Overview
Allopurinol is a widely used urate-lowering medication primarily indicated for the long-term management of gout and the prevention of uric acid kidney stones. It is highly effective in reducing elevated blood uric acid levels (hyperuricemia) to prevent recurrent gout attacks.

Mechanism of Action
It functions as a xanthine oxidase inhibitor. Xanthine oxidase is the enzyme responsible for the conversion of hypoxanthine to xanthine, and subsequently xanthine to uric acid. By inhibiting this enzyme, allopurinol significantly decreases the production of uric acid in the body.

Dosage and Administration
Therapy is typically initiated at a low dose (e.g., 100 mg daily) to minimize the risk of triggering an acute gout flare. The dose is gradually titrated upwards, guided by serum uric acid levels, often reaching a maintenance dose of 300 mg daily. It should be taken after meals.

Side Effects
The most common side effect is a maculopapular skin rash. Rarely, it can cause severe, potentially fatal hypersensitivity reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis. Other potential adverse effects include gastrointestinal distress and hepatic enzyme elevation.

Contraindications
It is contraindicated in patients with a known severe hypersensitivity to allopurinol. It should not be started during an acute gout attack, as it may exacerbate or prolong the flare. Caution and dose adjustment are required in patients with renal impairment.

Pregnancy and Lactation
There is limited data regarding its safety during pregnancy; therefore, it should be used only if clearly needed and the potential benefit justifies the risk. Allopurinol and its active metabolite are excreted in human breast milk, so caution is advised during lactation.