Which drug is explicitly described as a cholinesterase reactivator?

• A. Isoproterenol
• B. Pralidoxime
• C. Norepinephrine
• D. Phenylephrine

Answer: (B)

Cholinesterase reactivators are used to reverse organophosphate- or nerve agent–induced inhibition of acetylcholinesterase by cleaving the bond between the enzyme and the inhibitor, thereby restoring the enzyme’s activity. Pralidoxime directly binds to the phosphorylated enzyme and removes the phosphate group, regenerating active acetylcholinesterase. Its effectiveness depends on avoiding aging of the enzyme–inhibitor complex, and it is typically used alongside atropine to counter muscarinic symptoms.

The other drugs listed are sympathomimetic agents that act on adrenergic receptors to raise blood pressure or heart rate; they do not restore acetylcholinesterase activity.