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Questions and Answers
Why is pyridostigmine preferred over neostigmine for chronic management of myasthenia gravis?
Why is pyridostigmine preferred over neostigmine for chronic management of myasthenia gravis?
- It has a faster onset of action.
- It does not act on the NMJ.
- It has a longer duration of action and fewer unwanted muscarinic effects. (correct)
- It is less selective for the NMJ, leading to more muscarinic effects.
Which of the following best describes the mechanism by which organophosphates cause toxicity?
Which of the following best describes the mechanism by which organophosphates cause toxicity?
- Blockage of acetylcholine receptors, preventing neurotransmission.
- Enhancement of acetylcholine metabolism, leading to acetylcholine deficiency.
- Reversible inhibition of acetylcholinesterase, leading to temporary acetylcholine accumulation.
- Irreversible inhibition of acetylcholinesterase, leading to prolonged acetylcholine accumulation. (correct)
A patient presents with miosis, salivation, and muscle fasciculations after exposure to an unknown substance. Which of the following is the MOST likely cause?
A patient presents with miosis, salivation, and muscle fasciculations after exposure to an unknown substance. Which of the following is the MOST likely cause?
- Atropine overdose
- Myasthenia gravis
- Muscarinic receptor antagonism
- Organophosphate poisoning (correct)
Edrophonium is used to diagnose myasthenia gravis. If a patient's muscle weakness temporarily improves after administration of edrophonium, this suggests:
Edrophonium is used to diagnose myasthenia gravis. If a patient's muscle weakness temporarily improves after administration of edrophonium, this suggests:
Which of the following is a key difference between physostigmine and neostigmine regarding their ability to cross the blood-brain barrier (BBB)?
Which of the following is a key difference between physostigmine and neostigmine regarding their ability to cross the blood-brain barrier (BBB)?
A patient with Alzheimer's disease is prescribed a cholinesterase inhibitor to help manage their symptoms. Which of the following medications is MOST likely being used?
A patient with Alzheimer's disease is prescribed a cholinesterase inhibitor to help manage their symptoms. Which of the following medications is MOST likely being used?
Which of the following is the primary mechanism of action of pralidoxime in treating organophosphate poisoning?
Which of the following is the primary mechanism of action of pralidoxime in treating organophosphate poisoning?
A farmer is accidentally exposed to a large amount of organophosphate pesticide. Besides decontamination and support of vital functions, which medication should be administered FIRST?
A farmer is accidentally exposed to a large amount of organophosphate pesticide. Besides decontamination and support of vital functions, which medication should be administered FIRST?
A patient is prescribed echothiophate ophthalmic drops. What condition is this patient MOST likely being treated for?
A patient is prescribed echothiophate ophthalmic drops. What condition is this patient MOST likely being treated for?
Which of the following signs and symptoms are associated with activation of muscarinic receptors in organophosphate poisoning?
Which of the following signs and symptoms are associated with activation of muscarinic receptors in organophosphate poisoning?
Which of the following represents the most critical concern in the management of organophosphate toxicity?
Which of the following represents the most critical concern in the management of organophosphate toxicity?
A patient with a known history of glaucoma is prescribed echothiophate. What is the MOST important consideration when initiating this treatment?
A patient with a known history of glaucoma is prescribed echothiophate. What is the MOST important consideration when initiating this treatment?
A patient presents with muscle weakness. Edrophonium is administered, leading to a brief improvement in strength, followed by a rapid decline below baseline. This pattern suggests:
A patient presents with muscle weakness. Edrophonium is administered, leading to a brief improvement in strength, followed by a rapid decline below baseline. This pattern suggests:
Which characteristic of physostigmine allows it to be effective in treating central nervous system effects of anticholinergic toxicity, unlike other cholinesterase inhibitors?
Which characteristic of physostigmine allows it to be effective in treating central nervous system effects of anticholinergic toxicity, unlike other cholinesterase inhibitors?
What is the primary rationale for using pralidoxime in organophosphate poisoning as early as possible?
What is the primary rationale for using pralidoxime in organophosphate poisoning as early as possible?
Why is the risk of toxicity higher with organophosphate insecticides compared to carbamate insecticides, even though both inhibit acetylcholinesterase?
Why is the risk of toxicity higher with organophosphate insecticides compared to carbamate insecticides, even though both inhibit acetylcholinesterase?
A patient presents with miosis, bronchorrhea, and muscle fasciculations, and a history suggests possible pesticide exposure. After administering atropine, which of the following additional signs would MOST clearly indicate the need for pralidoxime?
A patient presents with miosis, bronchorrhea, and muscle fasciculations, and a history suggests possible pesticide exposure. After administering atropine, which of the following additional signs would MOST clearly indicate the need for pralidoxime?
In a patient undergoing treatment for myasthenia gravis with pyridostigmine, what clinical finding would suggest that the patient is experiencing excessive cholinergic stimulation rather than under treatment?
In a patient undergoing treatment for myasthenia gravis with pyridostigmine, what clinical finding would suggest that the patient is experiencing excessive cholinergic stimulation rather than under treatment?
What is the MOST significant advantage of donepezil over other cholinesterase inhibitors in the treatment of Alzheimer's disease?
What is the MOST significant advantage of donepezil over other cholinesterase inhibitors in the treatment of Alzheimer's disease?
A researcher is studying the effects of different cholinesterase inhibitors on neuromuscular junction activity. Which of the listed drugs would be LEAST likely to have direct effects on nicotinic receptors at the neuromuscular junction (Nm)?
A researcher is studying the effects of different cholinesterase inhibitors on neuromuscular junction activity. Which of the listed drugs would be LEAST likely to have direct effects on nicotinic receptors at the neuromuscular junction (Nm)?
