Anticholinesterase Mechanism and Comparison

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Questions and Answers

What is the primary mechanism of action for anticholinesterases?

Increasing acetylcholine synthesis

Blocking sodium channels

Inhibiting acetylcholinesterase enzyme (correct)

Stimulating acetylcholine receptors directly

Which condition is NOT typically treated with reversible anticholinesterases?

Myasthenia gravis

Alzheimer’s disease

Parkinson’s disease (correct)

Atropine poisoning

What is a common adverse effect associated with cholinomimetic drugs?

Urinary retention

Bradycardia (correct)

Dry mouth

Mydriasis

Which of the following describes the action of organophosphorus compounds in poisoning?

Inhibiting degradation of acetylcholine Signup and view all the answers

Why is atropine used in the management of organophosphorus poisoning?

It counteracts the effects of cholinergic overstimulation Signup and view all the answers

What is the primary action of atropine in the management of organophosphate poisoning?

It blocks the action of acetylcholine on muscarinic receptors. Signup and view all the answers

Which of the following symptoms is NOT associated with muscarinic toxicity from organophosphate poisoning?

Muscle paralysis Signup and view all the answers

What is the 'golden period' for effective reactivation of acetylcholinesterase after organophosphate exposure?

Within 2 hours Signup and view all the answers

Which of the following effects is associated with central nervous system (CNS) toxicity from organophosphate poisoning?

Convulsions Signup and view all the answers

What is the primary role of oximes in the treatment of organophosphate poisoning?

To reactivate acetylcholinesterase Signup and view all the answers

What is the primary origin of Physostigmine?

Natural alkaloid Signup and view all the answers

Which drug is characterized as a quaternary amine?

Neostigmine Signup and view all the answers

What condition is primarily treated with Neostigmine?

Post-operative paralytic ileus Signup and view all the answers

Which cholinomimetic drug is indicated for atropine poisoning?

Physostigmine Signup and view all the answers

Which of the following side effects is associated with cholinomimetics?

Increased sweating Signup and view all the answers

What is the action of organophosphates when they bind to AchE?

They cause irreversible inhibition Signup and view all the answers

What is a common use of Edrophonium?

Diagnosis of myasthenia gravis Signup and view all the answers

Which drug is lipid-soluble and can enter the CNS?

Donepezil Signup and view all the answers

Which of the following is less likely to cause convulsions even at high doses?

Pyridostigmine Signup and view all the answers

Which of the following functions primarily distinguishes Physostigmine from other drugs?

Highly lipid-soluble and CNS penetration Signup and view all the answers

Study Notes

Anticholinesterase Mechanism of Action

Anticholinesterases inhibit acetylcholinesterase (AChE).
This prevents the metabolism of acetylcholine (ACh).
Prolonging ACh action at cholinergic nerve endings.
This leads to accumulation of ACh in the synaptic space.
Reversible anticholinesterases are structurally similar to ACh.
They bind to AChE sites and inhibit its activity temporarily.
Inhibitors indirectly promote cholinergic activity by prolonging ACh duration.

Physostigmine vs. Neostigmine

Physostigmine:
- Natural alkaloid.
- Tertiary amine.
- Highly lipid-soluble.
- Penetrates the blood-brain barrier.
- Used in glaucoma and atropine poisoning.
- Can cause convulsions at high doses.
Neostigmine (and Pyridostigmine):
- Synthetic derivative.
- Quaternary amine.
- Less lipid-soluble.
- Does not readily cross the blood-brain barrier.
- Used in myasthenia gravis, post-operative reversal of muscle relaxation, and atony of the bladder.
- Less likely to induce convulsions than physostigmine.

Therapeutic Uses of Reversible Anticholinesterases

Alzheimer's disease:
- Galantamine
- Tacrine
- Donepezil
- Rivastigmine

Organophosphate Poisoning & Management

Initial treatment:
- Rapid Decontamination
- Maintain Respiration
- Suction of bronchial secretions
- Maintain intravenous line
- Catheterize the urinary bladder
- Control convulsions.
Drugs:
- Atropine: Antimuscarinic agent, blocks ACh actions on muscarinic receptors in both central and peripheral nervous systems.
- Oximes (e.g., pralidoxime, obidoxime): Cholinesterase reactivators, given within 2 hours after exposure to reactivate inhibited acetylcholinesterase.

Adverse Effects of Cholinergic Drugs

Salivation, lacrimation, urination, diaphoresis (sweating), and defecation.
Gastrointestinal upset (e.g., nausea, vomiting).
CNS stimulation.
Miosis (constriction of pupils).
Bronchoconstriction and tracheobronchial secretions.
AV block (atrioventricular block).

Drugs Used in Glaucoma

Parasympathetic agents (e.g., pilocarpine, physostigmine).
Adrenergic agonists (e.g., dipivefrin, apraclonidine, brimonidine).
Beta blockers (e.g., timolol, levobunolol, carteolol).
Carbonic anhydrase inhibitors (e.g., acetazolamide, dorzolamide).
Prostaglandin analogs (e.g., latanoprost, travoprost).
Osmotic agents (e.g., mannitol, glycerin).

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Description

This quiz explores the mechanism of action of anticholinesterases and compares physostigmine with neostigmine. Understand how these compounds interact with acetylcholine and their clinical applications. Test your knowledge on their differences in solubility and effects on the nervous system.