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Allopurinol is a medication used to prevent gout attacks. It works by dissolving uric acid crystals slowly, over several months, by lowering uric acid in the blood. Allopurinol lowers the amount of uric acid that the body makes. After several months of low uric acid levels, the uric acid crystals dissolve, reducing the risk of gout attacks. However, while uric acid crystals are dissolving, the risk of gout attacks is increased for a few months. To prevent gout attacks in the first few months of taking allopurinol, anti-inflammatory medications such as colchicine and NSAIDs may be added until the risk decreases.
Allopurinol is usually taken in the morning with food and water. Because dehydration can worsen gout, it is important to stay hydrated while taking allopurinol. Allopurinol lowers uric acid levels within a few days; however, it may take up to 6 months before crystallized uric acid dissolves, if uric acid levels are lowered enough (to less than 6 mg/dl). Allopurinol is usually started at lower dose and increased over time to reach an acceptable uric acid level.
Some patients (Han Chinese, Thai and Korean) have a genetic predisposition to allergic reactions to the allopurinol in this medication, and your provider may check this (HLA- B5801) marker before starting.
The most significant side effect for allopurinol is the risk of an allergic reaction. If you develop any skin itching, rashes or hives, you should discontinue allopurinol immediately and inform your provider. Allopurinol is safe to use in chronic kidney disease but start doses must be low and slowly increased over time.
You should notify your doctor if you have a history of liver or kidney disease. Also, let your doctor know if you have ever had or develop a reaction to allopurinol, particularly a skin rash or allergic reaction. Make sure to notify your other physicians while you are taking this drug, especially if you are taking azathioprine or 6-mercaptopurine. If you are pregnant or considering pregnancy, let your doctor know before starting this medication. Women should discuss birth control with their primary care physicians or gynecologists. Breast-feeding should be avoided while taking allopurinol. The risk in pregnancy and breastfeeding has not been determined.
Written March 2019 by Suleman Bhana, MD, and reviewed by the American College of Rheumatology Committee on Communications and Marketing.
This patient fact sheet is provided for general education only. Individuals should consult a qualified health care provider for professional medical advice, diagnosis and treatment of a medical or health condition.