin (chemotherapy agents). Based on some published and ongoing research, it appears that dogs with the MDR1 mutation are more sensitive to these drugs with regard to their likelihood of having an adverse drug reaction.

Make sure you and your vet have this list!