Zyloprim (allopurinol) Side Effects, Warnings, and Drug Interactions

Zyloprim (allopurinol) is a xanthine oxidase inhibitor used to prevent and/or treat acute attacks of gout, erosive destructive gouty joint disease, uric acid deposits in tissues (tophi), gouty kidney disease, and uric acid stones. 

Zyloprim also is used to prevent elevation of blood uric acid in patients undergoing chemotherapy for the treatment of certain cancers and in patients with recurrent calcium kidney stones and elevated uric acid levels.

Hyperuricemia occurs when the body produces more uric acid than it can eliminate. The uric acid forms crystals in joints (gouty arthritis) and tissues, causing inflammation and pain. Elevated blood uric acid levels also can cause kidney disease and kidney stones. 

Common side effects of Zyloprim include:

• diarrhea,
• nausea,
• rash,
• itching,
• and drowsiness.

Serious side effects of Zyloprim include:

• numbness or tingling of arms or legs,
• easy bleeding or bruising,
• signs of infection (e.g., fever, persistent sore throat),
• unusual tiredness,
• bloody or painful urination,
• change in the amount of urine,
• yellowing eyes or skin (jaundice),
• severe stomach/abdominal pain,
• persistent nausea or vomiting,
• dark urine,
• unusual weight loss,
• eye pain,
• and vision changes.

Zyloprim interacts with oral mercaptopurine, azathioprine, and warfarin by reducing their breakdown in the body which increases the blood levels of these drugs. Zyloprim, when taken with penicillin antibiotics, increases risk of skin rash. 

There are no adequate studies of Zyloprim in pregnant women. Zyloprim is excreted in breast milk. To avoid adverse effects in the infant, nursing mothers taking Zyloprim should consider not breastfeeding.

Common side effects include:

• diarrhea,
• nausea,
• rash,
• itching, and
• drowsiness.

Common side effects of Zyloprim include:

• diarrhea,
• nausea,
• rash,
• itching,
• and drowsiness.

Serious side effects of Zyloprim include:

• numbness or tingling of arms or legs,
• easy bleeding or bruising,
• signs of infection (e.g., fever, persistent sore throat),
• unusual tiredness,
• bloody or painful urination,
• change in the amount of urine,
• yellowing eyes or skin (jaundice),
• severe stomach/abdominal pain,
• persistent nausea or vomiting,
• dark urine,
• unusual weight loss,
• eye pain,
• and vision changes.

There are no adequate studies of allopurinol in pregnant women.

Allopurinol is excreted in breast milk. To avoid adverse effects in the infant, nursing mothers taking allopurinol should consider not breastfeeding.

Allopurinol increases blood levels of oral mercaptopurine (Purinethol) and azathioprine (Imuran) by reducing their breakdown in the body. Therefore, the dose of mercaptopurine and azathioprine should be reduced in order to avoid toxicity. There is an increased risk of skin rash in patients taking allopurinol in combination with penicillins. Allopurinol may increase the effect of warfarin by reducing its breakdown.