Reversible inhibitors – Physostigmine MCQs With Answer

Reversible inhibitors – Physostigmine MCQs With Answer

Physostigmine is a classic reversible cholinesterase inhibitor widely discussed in B.Pharm pharmacology. This focused introduction and MCQ set covers physostigmine’s mechanism of action, carbamate chemistry, pharmacokinetics, central nervous system penetration, therapeutic uses (notably anticholinergic toxicity), adverse effects, contraindications and comparisons with agents like neostigmine and pyridostigmine. Emphasis is placed on clinical application, monitoring, dosing principles and emergency management to prepare B.Pharm students for exams and clinical decision-making. Keywords: reversible inhibitors, physostigmine, acetylcholinesterase inhibitor, cholinesterase inhibitors, anticholinesterase, pharmacology, B.Pharm, therapeutic uses, adverse effects. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which class of enzyme does physostigmine primarily inhibit?

• Monoamine oxidase
• Acetylcholinesterase
• Butyrylcholinesterase only
• Phosphodiesterase

Correct Answer: Acetylcholinesterase

Q2. Physostigmine belongs to which chemical subclass of cholinesterase inhibitors?

• Organophosphates
• Carbamates
• Alkaloid steroids
• Oximes

Correct Answer: Carbamates

Q3. What property of physostigmine allows it to reverse central anticholinergic symptoms?

• Strong plasma protein binding
• Quaternary ammonium structure
• Tertiary amine structure enabling blood–brain barrier penetration
• High renal excretion unchanged

Correct Answer: Tertiary amine structure enabling blood–brain barrier penetration

Q4. Which clinical indication is physostigmine most commonly used for?

• First-line treatment of myasthenia gravis
• Treatment of anticholinergic (e.g., atropine) toxicity
• Maintenance therapy for Alzheimer’s disease
• Treatment of organophosphate poisoning

Correct Answer: Treatment of anticholinergic (e.g., atropine) toxicity

Q5. How does physostigmine inhibit acetylcholinesterase at the molecular level?

• Irreversible phosphorylation of the active site serine
• Competitive antagonism at muscarinic receptors
• Carbamylation of the active site serine causing reversible inhibition
• Oxidative degradation of acetylcholine

Correct Answer: Carbamylation of the active site serine causing reversible inhibition

Q6. Compared to organophosphates, physostigmine’s inhibition of AChE is:

• Completely irreversible
• Noncompetitive and permanent
• Reversible with shorter duration
• Dependent on glutathione depletion

Correct Answer: Reversible with shorter duration

Q7. Which of the following is a central adverse effect of physostigmine at high doses?

• Insomnia
• Seizures
• Hyperglycemia
• Peripheral neuropathy

Correct Answer: Seizures

Q8. Physostigmine is contraindicated or used with extreme caution in which condition due to risk of arrhythmia?

• Uncontrolled glaucoma
• Tricyclic antidepressant (TCA) overdose without monitoring
• Hypothyroidism
• Diabetes mellitus

Correct Answer: Tricyclic antidepressant (TCA) overdose without monitoring

Q9. Which physiological effect is expected after therapeutic dosing of physostigmine?

• Tachycardia and dry mouth
• Miosis and increased salivation
• Hyperthermia and urinary retention
• Mydriasis and constipation

Correct Answer: Miosis and increased salivation

Q10. Which statement correctly contrasts physostigmine with neostigmine?

• Physostigmine is quaternary and does not cross the BBB; neostigmine is tertiary and crosses the BBB
• Both cross the BBB equally
• Physostigmine is tertiary and crosses the BBB; neostigmine is quaternary and does not cross the BBB
• Neostigmine is irreversible while physostigmine is irreversible as well

Correct Answer: Physostigmine is tertiary and crosses the BBB; neostigmine is quaternary and does not cross the BBB

Q11. What is the usual route of administration for physostigmine in acute anticholinergic toxicity?

• Oral tablet only
• Intravenous slow injection under monitoring
• Topical application
• Inhalational aerosol

Correct Answer: Intravenous slow injection under monitoring

Q12. Physostigmine’s duration of action is generally in the range of:

• 12–24 hours
• 30–60 minutes
• 3–5 days
• 24–48 hours

Correct Answer: 30–60 minutes

Q13. Which monitoring parameter is most important when administering physostigmine IV for severe anticholinergic toxicity?

