What is allopurinol and why is it prescribed?
Allopurinol is used for the long-term treatment and prevention of gout. Taken regularly, it can stop attacks of gout and help prevent damage to the joints.
The body naturally produces a substance called urate, which is normally dissolved in the blood until it's passed out of the body in the urine. When too much urate is produced, or if the body cannot get rid of it properly, the blood can't dissolve all the urate and solid crystals can form in and around joints causing inflammation and pain.
Allopurinol blocks an enzyme called xanthine oxidase which is involved in producing urate. Over a few weeks allopurinol can lower urate levels in the blood and stop new crystals forming. Once urate levels are low enough existing crystals begin to dissolve. This can take some months and you may have more attacks of gout during this time. This is more likely if your urate levels are very high or you've had gout for a long time. It doesn't mean the drug isn't working. Attacks of gout usually stop within a year as long as your urate level has lowered sufficiently.
Usually, you'll be offered allopurinol for gout if blood tests show that your urate level is high and one or more of the following applies:
- you're having repeated attacks of gout
- your joints or kidneys have been damaged by attacks of gout
- you have deposits of urate crystals affecting your skin (gouty tophi).
Your doctor may be cautious about prescribing allopurinol if your kidney or liver function is significantly impaired.