<prompt> A 74-year-old man reports having multiple gouty attacks of his left big toe. He is symptom free currently and is prescribed allopurinol for gout prophylaxis. 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 eg, leukemia, lymphoma, particularly when chemotherapy or radiation therapy is being used. 