MDR1
Easy-to-Understand Explanation: MDR1 is a genetic mutation that affects some dogs’ ability to handle certain medications, like Ivermectin (often used in heartworm prevention). Dogs with MDR1 cannot clear these drugs from their system properly, leading to toxic build-up in their cells. Around 50% of Australian Shepherds are affected by MDR1. Even dogs that are clear of the mutation can sometimes react to these drugs, although they typically have a lower risk. For this reason, when we medicate all our Aussies we treat them as if they are MDR1 positive regardless if they are or are not.
More Detailed Explanation: MDR1 is a genetic mutation in the ABCB1 gene, which produces a protein called P-glycoprotein (P-GP). This protein acts like a pump, helping control the movement of drugs in and out of cells, particularly in the brain. In dogs with MDR1, this pump doesn’t work as it should, causing medications to build up to toxic levels in the cells. You can think of it like a sink with a partially blocked drain—when water flows in, it backs up instead of draining away. Similarly, medications can accumulate in the cells of MDR1-affected dogs, leading to potential harm.
Below are some but not all medications that can cause issues if a dog is MDR1 positive! Thankfully you can have MDR1 noted in your pet’s records at the vet if your pet is a carrier and the vet will avoid giving them anything known to cause an issue.
Acepromazine – Prescription tranquilizer (sedative)
Butorphanol – Opioid analgesic used for pain control
Cyclosporine – Immunosuppressive agent (used for conditions like autoimmune diseases and organ transplants)
Digoxin – Cardiac glycoside used to treat congestive heart failure
Doxorubicin – Chemotherapy drug used in cancer treatment
Doramectin – Anti-parasitic medication (often used in livestock)
Emodepside – Anti-parasitic medication (primarily for heartworm treatment)
Erythromycin – Antibiotic used to treat bacterial infections like diarrhea, skin infections, and prostate infections
Ivermectin – Anti-parasitic medication commonly found in wormers and flea preventatives
Loperamide – Anti-diarrheal medication (e.g., Imodium)
Milbemycin – Anti-parasitic used for heartworm prevention and treatment of other parasites
Moxidectin – Anti-parasitic medication used in heartworm prevention
Paclitaxel – Chemotherapy drug used in cancer treatment
Rifampin – Antibiotic used for treating various bacterial infections
Selamectin – Anti-parasitic medication (found in treatments like Revolution)
Vinblastine – Chemotherapy drug used in cancer treatment
Vincristine – Chemotherapy drug used in cancer treatment
Albendazole – Anti-parasitic used to treat roundworms, tapeworms, and giardia
Amitraz – Insecticide and acaricide used in treatments for ticks and mites
Clindamycin – Antibiotic used for treating bone and soft tissue infections
Lufenuron – Flea treatment (inhibits flea egg development)
Praziquantel – Used to treat tapeworm infestations
Spinosad – Flea control medication
Tolfenamic Acid – Non-steroidal anti-inflammatory (NSAID) for pain and inflammation
Zonisamide – Anticonvulsant medication used to treat seizures
Ketonazole – Antifungal medication