• Blood glucose
• Electrocardiogram (ECG) and cardiac rhythm
• Liver function tests
• Serum calcium

Correct Answer: Electrocardiogram (ECG) and cardiac rhythm

Q14. Which of the following best explains why physostigmine can reverse central delirium caused by anticholinergics?

• It blocks dopamine receptors in the CNS
• It increases central acetylcholine by inhibiting acetylcholinesterase
• It acts as a benzodiazepine receptor agonist
• It directly antagonizes histamine H1 receptors

Correct Answer: It increases central acetylcholine by inhibiting acetylcholinesterase

Q15. Physostigmine is metabolized primarily by:

• Renal tubular secretion unchanged
• Plasma and hepatic esterases
• CYP3A4-mediated oxidation only
• Glucuronidation exclusively

Correct Answer: Plasma and hepatic esterases

Q16. Which sign indicates an adequate therapeutic response to physostigmine in anticholinergic poisoning?

• Worsening hyperthermia
• Resolution of delirium and decreased agitation
• Development of urinary retention
• Onset of severe diarrhea immediately

Correct Answer: Resolution of delirium and decreased agitation

Q17. Which of the following is a classic peripheral muscarinic effect of physostigmine?

• Bronchodilation
• Decreased bowel motility
• Bradycardia
• Dry skin

Correct Answer: Bradycardia

Q18. In which neurological disorder is physostigmine NOT typically used as maintenance therapy?

• Alzheimer’s disease maintenance therapy
• Acute anticholinergic toxicity
• Diagnostic challenge tests historically
• Occasional ototoxicity management (not an indication)

Correct Answer: Alzheimer’s disease maintenance therapy

Q19. Which statement about physostigmine’s effect on neuromuscular junction is true?

• It selectively blocks nicotinic receptors at the NMJ
• It increases acetylcholine levels and can enhance neuromuscular transmission
• It irreversibly desensitizes the endplate to acetylcholine
• It has no effect on peripheral neuromuscular transmission

Correct Answer: It increases acetylcholine levels and can enhance neuromuscular transmission

Q20. Which adverse effect should be anticipated if physostigmine is accidentally overdosed?

• Anticholinergic crisis
• Cholinergic crisis with bronchorrhea and bronchospasm
• Purely hepatic necrosis
• Hypernatremia

Correct Answer: Cholinergic crisis with bronchorrhea and bronchospasm

Q21. Which agent is the antidote for muscarinic effects in physostigmine-induced cholinergic toxicity?

• Propranolol
• Atropine
• Pralidoxime only
• Flumazenil

Correct Answer: Atropine

Q22. Why is physostigmine sometimes preferred over neostigmine for central anticholinergic toxicity?

• Physostigmine has longer duration than neostigmine
• Physostigmine is cheaper and more available
• Physostigmine crosses the blood–brain barrier and reverses central effects
• Neostigmine causes irreversible inhibition of AChE

Correct Answer: Physostigmine crosses the blood–brain barrier and reverses central effects

Q23. Which ECG change may be associated with physostigmine administration in susceptible patients?

• Prolonged QT leading to torsades only
• Complete heart block or bradyarrhythmias
• ST-elevation myocardial infarction pattern always
• New left bundle branch block only

Correct Answer: Complete heart block or bradyarrhythmias

Q24. What precaution is essential before giving physostigmine to a patient with suspected TCA overdose?

• No precautions are needed
• Ensure continuous cardiac monitoring and be prepared for arrhythmias
• Give large bolus doses rapidly to avoid complications
• Avoid measuring electrolytes

Correct Answer: Ensure continuous cardiac monitoring and be prepared for arrhythmias

Q25. Which population requires extra caution when using physostigmine due to increased sensitivity to cholinergic effects?

• Young healthy adults only
• Patients with asthma or COPD
• Patients with hyperthyroidism only
• Individuals with lactose intolerance

Correct Answer: Patients with asthma or COPD

Q26. Which effect on pupil size would you expect after physostigmine administration?

