Reversible inhibitors – Edrophonium chloride MCQs With Answer

Introduction: Edrophonium chloride is a short-acting, reversible acetylcholinesterase inhibitor widely studied in B.Pharm pharmacology. This water-soluble, quaternary ammonium compound produces rapid onset and brief duration of action, making it useful for diagnostic applications such as the Tensilon test in suspected myasthenia gravis and for differentiating myasthenic from cholinergic crisis. Key learning areas include mechanism of reversible inhibition, pharmacokinetics, clinical uses, adverse effects, drug interactions, and comparison with other AChE inhibitors like neostigmine and physostigmine. These MCQs emphasize conceptual understanding and clinical relevance for exam preparation. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which description best characterizes edrophonium chloride?

• Long-acting irreversible acetylcholinesterase inhibitor
• Short-acting reversible acetylcholinesterase inhibitor
• Muscarinic receptor antagonist
• Depolarizing neuromuscular blocker

Correct Answer: Short-acting reversible acetylcholinesterase inhibitor

Q2. The primary clinical diagnostic use of edrophonium is:

• Treatment of Alzheimer’s disease
• Treatment of Parkinson’s disease
• Tensilon test for myasthenia gravis
• Maintenance therapy for asthma

Correct Answer: Tensilon test for myasthenia gravis

Q3. Edrophonium’s mechanism of acetylcholinesterase inhibition is best described as:

• Covalent phosphorylation of the active site
• Noncovalent, reversible binding at the active site
• Irreversible carbamylation of enzyme
• Allosteric inhibition of nicotinic receptors

Correct Answer: Noncovalent, reversible binding at the active site

Q4. Which structural feature of edrophonium limits its ability to cross the blood–brain barrier?

• Lipophilic aromatic ring
• Quaternary ammonium group
• High lipid solubility
• Neutral polar surface

Correct Answer: Quaternary ammonium group

Q5. Typical onset and duration of edrophonium effect after IV administration are:

• Onset 30–60 min, duration 6–8 hours
• Onset 5–15 sec, duration 1–2 min
• Onset 30–60 sec, duration 5–15 min
• Onset 4–6 hours, duration 24 hours

Correct Answer: Onset 30–60 sec, duration 5–15 min

Q6. Which adverse effect is most likely after edrophonium administration?

• Hypertension and tachycardia
• Cholinergic bradycardia and increased secretions
• Excessive sedation due to CNS penetration
• Peripheral neuropathy

Correct Answer: Cholinergic bradycardia and increased secretions

Q7. Edrophonium is most useful for distinguishing between:

• Asthma and COPD
• Myasthenic crisis and cholinergic crisis
• Parkinsonian and essential tremor
• Type 1 and type 2 diabetes

Correct Answer: Myasthenic crisis and cholinergic crisis

Q8. Compared to neostigmine, edrophonium has:

• Longer duration and stronger covalent binding
• Shorter duration and purely electrostatic binding
• Greater CNS penetration
• Irreversible enzyme inhibition

Correct Answer: Shorter duration and purely electrostatic binding

Q9. Which precaution is essential when performing an edrophonium (Tensilon) test?

• No monitoring required because it is harmless
• Have atropine and resuscitation equipment ready
• Administer a full bolus without observation
• Ensure the patient is fully supine and fasting

Correct Answer: Have atropine and resuscitation equipment ready

Q10. The binding site of edrophonium on acetylcholinesterase is primarily:

• Covalent serine residue modification
• Anionic site with electrostatic attraction
• Peripheral site causing allosteric change
• Nicotinic receptor binding pocket

Correct Answer: Anionic site with electrostatic attraction

Q11. In the Tensilon test, a transient improvement after edrophonium suggests:

• Myasthenic weakness due to reduced ACh release
• Myasthenia gravis due to increased neuromuscular transmission
• Primary muscle disease like muscular dystrophy
• Peripheral neuropathy

Correct Answer: Myasthenia gravis due to increased neuromuscular transmission

Q12. Which of the following is a contraindication or caution for edrophonium use?

• History of severe bradyarrhythmia
• Hyperthyroidism with no cardiovascular issues
• Mild seasonal allergies
• Recent minor skin abrasion

Correct Answer: History of severe bradyarrhythmia

Q13. Edrophonium’s main route of elimination is:

• Hepatic metabolism by CYP450 enzymes
• Renal excretion of unchanged drug
• Exhalation via lungs
• Biliary excretion as glucuronide

Correct Answer: Renal excretion of unchanged drug

Q14. Which statement about edrophonium and neuromuscular blocking agents is true?

• Edrophonium potentiates depolarizing blockers like succinylcholine
• Edrophonium reverses non-depolarizing neuromuscular blockade
• Edrophonium produces a permanent block of neuromuscular transmission
• Edrophonium has no interaction with neuromuscular blockers

Correct Answer: Edrophonium reverses non-depolarizing neuromuscular blockade

Q15. Which laboratory parameter is directly affected by edrophonium administration?

