Parasympathomimetic Agents

  • Parasympathomimetic agents are drugs that mimic the actions of acetylcholine (ACh) on parasympathetic nervous system
  • Parasympathomimetic agents
  • These agents stimulate cholinergic receptors, resulting in increased secretions, smooth muscle contraction, slowed heart rate, and other parasympathetic effects.
  • They are classified into two main groups:
    • Direct-acting cholinergic agonists
    • Indirect-acting cholinesterase inhibitors
  • A third category includes cholinesterase reactivators, used to reverse irreversible inhibition of acetylcholinesterase.

SAR of Parasympathomimetic Agents

  • Direct Acting Parasympathomimetics (Cholinergic Agonists)
    1. Quaternary ammonium group is essential for activity.
    2. The size of the alkyl groups on the nitrogen should not exceed a methyl group for optimal activity.
    3. Ester group is required for muscarinic activity; modification affects hydrolysis rate and selectivity.
    4. The distance between the nitrogen and the oxygen (O–C–C–N) must remain two-carbon units (ideal).
    5. β-methyl substitution enhances selectivity for muscarinic receptors and resists hydrolysis by cholinesterase.
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Examples:

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