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6# Cholinergic Ag & Antag
1. Nicotinic receptors are directly activated by:
Muscarine
Acetylcholine and nicotine
Pilocarpine only
Atropine
Explanation:
Nicotinic receptors bind acetylcholine and nicotine, causing initial stimulation followed by blockade.
2. Which effect is MOST characteristic of muscarinic receptor activation?
Mydriasis
Tachycardia
Miosis
Bronchodilation
Explanation:
Muscarinic stimulation causes miosis, hypotension, diarrhea, sweating, and urinary urgency.
3. Acetylcholine has very short duration of action because it is:
Rapidly metabolized by cholinesterase
Poorly lipid soluble
Selective for muscarinic receptors
Unable to bind nicotinic receptors
Explanation:
Acetylcholine is rapidly hydrolyzed by acetylcholinesterase (5–30 seconds).
4. Bethanechol is CONTRAINDICATED in:
Atonic bladder
Paralytic ileus
Postoperative urinary retention
Mechanical intestinal obstruction
Explanation:
Bethanechol should NEVER be used in mechanical obstruction due to risk of perforation.
5. Pilocarpine lowers intraocular pressure by:
Decreasing aqueous humor production
Increasing aqueous humor outflow
Blocking beta receptors
Reducing pupil size via alpha blockade
Explanation:
Pilocarpine enhances trabecular outflow of aqueous humor.
6. Pilocarpine is useful in Sjögren syndrome because it:
Increases salivary and lacrimal secretion
Blocks muscarinic receptors
Reduces immune destruction
Decreases glandular inflammation
Explanation:
Pilocarpine stimulates muscarinic receptors in salivary and lacrimal glands.
7. Which cholinesterase inhibitor CANNOT cross the BBB?
Physostigmine
Rivastigmine
Neostigmine
Donepezil
Explanation:
Neostigmine is a quaternary amine and does not enter the CNS.
8. Which drug is used to reverse atropine overdose?
Neostigmine
Pyridostigmine
Edrophonium
Physostigmine
Explanation:
Physostigmine crosses the BBB and reverses central and peripheral antimuscarinic toxicity.
9. Edrophonium is primarily used for:
Chronic treatment of myasthenia gravis
Diagnosis of myasthenia gravis
Reversal of organophosphate poisoning
Alzheimer disease
Explanation:
Edrophonium has a very short duration (10–20 min) and was used diagnostically for MG.
10. Organophosphate poisoning causes death mainly due to:
Respiratory failure
Cardiac arrhythmia
Renal failure
CNS depression only
Explanation:
Respiratory failure occurs due to bronchorrhea, respiratory muscle paralysis, and CNS depression.
11. SLUDGE/DUMBBELSS symptoms indicate poisoning by:
Atropine
Scopolamine
Nicotine
Organophosphates
Explanation:
Organophosphates cause excessive muscarinic stimulation producing SLUDGE/DUMBBELSS toxidrome.
12. Pralidoxime (2-PAM) works by:
Blocking muscarinic receptors
Blocking nicotinic receptors
Reactivating acetylcholinesterase before aging
Preventing acetylcholine release
Explanation:
2-PAM removes the phosphate group from AchE before irreversible aging occurs.
13. Atropine overdose causes hyperthermia because it:
Increases metabolism
Inhibits sweating
Causes vasoconstriction
Stimulates hypothalamus
Explanation:
Atropine blocks sweat glands → inability to dissipate heat.
14. Atropine is CONTRAINDICATED in:
Narrow-angle glaucoma
Sinus bradycardia
Preanesthetic medication
Organophosphate poisoning
Explanation:
Atropine increases intraocular pressure and worsens narrow-angle glaucoma.
15. Scopolamine differs from atropine because it:
Does not cross BBB
Is selective for M1
Causes CNS depression and amnesia
Has no antimuscarinic effects
Explanation:
Scopolamine crosses the BBB more readily, causing sedation and amnesia.
16. Drug of choice for motion sickness prophylaxis is:
Atropine
Ipratropium
Benztropine
Scopolamine
Explanation:
Scopolamine patch is effective when applied before symptom onset.
17. Ipratropium and tiotropium are used in asthma/COPD because they:
Stimulate beta-2 receptors
Block muscarinic receptors in airways
Reduce histamine release
Inhibit acetylcholinesterase
Explanation:
They reduce bronchoconstriction by blocking M3 receptors.
18. Benztropine is useful in Parkinson disease because it:
Reduces acetylcholine activity in CNS
Increases dopamine release
Blocks NMDA receptors
Stimulates muscarinic receptors
Explanation:
Central antimuscarinics restore dopamine–acetylcholine balance in Parkinson disease.
19. Glycopyrrolate differs from atropine because it:
Is lipid soluble
Causes CNS toxicity
Is used for glaucoma
Cannot cross the BBB
Explanation:
Glycopyrrolate is a quaternary amine with no central effects.
20. Muscarinic agonists may cause reflex tachycardia because they:
Stimulate beta-1 receptors
Block M2 receptors
Cause hypotension triggering baroreflex
Increase catecholamine release
Explanation:
Vasodilation → hypotension → compensatory reflex tachycardia.