Allopurinol

What is allopurinol?

Allopurinol (Lopurin®, Zyloprim®) is a drug used to prevent the recurrence of uric acid and calcium oxalate uroliths (stones) in dogs. This medication works by decreasing the production of uric acid in the body.

It is also used in the treatment of leishmaniasis in dogs and cats and to treat gout in certain birds and reptiles. When allopurinol is prescribed in the treatment of leishmaniasis or for use in birds and reptiles, it is referred to as off-label use. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully.

"This medication works by decreasing the production of uric acid in the body."

How do I give allopurinol to my pet?

Allopurinol comes in tablet form and is given orally (by mouth). For birds, it may be added to the drinking water. It may be given with or without food. If your pet vomits or seems unwell after receiving allopurinol on an empty stomach, give the next dose with a small amount of food. If vomiting continues, contact your veterinarian. Compounded liquid forms may be prepared by your veterinarian. The liquid form must be measured carefully. Your veterinarian can provide you with a syringe to measure the correct amount. 

This medication can take up to a few weeks before effects are noted and, at times, improvement may not be visibly obvious.

Ensure your pet has free access to fresh water while taking this medication unless otherwise advised by your veterinarian.

What if I miss giving a dose to my pet?

If you miss giving your pet a dose, give the next dose as soon as you remember, but if it is close to the next scheduled dose when you remember, skip the missed dose and give it at the next scheduled time. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects of allopurinol are uncommon in dogs and cats. Some animals may vomit after receiving the medication or may exhibit other signs of stomach upset such as lack of appetite or diarrhea. When used for the long-term prevention of stones in dogs, a low-purine diet should be fed. In dogs receiving higher doses of allopurinol, certain types of bladder stones (xanthine stones) may develop. Any side effects that you observe should be reported to your veterinarian.

This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Allopurinol should be used with caution in animals that have liver or kidney problems. Do not use it in red-tailed hawks and use it cautiously in other raptors. The safety of this medication has not been determined in breeding or pregnant animals. It should be used with caution in nursing dogs.

Are there any drug interactions I should be aware of?

Caution must be taken when allopurinol is used in conjunction with certain antibiotics (e.g., amoxicillin, ampicillin), immunosuppressive drugs, diuretics, and some other medications. Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

"Monitoring of the levels of uric acid in the blood and urine may be recommended..."

Monitoring of the levels of uric acid in the blood and urine may be recommended by your veterinarian. Liver and kidney function tests may also be recommended. Monitor for signs of liver dysfunction such as yellowing of the skin, severe tiredness, or skin rash. If allopurinol is being used to treat leishmaniasis, your veterinarian will monitor the clinical signs of the disease. Because bladder stones can develop with long-term use, dogs should also be monitored for urinary problems (e.g., straining to urinate, blood in the urine, pain while urinating) while taking allopurinol. Consult your veterinarian if any of these problems occur.

How do I store allopurinol?

Store allopurinol in a tightly sealed container at room temperature (20-25°C or 68-77°F). Protect it from light. If your veterinarian has compounded a liquid form, follow the storage recommendations and expiration date for the medication printed on the label.

What should I do in case of an emergency?

Call your veterinary office immediately if you suspect an overdose or an adverse reaction to the medication. If they are not available, follow their directions in contacting an emergency facility.