Multi Drug Resistance (MDR1)

During the 1980s there were reports of collies and other herding breeds dying and being ill when given a worming medication called Ivermectin. Researchers found that this was due to a defective gene that allowed certain drugs to cross the ‘blood brain barrier’ and cause neurological symptoms. This defect was eventually found to have originated during the late 19th century in the UK.

The condition is known as MDR1 and is thought to  affect approximately 60% of Rough and Smooth Collies who are also susceptible to other drugs that have now been identified. Affected dogs can live normal and healthy lives as long as they are not given these particular drugs and in the majority of cases there are alternatives. However there are unfortunately some vets who are still unaware of the importance of MDR1 in herding breeds.  The Club recommends that all dogs are DNA tested so that their status can be reported to the vet and records marked accordingly.

Symptoms of a reaction include excessive salivation, ataxia, blindness, coma and respiratory problems and immediate veterinary advice should be sought,  Please be aware that Ivermectin type drugs are used in the worming of farm animals and horses and may be excreted in the faeces so affected dogs should be prevented from eating the droppings.

DNA results describe the dog as ‘normal‘ (+/+), where  they can only pass on healthy genes to their offspring and do not exhibit drug toxicity.

‘Carrier’ (+/-) dogs have received one abnormal gene and one healthy gene from their parents and can pass on the defect and care needs to be taken with choice of mate when breeding.  Although most carriers do not exhibit toxicity, they are susceptible to some sedatives and doses may need to be reduced.

‘Affected’ (-/-) dogs receive two mutant genes and will show toxicity to listed drugs and can only pass on defective genes to their offspring.

Letters for vets, laboratories offering DNA testing (simple cheek swab) and a list of the drugs to be avoided are provided in the left hand menu.