Drug class · Joints & ligaments
Xanthine oxidase inhibitors
Also known as: urate-lowering therapy
Medicines that lower uric acid by blocking the enzyme that makes it, dissolving the crystals that cause gout attacks and tophi when taken every day.
- Biological target
- Xanthine oxidase
- Also called
- urate-lowering therapy
Mechanism of action
Xanthine oxidase converts hypoxanthine and xanthine into uric acid at the end of purine breakdown. Blocking it drops blood urate below its saturation point, so no new crystals form and existing deposits slowly dissolve. Attacks can increase for the first months as crystals mobilise, so an NSAID or colchicine is given as cover, and the dose is raised until the urate target is reached.
Members of the class
allopurinolfebuxostat
Members with a page on this site are linked.
Conditions treated
Class effects
- Rash, nausea
- Gout flares in the first months
Cautions
- Allopurinol hypersensitivity syndrome, rare but severe; HLA-B*58:01 screening in higher-risk populations
- Interaction with azathioprine and mercaptopurine
- Febuxostat: cardiovascular caution
Class warnings
- Allopurinol can cause severe hypersensitivity (rash, fever, organ involvement), more often with kidney impairment, high starting doses and the HLA-B*58:01 allele common in some East Asian populations; any rash is a reason to stop. Starting treatment can provoke gout flares, so cover with an anti-inflammatory is given. UK
Class interactions
| With | Effect | Source |
|---|---|---|
| Azathioprine and mercaptopurine | Xanthine oxidase inhibition greatly increases their levels and toxicity (bone-marrow suppression); doses are cut to a quarter or the combination avoided. | UK |
| Amoxicillin and ampicillin | Increased incidence of rash. | UK |
| ACE inhibitors and thiazides | Increased risk of hypersensitivity reactions, particularly with kidney impairment. | UK |
Open the Drug Interaction Checker
Educational content. A drug class page describes what a family of medicines has in common. Individual medicines differ in dose, licensing and interactions; treatment choices belong to a prescriber.