Xanthine oxidase inhibitors

Xanthine oxidase turns hypoxanthine into xanthine and xanthine into uric acid, the last step of purine breakdown in humans. Blocking it lowers uric acid in blood and urine, so over months the body's urate stores shrink and gout attacks become rarer. The same block slows the breakdown of azathioprine and mercaptopurine, raising their levels.

• AllopurinolThe usual first urate-lowering drug: febuxostat is kept for people who do not respond to allopurinol or cannot take it.
• FebuxostatIn the CARES trial in gout patients with heart disease, sudden cardiac death was the commonest cause of the extra cardiovascular deaths on febuxostat.

• Chronic gout, to prevent attacks
• High uric acid from cancer treatment (tumor lysis)

• Gout flares in the first months of treatmentKnown for
• Severe skin reactions (SJS, TEN, DRESS)Known forSerious
• Rash
• Liver injury and raised liver enzymesSerious
• Nausea
• Diarrhea
• Joint pain
• Bone marrow suppressionSerious

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Flares are common at the start; give colchicine or an NSAID alongside for the first months.
• They raise azathioprine and mercaptopurine levels: febuxostat is contraindicated with them, allopurinol needs their dose cut.
• Stop them as soon as a rash appears, since it can be the start of SJS, TEN or DRESS.
• Not recommended for high uric acid that causes no symptoms.

Written for biofideX in plain words, after checking these references:

• Xanthine Oxidase Inhibitor (NCI Thesaurus)
• Allopurinol tablets: label (DailyMed)
• Febuxostat tablets: label (DailyMed)
• Gout (NHS)

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.