<prompt> A 74-year-old man with a previous episode of gout is given allopurinol. Which of the following is the most likely mechanism of action for this medication?increasing uric acid productionblocking excretion of uric acid by renal tubular mechanisminhibiting xanthine oxidasediminishing inflammation of acute gouty arthritis  <response>: Allopurinol effectively blocks uric acid production by inhibiting xanthine oxidase. Allopurinol is indicated in patients with a history of uric acid calculi of the urinary tract. In addition, it is often used in patients with malignancy e.g., leukemia, lymphoma, particularly when chemotherapy or radiation therapy is being used. 