Collies and some other breeds may possess a mutation called MDRI that affects how they respond to certain medicines. Use of these drugs in a Collie that carries this mutation can cause serious neurological issues or death. MDR1 is the abbreviated name of the gene called Multi-Drug Resistance 1.
This mutation and drug sensitivity is something you need to make sure your vet is aware of when they are prescribing medications. If there is any question, ask your vet to test your dog to see if they carry this mutation prior to any medical procedures or before prescribing certain drugs.
Here is a list of drugs known to affect sensitive Collies:
- Antiparasitic agents: ivermectin, milbemycin oxime, selecamectin, moxidectin, abamectin
- Gastrointestinal agents: loperamide (over-the-counter antidiarrheal agents, e.g., imodium AD, some formulas of Kaopectate and PeptoBismol)
- Anticancer agents: oxorubicin, vincristine, vinblastine
- Immunosuppressive agents: Cyclosporin, cyclosporin A, tacrolimus
- Cardiac agents: digoxin, quinidine
- Antibiotics: erythromycin, grepafloxacin
- Steroids: dexamethasone, hydrocortisone
- Tranquilizers: acepromazine
- Pain control: butorphanol, ondansetron
Here is a list of drugs that could affect sensitive Collies*
Technical Description of MRDI:
There is a mutation at the MDR1 locus (mdr1-1?) that causes a defect in the blood-brain barrier, mediated by P-glycoprotein, an ATP-dependent drug transporter that moves a broad spectrum of substrates across several tissue borders throughout the body.
Drug sensitivity status, explained:
Collies that are homozygous for the mdr1-1? mutation are highly sensitive to the drugs listed and may suffer severe or even fatal neurotoxicoses when the drugs are administered at normal therapeutic doses (except for the monthly treatments for heartworm and fleas, which are safe). Reactions include the rapid onset of respiratory failure; respirator support may be necessary as a life saving measure.
Collies that are heterozygous at the MDR1 locus may still show sensitivity to the drugs listed, suffering neurological symptoms even at normal therapeutic doses. Therefore these drugs should be administered with caution and the dog’s reaction closely monitored. Use of the drug should be terminated immediately if neurological signs are suspected or present.
Collies that are homozygous normal are no more sensitive to these drugs than any other dog and normal therapeutic doses can be administered.
Only 20% of collies are NORMAL/NORMAL. One in three collies is MUTANT/MUTANT on average; the rate of homozygous mutants may be higher in families of related collies. Therefore, collies of unknown status must be treated as if they are sensitive to these drugs
*Drugs that are P-glycoprotein substrates can build up dangerous levels in the brains of genetically sensitive Collies
Download a PDF of the full list, and ask your vet to save it in your dog’s file.