Question

Which of the following statements is CORRECT regarding the pharmacology of N-acetylcysteine (NAC)?

• A. It acts as a precursor for glutathione synthesis
• B. It is used as antidote for organophosphate poisoning
• C. It inhibits cyclooxygenase enzyme
• D. It is a specific antidote for benzodiazepine overdose

Hint:

NAC is the antidote for paracetamol toxicity and works by replenishing an important intracellular antioxidant.

Answer 1

The Correct Option is A

Step 1: Mechanism of action of N-acetylcysteine (NAC).
NAC is a thiol-containing compound. Its primary mechanism is to serve as a precursor for L-cysteine, which is the rate-limiting substrate for the synthesis of glutathione (GSH) -- the most important intracellular antioxidant. NAC can also directly donate its thiol group to reactive oxygen species (ROS), acting as a direct antioxidant.

Step 2: Primary clinical use -- Paracetamol (acetaminophen) overdose.
In paracetamol toxicity, the toxic metabolite NAPQI depletes hepatic glutathione. NAC replenishes GSH stores, allowing NAPQI to be safely conjugated and excreted. NAC is most effective if given within 8-10 hours of ingestion.

Step 3: Other uses of NAC.

• Mucolytic agent: reduces viscosity of mucus by breaking disulfide bonds in mucoproteins (used in COPD, cystic fibrosis, bronchiectasis)
• Contrast-induced nephropathy prevention (prophylaxis)
• ARDS (adjunctive therapy)

Step 4: Eliminate distractors.
Organophosphate antidote = atropine + pralidoxime. Cyclooxygenase inhibitors = NSAIDs. Benzodiazepine antidote = flumazenil.

Answer: It acts as a precursor for glutathione synthesis