A 54-year-old man comes to the emergency room complaining of severe pain in his right toe. The pain is interfering with his ability to walk and he reports no prior trauma to the toe. He has had multiple less severe episodes in the past, which he always treats with pain medications.On physical examination, the toe is red, inflamed, and exquisitely sensitive to movement. An x-ray of the toe is normal and needle aspiration of the joint confirms uric acid crystals. He is treated with oral indomethacin (NSAID) for 7 days, and 1 month later he remains symptom free. Allopurinol is recommended for prevention of this condition. Which of the following is the most likely mechanism of action of allopurinol?
A 54-year-old man comes to the emergency room complaining of severe pain in his right toe. The pain is interfering with his ability to walk and he reports no prior trauma to the toe. He has had multiple less severe episodes in the past, which he always treats with pain medications.On physical examination, the toe is red, inflamed, and exquisitely sensitive to movement. An x-ray of the toe is normal and needle aspiration of the joint confirms uric acid crystals. He is treated with oral indomethacin (NSAID) for 7 days, and 1 month later he remains symptom free. Allopurinol is recommended for prevention of this condition. Which of the following is the most likely mechanism of action of allopurinol?
💡 Explanation
**Question:** A 54-year-old man comes to the emergency room complaining of severe pain in his right toe. The pain is interfering with his ability to walk and he reports no prior trauma to the toe. He has had multiple less severe episodes in the past, which he always treats with pain medications. On physical examination, the toe is red, inflamed, and exquisitely sensitive to movement. An x-ray of the toe is normal and needle aspiration of the joint confirms uric acid crystals. He is treated with oral indomethacin (NSAID) for 7 days, and 1 month later he remains symptom free. Allopurinol is recommended for prevention of this condition. Which of the following is the most likely mechanism of action of allopurinol?
A. Inhibits the production of uric acid
B. Increases the excretion of uric acid
C. Reduces the solubility of uric acid crystals
D. Increases the absorption of uric acid
**Correct Answer:**
**Core Concept:** Gout is a form of inflammatory arthritis caused by the deposition of monosodium urate crystals in joints, leading to acute attacks and chronic joint damage. The primary pharmacological target of uric acid lowering therapies, such as allopurinol, is to decrease the production of uric acid.
**Why the Correct Answer is A:**
Allopurinol, a xanthine oxidase inhibitor, works by inhibiting the enzyme xanthine oxidase. This enzyme is responsible for the production of uric acid in the body.
When allopurinol is administered, it prevents the production of uric acid, resulting in lower serum uric acid levels. As a result, the accumulation of uric acid crystals in joints is reduced, preventing gout attacks and chronic joint damage.
**Why Other Options are Incorrect:**
**Option B:** Allopurinol does not increase the excretion of uric acid. Instead, it lowers the serum uric acid levels, as explained above.
**Option C:** Allopurinol does not directly affect the solubility of uric acid crystals. Its primary mechanism is to lower the uric acid levels in the blood, which indirectly reduces the formation of uric acid crystals.
**Option D:** Allopurinol does not increase uric acid absorption. Its function is to decrease uric acid production, thereby preventing the precipitation of uric acid crystals in joints and preventing gout attacks and chronic joint damage.
✓ Correct Answer: A. inhibition of xanthine oxidase
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