Competitive inhibitors are used in clinical and biological situations. They are frequently called antagonists or antimetabolites of the substrates with which they compete.

1. Treatment of Gout
   1. Xanthine oxidase is an enzyme of purine catabolism, which catalyses the oxidation of hypoxanthine to xanthine and xanthine to uric acid. 
   2. Xanthine oxidase is a dimeric proteins of identical 130kD subunits, each of which contains a few election transfer agents – an FAD, an Mo complex that cycles between its Mo(VI) and Mo(IV) oxidation state and two different Fe-S clusters.
   3. Allopurinol, an analog of hypoxanthine, in which the position of N₇ and C₈ are interchanged competitively, inhibits xanthine oxidase.