Multidrug Resistance MDR1 gene expresses a protein involved in the transport of biological substances through the blood-brain barrier of dogs. Recently, a mutation (nt230[del4]) in the MDR1 gene has been shown to be predisposed in some breeds that can result in adverse reactions to some commonly administered drugs such as ivermectin and ioperamide. In affected dogs, exposure of these drugs at the normal administered dose can result in serious neurological side effects such as hypersalivation, ataxia, blindness, tremor, respiratory distress and even death.
Affected breeds:
Collie (approx. 50-75% are affected by the MDR1 gene mutation), Australian Shepherd, Shetland Sheepdog, Old English Sheepdog, Border collie, English Shepherd, German Shepherd, White Shepherd, Waller, Silken Windhound, McNab and a variety of mixed breed dogs
Implicated drugs:
Anti-Parasitic Drugs - Ivermectin substances: Diapec®, Ecomectin, Equimax, Eqvalan, Ivomec, Noromectin, Paramectin, Qualimec, Sumex & Virbamec
Doramectine substances:Dectomax, Moxidectine substances: Cydectin & Equest
Loperamide substances - Immodium [anti-diarrhoeal]
Metronidazole substances - Flagyl
Chemotherapy Agents - Vinblastine, Doxorubicine, Paclitaxel, Docetaxel, Methotrexat & Vincristine Glucocorticoids (Steroids commonly used to treat auto-immune diseases): Dexamethason
Immuno-suppressives: Cyclosporine A
Heart glycosides: Digoxine & Methyldigoxine
Antiarrhythmics: Verapamil, Diltiazem & Chinidine
Analgesics - Morphine & Butorphenol
Anti-emetics: Metoclopramide, Ondansetron & Domperidon
Antibiotics - Sparfloxacin, Grepafloxacin; Erythromycin
Antihistamines - Ebastin
Tranquillisers - Acepromazine
Other drugs; Etoposide; Mitoxantrone; Ondansetron; Paclitaxel; Rifampicin.
- Note: It is recommended that dosages are reduced by 25% in MDR1 carriers (normal / mutant) and by 30 -50% in MDR1 affected dogs (mutant / mutant).
Interpretation of the results:
Results will indicate whether the dog is;
- Normal - Both copies of the gene are normal hence the dog will not display the disease symptoms, nor will it pass the mutant copy to its offspring (N / N).
- Carrier - One copy of the gene is normal and one copy is a mutant copy. These dogs may display the disease symptoms and also may pass the mutant copy to its offspring (N / mut).
- Affected - Both copies of the gene are mutant and these dogs are very likely to display the disease symptoms. Affected dogs will pass the mutant copy to its offspring (mut / mut).
