Multidrug Sensitivity (MDR1) Genetic Test | GenSol Diagnostics
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Multidrug Sensitivity (MDR1)


The MDR1 gene, or multi-drug resistance gene, codes for a protein that is responsible for protecting the brain by transporting potentially harmful chemicals away from the brain. In certain breeds, a mutation occurs in the MDR1 gene that causes sensitivity to Ivermectin, Loperamide, and a number of other drugs. Dogs with this mutation have a defect in the P-glycoprotein that is normally responsible for transporting certain drugs out of the brain. The defective protein inhibits the dog’s ability to remove certain drugs from the brain, leading to a buildup of these toxins. As a result of accumulation of toxins, the dog can show neurological symptoms, such as seizures, ataxia, or even death. Dogs that are homozygous for the MDR1 gene, meaning that they have two copies of the mutation, will display a sensitivity to Ivermectin, and other similiar drugs. Dogs that are heterozygous, meaning they have only one copy of the mutation, can still react to these drugs at higher doses.

The following is a partial list of drugs known to have a negative effect on dogs with the MDR1 mutation:

Acepromzazine, Aldosterone, Amitriptyline, Antiemetics, Apomorphine, Buprenorphine, Butorphanol, Chinidin, Cimeditine, Cortisol, Cysolporin A, Dexamethasone, Digoxin, Diltiazem, Domperidone, Doxorubicin, Doxycycline, Ebastine, Erythromycin, Estradiol, Etoposide, Fentanyl, Fexofenadine, Grepafloxacin, Hydrocortisone, Ivermectin, Itraconazole, Ketoconazole, Loperamide, Losartan, Methylprednisolone, Metoclopramide, Metronidazole, Milbemycin, Mitoxantrone, Morhpine, Moxidectin, Ondansetron, Paclitaxel, Phenothiazines, Phenytoin, Quinidine, Ranitidine, Rifampin, Rifamycin,  Selamectin, Sparfloxacin, Tacrolimus, Tetracycline, Verapamil, Vinblastine, Vincristine

Additional drugs beyond this list could have a negative effect on dogs with the MDR1 mutation and it is recommended to consult a licensed veterinarian for more information.

Australian Shepherd
Border Collie
English Shepherd
German Shepherd
Long-haired Whippet
Old English Sheepdog
Shetland Sheepdog
Silken Windhound

A (CLEAR/NORMAL): These dogs have two copies of the normal gene and will neither develop MDR1 nor pass this mutation to their offspring.

B (CARRIER/AFFECTED): These dogs have one copy of the normal gene and one copy of the mutation associated with this disease. They can react to certain drugs at higher doses and pass the mutation to 50% of its offspring, on average.

C (AT RISK/AFFECTED): These dogs have two copies of the mutation associated with this disease and which results in sensitivity to a number of drugs including but not limited to Ivermectin, Loperamide, Doxorubicin, Cyclosporin, Digoxin, Acepromazine, Butorphanol and others.

Multidrug Sensitivity (MDR1)

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