N-acetylcysteine (NAC) is most effective as an antidote when given within how many hours after overdose?

• A. 24 hours
• B. 8 hours
• C. 48 hours
• D. 72 hours

Answer: (B)

The key idea is that N-acetylcysteine works best when given early, because it replenishes the liver’s glutathione stores needed to detoxify the toxic metabolite NAPQI. In an acetaminophen overdose, glutathione is rapidly depleted as NAPQI accumulates and damages liver cells. Administering NAC promptly supplies sulfhydryl groups and helps restore glutathione quickly, allowing NAPQI to be detoxified before significant hepatocellular injury occurs. This early intervention yields the strongest protection and the best outcomes, which is why within eight hours is the most effective window. Beyond that window, the injury process has often progressed too far for NAC to prevent damage, though it may still offer some benefit in certain cases.