The primary use of allopurinol is to treat hyperuricemia (excess uric acid in blood plasma) and its complications. Allopurinol does not alleviate acute attacks of gout (and can actually make them worse initially), but is useful in chronic gout to prevent future attacks.

Allopurinol is also commonly used in chemotherapeutic treatments to both reduce side effects (as these regimes can rapidly produce severe hyperuricemia) and to increase their effectiveness (Allopurinol inhibits the breakdown of mercaptopurine, therefore increasing its effect(ref Rang, Dale and Ritter Pharmacology).

Other established indications for allopurinol therapy include ischemic reperfusion injury, kidney stones with a uric acid component (uric acid nephrolithiasis), and protozoal infections (Leishmaniasis).

Because allopurinol is not a uricosuric, it can be used in patients with poor kidney function. However, allopurinol has two important disadvantages: Its dosing is complex,^[2] and some patients will be hypersensitive to it. Therefore, use of this drug requires careful monitoring.

Allopurinol can be used in patients with poor kidney function, but it may also help them. A study of allopurinol use in patients with chronic kidney disease suggested that "Allopurinol decreases C-reactive protein and slows down the progression of renal disease in patients with chronic kidney disease. In addition, allopurinol reduces cardiovascular and hospitalization risk in these subjects."^[3]

A recent study has suggested that allopurinol can help reduce the effects of angina in ischaemic heart disease by reducing the workload on the heart.^[4]

Allopurinol is used as an add-on drug for refractory epilepsy, because it is an adenosine agonist, which inhibits glutamine release from excitatory neurons, but doesn't change the plasma concentration of other epilepsy drugs.^[5]