• Mydriasis (pupil dilation)
• Miosis (pupil constriction)
• No change in pupil size
• Pupillary irregularity without constriction or dilation

Correct Answer: Miosis (pupil constriction)

Q27. Which lab test can be used to assess exposure to cholinesterase inhibitors in general?

• Serum amylase only
• Plasma (butyryl) cholinesterase and red blood cell acetylcholinesterase activity
• Serum creatinine kinase only
• Thyroid function tests

Correct Answer: Plasma (butyryl) cholinesterase and red blood cell acetylcholinesterase activity

Q28. Which of the following is a major peripheral muscarinic sign to monitor after physostigmine therapy?

• Hyporeflexia
• Excessive bronchial secretions and bronchospasm
• Persistent hyperglycemia
• Loss of deep tendon reflexes

Correct Answer: Excessive bronchial secretions and bronchospasm

Q29. Which feature differentiates carbamate inhibitors like physostigmine from irreversible organophosphate inhibitors?

• Carbamates cause permanent enzyme phosphorylation
• Carbamate-inhibited AChE undergoes spontaneous decarbamylation restoring activity sooner
• Carbamates only inhibit butyrylcholinesterase
• Organophosphates are rapidly reversible without oximes

Correct Answer: Carbamate-inhibited AChE undergoes spontaneous decarbamylation restoring activity sooner

Q30. Which of the following is NOT a common adverse effect of physostigmine?

• Nausea and vomiting
• Excessive salivation
• Hypertension crises as a typical effect
• Bradycardia

Correct Answer: Hypertension crises as a typical effect

Q31. Which drug would most likely have an additive bradycardic effect if given with physostigmine?

• Atropine
• Beta-blocker (e.g., metoprolol)
• Neostigmine
• Vitamin C

Correct Answer: Beta-blocker (e.g., metoprolol)

Q32. Why must physostigmine be titrated carefully in elderly patients?

• Elderly have increased hepatic metabolism reducing effects
• Increased sensitivity to cholinergic effects and cardiac conduction disturbances
• Elderly are resistant to muscarinic side effects
• It causes severe hyperactivity in elderly patients

Correct Answer: Increased sensitivity to cholinergic effects and cardiac conduction disturbances

Q33. Which of the following is a correct statement regarding physostigmine’s role in organophosphate poisoning?

• Physostigmine is the first-line antidote for organophosphate poisoning
• Physostigmine is generally not used; pralidoxime and atropine are preferred
• Physostigmine permanently reactivates phosphorylated AChE
• Physostigmine increases organophosphate toxicity

Correct Answer: Physostigmine is generally not used; pralidoxime and atropine are preferred

Q34. Which symptom would suggest progression from therapeutic effect to cholinergic toxicity after physostigmine?

• Reduction in secretions
• Development of muscle weakness and fasciculations
• Improved mental status without other signs
• Dry mouth and constipation

Correct Answer: Development of muscle weakness and fasciculations

Q35. Which agent is a longer-acting carbamate used for myasthenia gravis, often compared with physostigmine?

• Pyridostigmine
• Propranolol
• Atropine
• Pralidoxime

Correct Answer: Pyridostigmine

Q36. Which statement about physostigmine and blood–brain barrier is correct?

• Physostigmine is unable to cross the blood–brain barrier due to high polarity
• Physostigmine crosses the blood–brain barrier because it is a tertiary amine
• All cholinesterase inhibitors cross the BBB equally
• Crossing the BBB is unrelated to amine type

Correct Answer: Physostigmine crosses the blood–brain barrier because it is a tertiary amine

Q37. Which of the following clinical signs would indicate excessive central cholinergic stimulation after physostigmine?

• Agitation and psychosis
• Confusion progressing to seizures
• Loss of taste only
• Peripheral neuropathy

Correct Answer: Confusion progressing to seizures

Q38. In a patient with pseudocholinesterase deficiency, physostigmine administration is expected to:

• Have no clinical effect
• Possibly prolong action of drugs like succinylcholine and increase cholinergic load
• Cure the deficiency permanently
• Only increase renal excretion of succinylcholine

Correct Answer: Possibly prolong action of drugs like succinylcholine and increase cholinergic load

Q39. Which of these drugs is a non-carbamate reversible acetylcholinesterase inhibitor used for Alzheimer’s disease (for comparison)?

