Musculoskeletal system Flashcards
What are the three indications of allopurinol?
- 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.
What is allopurinol? How does it work?
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.
What are the important adverse effects of allopurinol?
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.
Drug hypersensitivity syndrome is rare.
Starting allopurinol can trigger or worsen an acute attack of gout.
When should the dose of allopurinol be reduced?
Allopurinol is metabolised in the liver and excreted by the kidney. The dose should therefore be reduced in patients with severe renal or hepatic impairment.
What are the important drug interactions with allopurinol? (3)
- 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.
- Co-prescription of allopurinol with amoxicillin increases the risk of skin rash.
- Allopurinol and ACEi or thiazides increases the risk of hypersensitivity reactions.
Why does allopurinol increase the risk of mercaptopurine/azathioprine toxicity?
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.
When starting allopurinol for gout, what other treatment should be prescribed and for how long, to avoid triggering an acute gout attack?
When starting allopurinol for gout, NSAID or colchicine treatment should also be prescribed and continued for at least one month after serum uric acid levels return to normal to avoid triggering an attack.
Where allopurinol is used as part of cancer treatment, when should it be commenced?
Before chemotherapy.
When should allopurinol be taken?
Allopurinol should be taken after meals and patients should be encouraged to maintain good hydration with fluid intake of 2-3 litres daily.
What should be done to allopurinol treatment if a rash develops?
Stopped, recommenced cautiously once the rash resolves.
What are the two aminosalicylates commonly prescribed?
Mesalazine: first line in treatment of mild-moderate ulcerative colitis.
Sulfasalazine: one of the several options for management of rheumatoid arthritis, in which it is used as a disease-modifying antirheumatic drug (DMARD), usually as part of combination therapy.
What is the common indiaction for mesalazine?
First line treatment in mild-moderate ulcerative colitis.
What is the indication for sulfasalazine?
One of the several options for the management of RA, usually as part of combination therapy.
How do aminosalicylates such as mesalazine and sulfasalazine work in Ulcerative colitis?
They work by releasing 5-aminosalicylic acid (5-ASA), which has both anti-inflammatory and immunosuppressive effects and appears to act topically on the gut rather than systemically.
For this reason, 5-ASA preparations are designed to delay delivery of the active ingredient to the colon.
What does sulfasalazine consist of?
Sulfasalazine consists of a molecule of 5-ASA linked to sulfapyridine.
In the colon, bacterial enzymes break this link and release the two molecules.
Sulfapyridine has no beneficial effect in UC but does cause Side effects. However, it does have a probably beneficial role in RA.
