Musculoskeletal system -Allopurinol Flashcards
1
Q
Musculoskeletal system
Allopurinol
Common indications
A
- To prevent acute attacks of gout.
- To prevent uric acid and calcium oxalate renal stones.
- To prevent hyperuricaemia and tumour lysis syndrome associated with chemotherapy.
2
Q
Musculoskeletal system
Allopurinol
Mechanisms of action
A
- Allopurinol is a xanthine oxidase inhibitor
- Xanthine oxidase metabolises xanthine (produced from purines) to uric acid.
- Inhibition of xanthine oxidase lowers plasma uric acid concentrations and reduces precipitation of uric acid in the joints or kidneys
3
Q
Musculoskeletal system
Allopurinol
Important adverse effects
A
- The most common side effect is a skin rash, which may be mild or may indicate a more serious hypersensitivity reaction such as Stevens–Johnson syndrome or toxic epidermal necrolysis
- life-threatening reaction to allopurinol that can include fever, eosinophilia, lymphadenopathy and involvement of other organs, such as the liver and skin
- Starting allopurinol can trigger or worsen an acute attack of gout
4
Q
Musculoskeletal system
Allopurinol
Important interactions
A
- The cytotoxic drug mercaptopurine and its pro-drug azathioprine require xanthine oxidase for metabolism
- When allopurinol is prescribed with these drugs, it inhibits their metabolism and increases the risk of toxicity.
- with amoxicillin increases the risk of skin rash
- with ACE inhibitors or thiazides increases the risk of hypersensitivity reactions.
5
Q
Musculoskeletal system
Allopurinol
Practical prescribing
A
- Start at a low dose (e.g. 100 mg daily) and titrate up according to serum uric acid concentrations to usual maintenance of 200–600 mg daily in 1–2 divided doses
- When starting allopurinol for gout, NSAID or colchicine treatment should also be prescribed and continued for at least a month after serum uric acid levels return to normal to avoid triggering an acute attack
- Where allopurinol is used as part of cancer treatment, it should be commenced before chemotherapy.
