Generally, drugs will have the same effect on any dog regardless of their breed. However, there are some exceptions that you may encounter as an owner. This article will cover the association between some breeds and certain types of drugs and how it can affect them. While your vet will be familiar with the impact on prescribed drugs, it can be very helpful for you as the owner to be clued up too!

Collies (MDR1 gene mutation)

This breed, and others such as Shetland Sheepdogs, Australian Shepherds and German Shepherds can be carriers of a gene mutation called MDR1. A ‘Mutation’ means a change to genetic code. What it does, depends on what that particular gene does – in other words, what protein that gene tells the body to make. If the gene is changed, the protein will be changed too – maybe only a little bit, but maybe enough to have a big effect. 

The MDR1 gene codes for a protein that filters drugs from the brain into the bloodstream, across something called the ‘blood-brain-barrier’. When this gene is mutated, the protein made is not functional, and allows higher levels of some drugs to build up in the brain, therefore resulting in neurological symptoms – typically, some form of seizure.

Side-effects of some drugs 

Overall, this means that these dogs are far more sensitive to the negative and side-effects of some drugs compared to the majority of the canine population. The following drugs are known to have adverse effects in affected dogs:

  • Butorphanol (used for sedation and pain relief) 
  • Acepromazine (used for sedation) 
  • Ivermectin 
  • Milbemycin 
  • Selamectin      (anti-parasitic treatments)
  • Moxidectin 
  • Doramectin
  • Vincristine 
  • Doxorubicin              (chemotherapy drugs)
  • Cyclosporine A

Sensitivity to parasite treatments is most commonly talked about with these breeds. But it is important to be aware that these dogs will also likely be affected differently by anaesthetic drugs. Usually how sedated they become and how long this sedation lasts for. However, many of these drugs (such as milbemycin, selamectin, or moxidectin) can still be used safely at controlled doses. For those which cannot, alternatives can be chosen.

Some chemotherapy drugs may have gastro-intestinal side effects, even at low doses on these breeds.

This gene is passed on from parent to offspring, and can be affected whether they receive it from both parents or just one. However, an animal is likely to be worse affected when both parents have this mutation. A DNA test can be performed through the Kennel Club. This is very important to do if you are considering breeding from your dog. 

With these breeds it is very important you talk with your vet about parasite control, including drugs that will be suitable to use together for your pet. 

Sighthounds (CYP2B11 gene mutation)

Breeds such as greyhounds, whippets and Rhodesian Ridgebacks may be affected by this gene mutation. It alters the ability of their liver to produce an enzyme called ‘cytochrome P450’, which helps to metabolise drugs, particularly commonly used anaesthetic drugs. Therefore, these breeds will metabolize the drugs more slowly and it is likely that they will take longer to recover from an anaesthetic, as it will take more time for the drugs to be removed from their body. Generally, this means that they will need a little more monitoring during the recovery period.


This breed are more sensitive to a group of antibacterial drugs called sulphonamides, likely due to a gene mutation. These drugs can be used to treat urinary tract, skin and gastrointestinal infections. There is evidence that these drugs can negatively affect Dobermanns, causing side effects such as fever, liver toxicity and dry eye. Therefore, sulphonamide use is often avoided or at least minimised in this breed. 


There is some anecdotal evidence that Boxers are more sensitive to an anaesthetic drug called Acepromazine. While there is no published evidence, lots of vets will still use this drug only at a much lower dose.

In conclusion…

It is natural to be concerned about the side effects of any drugs prescribed for your animal – if you have any concerns about how a drug may affect your pet, speak with your vet. Remember, if you think your dog may have had a reaction, seek help right away.

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