• Plasma glucose levels
• Serum creatinine concentration
• Acetylcholinesterase activity
• Hemoglobin concentration

Correct Answer: Acetylcholinesterase activity

Q16. Which clinical sign indicates cholinergic excess after edrophonium?

• Dry mouth and mydriasis
• Diarrhea, salivation, miosis
• Hyperreflexia without secretions
• Loss of tendon reflexes only

Correct Answer: Diarrhea, salivation, miosis

Q17. Edrophonium differs from physostigmine because edrophonium:

• Crosses the blood–brain barrier more readily
• Is quaternary and does not readily enter CNS
• Forms a covalent carbamylated intermediate
• Has longer duration of action in CNS

Correct Answer: Is quaternary and does not readily enter CNS

Q18. The molecular action of edrophonium at the neuromuscular junction increases which neurotransmitter level?

• Norepinephrine
• Adenosine
• Acetylcholine
• GABA

Correct Answer: Acetylcholine

Q19. Which monitoring is most important during an edrophonium test?

• Serum electrolytes every minute
• Continuous cardiac monitoring and observation of muscle strength
• Hourly blood glucose
• Pulse oximetry only in children

Correct Answer: Continuous cardiac monitoring and observation of muscle strength

Q20. Edrophonium is classified pharmacologically as a:

• Muscarinic agonist
• Acetylcholinesterase inhibitor
• Benzodiazepine receptor agonist
• Beta-2 agonist

Correct Answer: Acetylcholinesterase inhibitor

Q21. In which scenario would edrophonium NOT be useful diagnostically?

• Suspected ocular myasthenia gravis
• Differentiating presynaptic Lambert–Eaton syndrome
• Confirming response in generalized myasthenia gravis
• Checking transient improvement in bulbar weakness

Correct Answer: Differentiating presynaptic Lambert–Eaton syndrome

Q22. Which receptor type at the neuromuscular junction is indirectly affected by edrophonium?

• Muscarinic M2 receptors on heart only
• Nicotinic acetylcholine receptors on the motor endplate
• GABA-A receptors in CNS
• Dopamine D2 receptors

Correct Answer: Nicotinic acetylcholine receptors on the motor endplate

Q23. Why must atropine be available when administering edrophonium?

• To reverse excessive cholinergic muscarinic effects like bradycardia
• To enhance edrophonium action on nicotinic receptors
• Atropine potentiates edrophonium’s AChE inhibition
• No need for atropine; it antagonizes edrophonium’s effect

Correct Answer: To reverse excessive cholinergic muscarinic effects like bradycardia

Q24. Which pharmacokinetic property explains edrophonium’s short duration?

• Strong covalent binding to AChE
• Rapid renal elimination and noncovalent binding
• Extensive hepatic metabolism producing active metabolites
• Depot storage in adipose tissue

Correct Answer: Rapid renal elimination and noncovalent binding

Q25. Edrophonium’s reversible inhibition is primarily due to:

• Hydrophobic integration into membrane lipids
• Electrostatic interactions with the enzyme anionic site
• Covalent attachment to serine OH
• Irreversible inactivation by phosphorylation

Correct Answer: Electrostatic interactions with the enzyme anionic site

Q26. In a patient receiving edrophonium, which sign suggests a myasthenic response rather than cholinergic crisis?

• Worsening weakness after injection
• No change in muscle strength
• Transient improvement in muscle strength
• Profuse sweating and increased salivation without strength change

Correct Answer: Transient improvement in muscle strength

Q27. Which drug interaction is most relevant with edrophonium?

• Concurrent beta-blockers eliminating all side effects
• Potentiation of muscarinic effects when combined with cholinomimetics
• Complete antagonism by H2 antagonists
• No interactions with anesthetic agents

Correct Answer: Potentiation of muscarinic effects when combined with cholinomimetics

Q28. Which measurement declines following edrophonium administration in an enzymatic assay?

• Plasma acetylcholinesterase activity
• Blood urea nitrogen
• Serum albumin
• Platelet count

Correct Answer: Plasma acetylcholinesterase activity

Q29. Edrophonium would be least appropriate for which therapeutic purpose?

• Short-term reversal of non-depolarizing blockade in anesthesia
• Diagnostic Tensilon test for suspected myasthenia gravis
• Long-term maintenance therapy for myasthenia gravis
• Clinical differentiation of neuromuscular weakness causes

Correct Answer: Long-term maintenance therapy for myasthenia gravis

Q30. The typical adult intravenous dose range of edrophonium for Tensilon test (conceptually) is:

• Large single dose of 2 grams IV
• Incremental small doses totaling a few milligrams
• Continuous infusion for 24 hours
• Topical ocular drops only

Correct Answer: Incremental small doses totaling a few milligrams

Q31. Which of the following best explains why edrophonium rarely causes central nervous system effects?

• It is highly lipophilic and sequestered peripherally
• It is a quaternary ammonium compound with poor BBB penetration
• It is actively pumped out of the brain by P-glycoprotein only
• It is converted to an inactive metabolite before reaching CNS

Correct Answer: It is a quaternary ammonium compound with poor BBB penetration

Q32. Which clinical test result after edrophonium would indicate a cholinergic crisis?

