**Question:** Red man syndrome is due to -

A. Indomethacin
B. Nitrates
C. Aspirin
D. Amoxycillin

**Correct Answer:** D. Amoxycillin

**Core Concept:** Red man syndrome is a rare adverse reaction to certain medications, characterized by a reddish-red rash primarily involving the face, neck, and upper trunk, which occurs after several days of therapy. This reaction is due to the accumulation of a biologically inactive product of the drug's breakdown, called "penicillamine-induced methemoglobinemia."

**Why the Correct Answer is Right:** Amoxycillin is a penicillin antibiotic that is converted into penicillamine in the liver. This penicillamine, when accumulated, can cause methemoglobinemia, leading to the characteristic features of Red man syndrome. The other options are unrelated to this reaction:

A. Indomethacin (nonsteroidal anti-inflammatory drug) and B. Nitrates (used for angina and hypertension) are not involved in the formation of methemoglobinemia.

**Why Each Wrong Option is Incorrect:**

B. Nitrates (e.g., Isosorbide) are commonly used in the management of angina pectoris and hypertension. They work by increasing the supply of oxygenated blood to the heart and lowering blood pressure. Nitrates do not cause Red man syndrome as they do not produce methemoglobinemia.

C. Aspirin (salicylic acid) is an anti-inflammatory drug, commonly used as an analgesic, antipyretic, and anti-inflammatory agent. It does not cause Red man syndrome as it does not lead to the accumulation of penicillamine, which is responsible for the reaction.

A. Indomethacin is a nonsteroidal anti-inflammatory drug (NSAID) that inhibits the enzyme cyclooxygenase (COX), responsible for the synthesis of prostaglandins, thromboxanes, and leukotrienes. Indomethacin does not cause Red man syndrome since it does not lead to the formation of methemoglobinemia.

D. Amoxycillin (a penicillin antibiotic) is responsible for the correct answer, as it leads to the accumulation of penicillamine, which causes methemoglobinemia resulting in Red man syndrome.

**Clinical Pearl:** Understanding the pathophysiology of Red man syndrome helps in recognizing the adverse reactions to amoxicillin and other penicillin antibiotics. Promptly stopping the offending medication and providing supportive care can prevent complications and alleviate the patient's symptoms.