What is allopurinol?Allopurinol (brand names 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 is usually combined with other drugs.
When allopurinol is prescribed in the treatment of leishmaniasis, it is referred to as ‘extra-label’ or ‘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. How do I give my pet allopurinol?Allopurinol comes in tablet form and is given orally (by mouth). It may be given with or without food. If your pet vomits or acts sick after receiving the drug on an empty stomach try giving 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 help 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.
What if I miss giving my pet the medication?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. 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. 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 by your veterinarian. Liver and kidney function tests may also be recommended.
If allopurinol is being used to treat leishmaniasis, your veterinarian will be monitoring the clinical signs of the disease.
Because there is the possibility for bladder stones to develop with long-term use, dogs should also be monitored for urinary signs (straining to urinate, blood in the urine, pain) while taking allopurinol and taken to your veterinarian if any of these signs occur.
How do I store allopurinol?Store allopurinol in a tightly sealed container at room temperature. If your veterinarian has compounded a liquid form, follow the storage recommendations and expiration date for the product printed on the label.
What should I do in case of emergency?If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

This client information sheet is based on material written by Rania Gollakner, BS DVM© Copyright 2018 LifeLearn Inc. Used and/or modified with permission under license.