• Donepezil
• Neostigmine
• Pyridostigmine
• Physostigmine only

Correct Answer: Donepezil

Q40. Which monitoring is advisable after physostigmine administration in a patient with severe anticholinergic effects?

• Hourly liver enzymes only
• Continuous cardiac monitoring and respiratory observation
• No monitoring required
• Daily lipid profile

Correct Answer: Continuous cardiac monitoring and respiratory observation

Q41. Which contraindication is most appropriate for physostigmine use?

• Confirmed mechanical intestinal obstruction
• Mild seasonal allergies
• Controlled hypertension
• History of migraine without aura

Correct Answer: Confirmed mechanical intestinal obstruction

Q42. Which of the following best describes physostigmine’s onset of action when given IV?

• Onset within 1–2 minutes
• Onset after 24 hours
• Delayed onset of 6–8 hours
• No systemic onset expected

Correct Answer: Onset within 1–2 minutes

Q43. Which sign differentiates anticholinergic toxicity from cholinergic toxicity clinically?

• Anticholinergic: dry skin; cholinergic: wet skin and hypersalivation
• Anticholinergic: excessive salivation; cholinergic: dry skin
• Both present with identical secretory signs
• Anticholinergic causes miosis, cholinergic causes mydriasis

Correct Answer: Anticholinergic: dry skin; cholinergic: wet skin and hypersalivation

Q44. Which dosage principle is important when administering physostigmine to reverse anticholinergic delirium?

• Administer a single large bolus dose without titration
• Start with small incremental doses and titrate to clinical effect
• Give oral doses only to maximize safety
• Use only in outpatient settings

Correct Answer: Start with small incremental doses and titrate to clinical effect

Q45. Which of the following adverse effects is most likely to require immediate treatment following physostigmine overdose?

• Mild headache
• Severe bronchospasm with hypoxia
• Transient skin flushing
• Temporary blurred vision that resolves

Correct Answer: Severe bronchospasm with hypoxia

Q46. Which agent is indicated to reactivate phosphorylated acetylcholinesterase in organophosphate poisoning (contrast therapy)?

• Atropine only
• Pralidoxime (2-PAM)
• Physostigmine
• Propranolol

Correct Answer: Pralidoxime (2-PAM)

Q47. When teaching B.Pharm students the pharmacodynamics of physostigmine, which receptor family effects should be emphasized?

• Adrenergic alpha and beta only
• Muscarinic and nicotinic receptors due to increased acetylcholine
• GABA-A receptors exclusively
• Histamine H2 receptors mainly

Correct Answer: Muscarinic and nicotinic receptors due to increased acetylcholine

Q48. Which clinical scenario warrants immediate administration of physostigmine after confirming anticholinergic toxicity?

• Mild dry mouth without CNS effects
• Severe agitation, hallucinations and life-threatening delirium from anticholinergic agents
• Stable patient with chronic constipation only
• Asymptomatic exposure with normal vitals

Correct Answer: Severe agitation, hallucinations and life-threatening delirium from anticholinergic agents

Q49. Which feature of physostigmine distinguishes it pharmacologically from atropine?

• Physostigmine is a muscarinic receptor antagonist; atropine is an AChE inhibitor
• Physostigmine increases acetylcholine by inhibiting AChE; atropine blocks muscarinic receptors
• Both have identical mechanisms of action
• Atropine increases AChE activity while physostigmine blocks acetylcholine receptors

Correct Answer: Physostigmine increases acetylcholine by inhibiting AChE; atropine blocks muscarinic receptors

Q50. Which teaching point is most important for B.Pharm students regarding physostigmine use in clinical practice?

• It can be given freely without monitoring because it is safe
• It requires careful dosing, monitoring for cholinergic crisis, and readiness to treat arrhythmias and bronchospasm
• It should replace atropine in all poisonings
• It is an antibiotic with no cholinergic effects

Correct Answer: It requires careful dosing, monitoring for cholinergic crisis, and readiness to treat arrhythmias and bronchospasm

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com