Allopurinol Side Effects in Dogs

If you've decided to give your pet a treatment regimen of allopurinol or a related medicine, you'll likely be wondering what the potential allopurinol side effects are for your dog. Allopurinol can be a very helpful drug, particular for certain types of dogs. Breeds like Dalmatians are at a high risk for developing urate bladder stones. These stones can not only be painful, but they can also cause serious harm and damage to your pet's urinary tract and bladder system. Allopurinol is used to help break up and alleviate these stones, as well as to prevent them from occurring in the first place.

Negative Drug Reactions

Like most medicines, allopurinol can react negatively with certain other medicines in your pet's system. The exact causes for this are based on the chemicals and the interactive chemistry of the drugs. It's difficult to predict what the exact effect will be on your dog, but it's generally best to avoid giving him allopurinol if any of the following drugs are in his system already:

  • methionine
  • ammonium chloride
  • azathioprine
  • furosemide

Likewise, it's not a good idea to give your pet any of these other medicines while he's already subscribed to allopurinol as well.

Gastrointestinal Upset

Although it's very uncommon in dogs, some animals have been reported to show signs of gastrointestinal upset as a result of taking allopurinol. The various symptoms of gastrointestinal upset differ depending upon the animal in question, but they generally include vomiting or diarrhea, as well as a general loss of appetite. If this upset continues for a long time your pet may suffer malnutrition as a result of not eating enough. This can, in turn, lead to malaise, lethargy and irritable behavior, among other dangerous and less severe side effects as well.

Liver Damage

Dogs with any preexisting liver or kidney conditions should not take allopurinol. The reason for this is that this medicine has been known in rare occasions to cause some types of liver and kidney cell damage. While this is not a major concern for most animals, it's still a good idea to have your vet check in on your pet's liver and kidney hormone levels regularly, particularly if he'll be on the allopurinol treatment for any extended period of time.

Kidney Stones

Ironically enough, allopurinol can, in very rare cases, cause kidney stones. While eliminating urate bladder stones, the drug has been known to cause a type of stone called a xanthine stone as well. This typically is only a concern for dogs that have been taking allopurinol for a long period of time, but it's an important side effect to be aware of nonetheless. These stones, when they do develop, are quite serious and painful for your pet.

For more information about allopurinol and for a prescription for this medicine, you'll need to take your pet in to a veterinarian in order to have him properly examined and diagnosed first. Allopurinol is available by the brand name Zyloprim.