As a rule the Collie is a healthy/hardy breed. However, the Collie, like all breeds of dogs, has certain health issues. Collie Eye Anomaly (CEA) is an inherited eye disease that is present at birth. About 80 percent of Collies have a genetic predisposition, resulting from a mutation in the multidrug resistance gene (MDR1 gene), to adverse drug reactions involving over a dozen different dogs. Dogs with the MDR1 gene may have adverse drug reactions to over a dozen drugs, including Ivermectin (for Heartworm control), Ioperamide or Imodium (antidiarrheal), and Acepromazine (pre-anesthetic).  

Major concerns: CEA Minor concerns: distichiasis, pyotraumatic dermatitis
Occasionally seen: PDA, deafness, cerebellar abiotrophy 


Drugs that have been documented to cause problems in dogs with the MDR1 mutation include:

  • Acepromazine (tranquilizer and pre-anesthetic agent)- Based on collaborative research, the VCPL has determined that dose reductions are required for dogs MDR1 mutant/mutant and MDR1 mutant/normal

  • 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 (MDR1 mutant/mutant) and can cause toxicity in dogs that are heterozygous for the mutation (MDR1 mutant/normal).

  • Selamectin, milbemycin, 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.

  • Loperamide (ImodiumTM; antidiarrheal agent)- At doses used to treat diarrhea, this drug will cause neurological toxicity in dogs with the MDR1 mutation. This drug should be avoided in all dogs with the MDR1 mutation.

  • Butorphanol (analgesic and pre-anesthetic agent)- Dose reduction required for dogs MDR1 mutant/mutant and MDR1 mutant/normal.

  • Chemotherapy Agents (Vincristine, Vinblastine, Doxorubicin, Paclitaxel)- Based on collaborative research, the VCPL has determined that dose reductions are required for dogs MDR1 mutant/mutant and MDR1 mutant/normal in order to avoid SEVERE toxicity

  • For more information on Collie health, go to http://www.colliehealth.org.

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