22 Questions
Which of the following is a characteristic of M2 receptors in the CNS?
Inhibitory
What is the effect of M3 receptors on the smooth muscles?
Contraction
Which of the following is a cholinomimetic that acts directly on cholinergic receptors?
Bethanechol
What is the effect of M3 receptors on the eye?
Miosis
Which of the following is a classification of cholinomimetics?
Direct and Indirect
What is the effect of M2 receptors on the heart?
Decreased heart rate
What is the mechanism of action of cholinesterase inhibitors?
Inhibition of acetylcholinesterase
What is the effect of M3 receptors on exocrine glands?
Increased secretion
What is the primary therapeutic use of Pilocarpine?
Treatment of dry eye and mouth
Which of the following is a therapeutic use of Neostigmine?
Treatment of post-operative paralytic ileus and urinary retention
What is the primary mechanism of action of Cholinomimetics?
Stimulation of muscarinic receptors
What is the primary difference between 3ry Amines and 4ry Amines?
Lipophilicity
What is the antidote for competitive NMBs?
Neostigmine
What is the primary adverse effect of cholinomimetics on the CNS?
Irritability and convulsions
What is the characteristic of Neostigmine in terms of its absorption?
Poorly absorbed, does not cross BBB and conjunctiva
What is the primary therapeutic use of Physostigmine?
Treatment of atropine toxicity
What is the primary difference between Muscarinic and Nicotinic receptors?
Function
Which of the following Cholinesterase Inhibitors is used to antagonize central and peripheral effects of atropine?
Physostigmine
What is the effect of Cholinesterase Inhibitors on skeletal muscle power?
Increase skeletal muscle power
What is the characteristic of Irreversible Cholinesterase Inhibitors?
They are highly lipid soluble and absorbed from all sites of the body
What is the primary effect of Physostigmine on the eye?
Miotic effect
Which of the following Cholinesterase Inhibitors is an analogue of Neostigmine with a longer duration of action and fewer visceral side effects?
Pyridostigmine
Study Notes
Choline Esterase Inhibitors
- Reversible inhibitors: Edrophonium (ultra-short acting), Neostigmine (intermediate acting), and Pyridostigmine (long-acting)
- Irreversible inhibitors: Organophosphates, which are highly lipid soluble and absorbed from all sites of the body, even skin
Mechanism of Action
- Cholinesterase inhibitors bind to the enzyme acetylcholinesterase, preventing the breakdown of acetylcholine
- This leads to an increase in acetylcholine levels, enhancing neurotransmission at cholinergic synapses
Muscarinic Effects
- M2 receptors: inhibitory in CNS, slow heart rate, and decrease contractility
- M3 receptors:
- Smooth muscle contraction
- Bronchospasm
- GIT and urinary bladder contraction
- Eye: miosis, accommodation, and increased aqueous drainage
- Exocrine glands: increased secretion
- Vascular endothelium: NO release, vasodilation, and decreased blood pressure
Classification of Cholinomimetics
- Directly acting: Choline esters, Natural alkaloids
- Indirectly acting: Reversible and irreversible inhibitors
Therapeutic Uses of Cholinomimetics
- 3ry Amines:
- Hair tonic: Pilocarpine
- Alzheimer's disease: Donepezil and Rivastagmine
- Atropine toxicity: Physostigmine
- Dry eye and mouth: Pilocarpine and Cevemiline
- Miotics in glaucoma: Pilocarpine and Physostigmine
- 4ry Amines:
- Post-operative: Neostigmine and Bethanechol
- Megacolon/prokinetic: Bethanechol
- Myasthenia gravis: Pyridostigmine
- Antidote for competitive NMBs: Neostigmine
- Diagnosis of Myasthenia gravis: Edrophonium (ultra-short acting)
Adverse Effects and Contraindications
- CNS: Irritability, convulsions
- Eye: Miosis, lid twitches, brow ache, and frontal headache
- Exocrine: Lacrimation, salivation, and increased HCl secretion
- CVS: Bradycardia, hypotension, cardiac arrest, and infarction
- Respiratory: Bronchospasm and increased secretion
- GI: Urination, diarrhea, colic, nausea, and vomiting
- Muscular: Fasciculations and paralysis in toxic doses
Learn about the different types of cholinesterase inhibitors, including reversible and irreversible inhibitors, and their mechanisms of action.
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