- Clinical science
Parasympathomimetic drugs (Cholinomimetic drugs)
Summary
Parasympathomimetic drugs activate the parasympathetic nervous system (PSNS). As the neurotransmitter of the PSNS is acetylcholine, parasympathomimetics are also called cholinomimetic agents. These are classified according to whether they act as direct agonists of acetylcholine receptors (ACh) or indirect agonists of ACh (also called anticholinesterase). While direct agonists act by binding directly to muscarinic or nicotinic ACh receptors, indirect agonists prolong the action of endogenous acetylcholine by inhibiting acetylcholinesterase. Direct agonists of ACh are used topically in ophthalmology to induce miosis, while indirect agonists are used to treat, e.g., postoperative ileus or urinary retention and myasthenia gravis.
Overview
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Mechanism of action
- Direct parasympathomimetics: bind to muscarinic or nicotinic ACh receptors
- Indirect parasympathomimetics: inhibit acetylcholine esterase
Drug | Indications |
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Direct parasympathomimetics (direct agonist) | |
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Indirect parasympathomimetics (indirect agonist) | |
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Effects
Effects of parasympathomimetics
ACh receptors | Organ/Tissue | Effects |
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M1, M4, M5 |
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M2 | ||
M3 |
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Nicotinic | Skeletal muscle |
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References:[1]
Side effects
Direct parasympathomimetics
- Local side effects (e.g., application to eyes: blurred vision due to miosis)
- If applied systemically: side effects identical to those of indirect parasympathomimetics
Indirect parasympathomimetics
- Cardiovascular symptoms: bradycardia, hypotension
- Gastrointestinal symptoms: ↑ salivation, diarrhea, abdominal pain, uncontrolled urination
- Increased sweating, salivation, and gastric secretion
- Nausea
- Ocular symptoms: miosis, lacrimation
- CNS-related symptoms: restlessness, anxiety, ataxia, tremor possibly culminating in coma
- Musculoskeletal symptoms: fasciculations, weakness; , spasms, paralysis → peripheral neuromuscular respiratory failure
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Cholinergic crisis (cholinergic syndrome)
- Cause: in most cases as a result of poisoning with organophosphates
- Clinical presentation: severe and life-threatening constellation of side effects of indirect parasympathomimetics
- Antidotes: antimuscarinic agents atropine, pralidoxime
DUMBBELLSS for clinical features of cholinergic syndrome = Diarrhea, Urination, Miosis, Bronchospasm, Bradycardia, Emesis, Lacrimation, Lethargy, Sweating, and Salivation!
References:[2]
We list the most important adverse effects. The selection is not exhaustive.