Flashcards
Cholinesterase Inhibitors
Cholinesterase Inhibitors
Drugs that inhibit cholinesterase, increasing acetylcholine levels.
Physostigmine
Physostigmine
A reversible cholinesterase inhibitor that is completely absorbed from the GIT and can pass BBB.
Neostigmine
Neostigmine
A reversible cholinesterase inhibitor that is poorly absorbed from the GIT and cannot pass BBB. It has direct nicotinic action on skeletal muscles (Nm).
Pyridostigmine
Pyridostigmine
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Edrophonium
Edrophonium
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Donepezil
Donepezil
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Organophosphates
Organophosphates
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Organophosphorus Toxicity
Organophosphorus Toxicity
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Edrophonium small doses
Edrophonium small doses
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Organophosphate Poisoning Management
Organophosphate Poisoning Management
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Tensilon Test
Tensilon Test
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Malathione
Malathione
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Echothiophate
Echothiophate
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Atropine
Atropine
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Pralidoxime
Pralidoxime
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Diazepam
Diazepam
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DUMBBELLS
DUMBBELLS
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Nicotinic effects
Nicotinic effects
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Study Notes
Cholinesterase Inhibitors (ChE Is)
- Divided into reversible and irreversible types.
Reversible Cholinesterase Inhibitors
- Includes physostigmine, neostigmine, pyridostigmine, edrophonium, and donepezil.
Irreversible Cholinesterase Inhibitors
- Includes organophosphate compounds like echothiophate.
Physostigmine (Eserine)
- Completely absorbed from the gastrointestinal tract.
- Can cross the blood-brain barrier (BBB).
- Inhibits cholinesterase enzyme, prolonging the effect of endogenous acetylcholine at different sites.
- Does not have a direct effect on cholinergic receptors.
- Used for glaucoma (as a local eye drop) and to counteract atropine overdose.
Neostigmine
- Poorly absorbed from the gastrointestinal tract.
- Cannot cross the BBB.
- Inhibits cholinesterase enzyme similar to physostigmine through a dual mechanism.
- Has a direct nicotinic action on skeletal muscles (Nm).
- Used for myasthenia gravis, paralytic ileus, postoperative urine retention, and to reverse the effects of muscle relaxants like tubocurarine.
Pyridostigmine
- Similar to neostigmine but has slower onset and fewer visceral effects.
- More preferred than neostigmine for chronic treatment of myasthenia gravis.
- Has a more selective action on the neuromuscular junction (NMJ) with fewer unwanted muscarinic effects.
- Offers a longer duration of action.
Edrophonium
- Acts similarly to neostigmine and pyridostigmine but has a short duration of action (5-15 minutes).
- Differentiates between myasthenic crisis and cholinergic crisis in myasthenia patients treated with cholinesterase inhibitors.
- Used in the Tensilon test.
Donepezil
- Reversible cholinesterase inhibitor that selectively inhibits cholinesterase in the central nervous system (CNS), increasing acetylcholine levels in the cerebral cortex.
- Well absorbed after oral administration and crosses the BBB.
- Used to slow the deterioration of cognitive function in Alzheimer's disease.
Tensilon Test
- Small doses of edrophonium improve muscle strength in untreated patients with myasthenia.
- Can worsen muscle weakness if it is due to an excessive dose of AChE inhibitors due to excessive ACh stimulation at the NMJ, resulting in muscle weakness due to maintained depolarization.
Irreversible Cholinesterase Inhibitors: Organophosphorous Compounds
- Types include nerve gases (Sarine, Soman), insecticides (Malathione), and drugs (Echothiophate).
- Due to widespread use as pesticides, responsible accidental and intentional poisonings annually.
- Highly lipid-soluble, effectively absorbed from all sites in body, Including skin.
- Toxicity can occur after dermal or ocular exposure, or after oral ingestion.
- Form a tight, covalent bond with cholinesterase enzyme where strength of the bond increases over time.
- Gradually, AChE becomes irreversibly inhibited.
Clinical Use of Organophosphates
- Echothiophate treats chronic glaucoma that doesn't respond adequately to conservative therapy.
- Provides 24-hour control of intraocular pressure.
- Malathion is used as a pesticide.
- It's also used to treat head lice (pediculosis capitis) as a 0.5% lotion that kills ova and adult lice.
Organophosphorus Toxicity: Etiology
- Accidental exposure to organophosphate pesticides in agricultural and gardening contextes.
- Exposure to chemical warfare agents like soman and sarin.
Organophosphorus Toxicity: Effect
- Organophosphate compounds augment cholinergic neurotransmission in central and peripheral cholinergic synapses.
Organophosphorus Toxicity: Peripheral Cholinergic Synapses Activation
- Muscarinic effects: salivation, lacrimation, miosis, accommodative spasm, bronchoconstriction, intestinal cramps, urinary incontinence.
- Nicotinic effects: skeletal muscle twitches, fasciculation.
Organophosphorus Toxicity: Central Cholinergic Synapses Activation
- Seizures, hallucinations, respiratory depression, coma.
- Main cause of death is respiratory failure.
Organophosphorus Toxicity: Signs
- DUMBBELLS: Diarrhea, Urination, Miosis, Bradycardia, Bronchospasm, Emesis, Lacrimation, Salivation.
Organophosphorus Toxicity: Management
- Decontaminate the patient through gastric lavage and skin wash.
- Support cardiovascular and respiratory function.
- Administer atropine as an acetylcholine receptor antagonist to block excessive ACh and reverse muscarinic effects.
- Administer pralidoxime to regenerate cholinesterase, as soon as possible after exposure.
- Administer diazepam to control convulsions.
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