Which drug is similar to atropine but lasts twice as long (2-4 hours) and is more expensive, working better on rabbits than atropine?

• A. Propantheline
• B. Glycopyrrolate
• C. Norepinephrine
• D. Isoproterenol

Answer: (B)

Antimuscarinic drugs that block acetylcholine at muscarinic receptors can substitute for atropine, but the one that lasts longer and is often favored when a longer window of anticholinergic effect is needed is a quaternary ammonium antimuscarinic. This type, like glycopyrrolate, behaves much like atropine in blocking muscarinic receptors, but its quaternary structure keeps it in the periphery with minimal brain penetration, so it offers effective bradycardia and secretions control with fewer central side effects. Its duration is longer—typically around the 2–4 hour range—and it tends to be more expensive. In rabbits, glycopyrrolate often provides a more reliable peripheral anticholinergic effect than atropine, which is why it’s favored in that species.

Other options don’t fit as well. Propantheline is another antimuscarinic but isn’t consistently chosen for longer duration in comparison to glycopyrrolate, and it can have more CNS effects because it’s less restricted to the periphery. The remaining two are adrenergic agents, not antimuscarinics, so they act through entirely different mechanisms and wouldn’t be described as similar to atropine.