Question

Antidote for paracetamol poisoning is ________.

• A. N-acetylcysteine
• B. naloxone
• C. atropine
• D. protamine

Hint:

Paracetamol Antidote Rule: Administer $N$-acetylcysteine (NAC) early (ideally within 8–10 hours of ingestion) to replenish glutathione stores and prevent severe hepatic necrosis.

Answer 1

The Correct Option is A

Concept: At therapeutic doses, paracetamol (acetaminophen) is safely metabolized via glucuronidation and sulfation pathways. A minor fraction is converted by CYP2E1 into a highly reactive, toxic electrophilic intermediate called NAPQI ($N$-acetyl-$p$-benzoquinone imine), which is rapidly neutralized by combining with endogenous hepatic glutathione. In a paracetamol overdose, the normal metabolic pathways become saturated, leading to excessive production of NAPQI. This depletes hepatic glutathione stores, allowing NAPQI to bind covalently to vital proteins in hepatocytes and cause acute hepatic necrosis.

Step 1: Evaluate the mechanism of the antidote.
$N$-acetylcysteine (NAC) acts as an effective antidote through two key mechanisms:
• It serves as a direct precursor for glutathione synthesis, replenishing hepatic glutathione stores.
• It can bind directly to reactive NAPQI, neutralizing its toxicity and protecting hepatocytes from oxidative damage.

Step 2: Verify alternative options.
* Naloxone is a competitive opioid receptor antagonist used to reverse opioid overdose. * Atropine is an anticholinergic drug used to treat organophosphate poisoning or bradycardia. * Protamine sulfate is the specific chemical antidote used to neutralize heparin overdosage.