Allopurinol for Dogs

Allopurinol is used for dogs in helping in the prevention of the formation of bladder stones by inhibiting uric acid production. However, the FDA has not approved the use of the medication yet. Since a dog will more than likely be on this medication for his lifetime, urine excretion tests are needed at least once yearly in order to measure the effectiveness of the medication. Specialty foods may be used in conjunction with allopurinol in order to control the formation of bladder stones.

Bladder Stones in Dogs

Since normal urine is bacteria-free, the only way for bacteria to enter the bladder is through the urethra. These bacteria can cause pain, inflammation, urine stones or crystals within the bladder, causing the pH balances in the body to change. Usually small stones are capable of being passed in the urine through the urethra. Inflammation can cause the urethra to narrow, thus preventing even small stones to pass but instead remain inside the bladder.

Large bladder stones are a bigger risk since they can block the elimination of urine causing more serious health problems since urine is toxic. Allopurinol reduces the uric acid in the bloodstream, preventing the formation of uric acid crystals.

Ultrasound and/or x-rays can confirm the presence of bladder stones. Using a combination of a special diet and allopurinol, bladder stones can be treated. However, for worse case scenarios, surgery or sonic vibrations that break up the bladder stones may be used so that the stones can pass through the urethra.

Here is a list of signs that indicate an urinary infection, which can, but not necessarily will, lead to bladder stones:

  • Difficulty urinating or straining to urinate
  • Urinating in unacceptable places
  • Pain when urinating
  • Lack of urine control (incontinence)
  • Frequent urination
  • Urine leakage
  • Blood in the urine
  • Licking private area
  • Urine odor
  • Increased thirst
  • Lethargy
  • Skin issues in the vaginal area
  • Behavioral problems

Side Effects of Allopurinol

Side effects when using allopurinol are uncommon, but can include:

  • Diarrhea
  • Vomiting
  • Upset stomach
  • Blood in the urine
  • Cramping
  • Nausea
  • Liver damage
  • Skin rash
  • Anemia, as a result of bone marrow suppression
  • Allergic reactions (rare), such as hives or facial swelling

Allopurinol should not be used:

  • In dogs with kidney disease
  • In dogs with liver disease
  • Pregnant dogs
  • In lactating dogs
  • In puppies
  • In conjunction with probenecid due to a possible increase in the effectiveness of allopurinol
  • In conjunction with loop diuretics (furosemide) due to a possible decrease in the effectiveness of allopurinol because the use of diuretics may increase levels of uric acid
  • In conjunction with cyclophosphamide, which may cause an increased risk in bone marrow suppression (side effect of chemotherapy)
  • In conjunction with amoxillin or ampicillin due to an increased risk of skin rashes
  • In conjunction with anticoagulants (warfarin) due to an increased risk of bleeding

The use of any other medication with allopurinol should be authorized by a veterinarian since some medications do not mix well with allopurinol. Allopurinol must be stored in a tightly closed container, at room temperature, away from any light, moisture or excessive heat.