Rx Insights: Ganglionic Stimulants (Non-Selective / Muscarinic Agonists)

Introduction:

1. Non-selective or muscarinic agonists are drugs that stimulate both muscarinic and nicotinic receptors of the parasympathetic nervous system. 

2. They mimic the effects of acetylcholine (ACh) and are therefore called cholinergic agonists. 

3. These agents act directly on cholinergic receptors present in smooth muscles, cardiac tissue, and glands. 

4. By stimulating muscarinic receptors, they enhance parasympathetic activity, leading to effects such as bradycardia, miosis, and increased glandular secretion. 

5. At nicotinic sites in autonomic ganglia, they cause ganglionic stimulation, affecting both sympathetic and parasympathetic tone. 

6. Examples include acetylcholine, carbachol, and nicotine (in small doses). 

7. Their actions are short-lived due to rapid degradation by cholinesterase enzymes. 

8. Therapeutically, they are rarely used because of widespread and unpredictable effects. 

9. However, they are valuable in experimental pharmacology for studying autonomic nervous system function. 

10. Overstimulation can cause toxicity, presenting with salivation, sweating, bronchospasm, and hypotension.

 Rx Insights: Ganglionic Stimulants (Non-Selective / Muscarinic Agonists)

💊 Drug Class: 

Cholinergic agonists that stimulate both muscarinic and nicotinic receptors, leading to widespread parasympathomimetic and sympathomimetic effects.

🧬 Mechanism of Action: 

Directly activate acetylcholine receptors (both muscarinic and nicotinic). 

Cause depolarization of post-ganglionic neurons in both the sympathetic and parasympathetic ganglia. 

Responses depend on which system predominates in the target organ (e.g., parasympathetic in heart, sympathetic in blood vessels).

💊 Examples: 

Acetylcholine (ACh) — prototype, acts on both M and N receptors 

Carbachol — strong nicotinic and muscarinic agonist 

Nicotine (in low dose) — stimulates ganglia before desensitization 

Pilocarpine — mainly muscarinic, but has some ganglionic effects

✅ Therapeutic Uses: 

Carbachol: for glaucoma (reduces intraocular pressure) 

Pilocarpine: for xerostomia (dry mouth), glaucoma 

Nicotine (controlled forms): in smoking cessation 

Experimental: to study autonomic ganglionic transmission

⚠️ Adverse Effects: 

Cardiovascular: bradycardia, hypotension (parasympathetic) 

Gastrointestinal: nausea, vomiting, diarrhea, abdominal cramps 

Respiratory: bronchoconstriction, ↑ bronchial secretions 

Other: salivation, sweating, lacrimation, urinary urgency

🚫 Contraindications: 

Asthma / COPD (due to bronchoconstriction) 

Peptic ulcer disease (↑ acid secretion) 

Coronary artery disease (risk of hypotension/bradycardia) 

Parkinson’s disease (may worsen tremor)

💊 Major Drug Interactions: 

1. Beta-blockers → additive bradycardia, hypotension

2. Anticholinergics (e.g., atropine) → antagonize effects

3. Tricyclic antidepressants / antihistamines → reduce muscarinic stimulation

💡 Clinical Tips: 

Monitor HR, BP, and respiratory status when used therapeutically. 

Systemic use is limited due to widespread side effects. 

Topical formulations (like eye drops) are preferred for local effects. 

Overstimulation may progress to ganglionic blockade and respiratory failure.

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