Why does taking allopurinol trigger gout?

Allopurinol is the most commonly used uric acid-lowering drug in clinical practice and is the first-line agent for reducing uric acid levels. Allopurinol is an inhibitor of xanthine oxidase. By inhibiting the activity of this enzyme, it reduces the production of uric acid during purine metabolism, thereby lowering serum uric acid levels. Clinically, it is not uncommon for some patients to experience gout flares or worsening of gout symptoms after starting allopurinol. This occurs because the rapid reduction in serum uric acid levels following allopurinol administration leads to significant fluctuations in the body's uric acid concentration, which may trigger acute gout attacks or exacerbate existing gout.