• Improvement in muscle strength and decreased ptosis
• Marked worsening of muscle weakness and fasciculations
• No change in secretions or heart rate
• Immediate onset of hypertension only

Correct Answer: Marked worsening of muscle weakness and fasciculations

Q33. Which enzyme types does edrophonium inhibit?

• Acetylcholinesterase primarily, with minor effects on butyrylcholinesterase
• CYP450 isozymes selectively
• Monoamine oxidase (MAO)
• Proteases in plasma

Correct Answer: Acetylcholinesterase primarily, with minor effects on butyrylcholinesterase

Q34. Which adverse cardiac effect is a concern with edrophonium?

• Sinus tachycardia only
• Bradyarrhythmias and possible asystole
• Isolated hypertension without bradycardia
• Cardiomyopathy with long-term use

Correct Answer: Bradyarrhythmias and possible asystole

Q35. Edrophonium’s clinical usefulness in myasthenia gravis is due to its ability to:

• Increase ACh degradation at synapse
• Increase acetylcholine availability at neuromuscular junction
• Block nicotinic receptors permanently
• Inhibit acetylcholine synthesis

Correct Answer: Increase acetylcholine availability at neuromuscular junction

Q36. Which pharmacological property distinguishes edrophonium from organophosphates?

• Both cause irreversible AChE inhibition
• Edrophonium causes reversible noncovalent inhibition; organophosphates cause irreversible phosphorylation
• Edrophonium phosphorylates AChE permanently
• Organophosphates are short-acting like edrophonium

Correct Answer: Edrophonium causes reversible noncovalent inhibition; organophosphates cause irreversible phosphorylation

Q37. Which clinical symptom would you monitor closely after edrophonium administration in an elderly patient?

• Increased appetite and weight gain
• Excessive bronchial secretions and bradycardia
• Gradual hair loss
• Improved hearing acuity

Correct Answer: Excessive bronchial secretions and bradycardia

Q38. How does edrophonium affect gastrointestinal motility?

• It decreases GI motility leading to constipation
• It increases GI motility and secretions
• No effect on GI tract whatsoever
• It selectively blocks gastric acid secretion

Correct Answer: It increases GI motility and secretions

Q39. In pharmacology exams, edrophonium is often grouped with:

• Beta-lactam antibiotics
• Reversible acetylcholinesterase inhibitors
• Calcium channel blockers
• Opioid analgesics

Correct Answer: Reversible acetylcholinesterase inhibitors

Q40. Which is a major difference between edrophonium and pyridostigmine?

• Both have identical duration and oral bioavailability
• Pyridostigmine is suitable for oral long-term therapy; edrophonium is short-acting and mainly IV
• Edrophonium is used chronically; pyridostigmine is only diagnostic
• Pyridostigmine is quaternary and cannot be given orally

Correct Answer: Pyridostigmine is suitable for oral long-term therapy; edrophonium is short-acting and mainly IV

Q41. Which clinical condition could produce a false-positive Tensilon test?

• Pure psychological weakness without neuromuscular pathology
• Lambert–Eaton syndrome showing transient improvement
• Primary muscle disease with no cholinesterase involvement
• Congenital myopathy that responds the same way

Correct Answer: Lambert–Eaton syndrome showing transient improvement

Q42. Which monitoring parameter helps differentiate myasthenic from cholinergic crisis after edrophonium?

• Change in white blood cell count
• Change in muscle strength and respiratory function
• Blood glucose variability
• Serum potassium drop

Correct Answer: Change in muscle strength and respiratory function

Q43. Which statement about edrophonium and butyrylcholinesterase is correct?

• Edrophonium selectively inhibits only butyrylcholinesterase
• Edrophonium primarily inhibits acetylcholinesterase but may affect butyrylcholinesterase to a lesser degree
• Edrophonium activates butyrylcholinesterase
• Edrophonium is metabolized exclusively by butyrylcholinesterase

Correct Answer: Edrophonium primarily inhibits acetylcholinesterase but may affect butyrylcholinesterase to a lesser degree

Q44. Which patient would require special caution when using edrophonium?

• Patient on anticholinergic therapy only
• Patient with asthma and bronchospasm risk due to increased secretions
• Patient with uncomplicated controlled hypertension
• Patient with seasonal allergic rhinitis

Correct Answer: Patient with asthma and bronchospasm risk due to increased secretions

Q45. Edrophonium’s effect on sweat glands is to:

• Decrease sweating via sympathetic blockade
• Increase sweating due to muscarinic stimulation
• No change since sweat glands are adrenergic
• Cause anhidrosis selectively on palms

Correct Answer: Increase sweating due to muscarinic stimulation

Q46. Which laboratory assay might use edrophonium in a research setting?

• Assay to measure cholinesterase activity in plasma
• Serum amylase activity assay unrelated to cholinesterase
• HbA1c measurement for diabetes
• Liver function test panel

Correct Answer: Assay to measure cholinesterase activity in plasma

Q47. Which of the following best describes edrophonium’s chemical class?

• Organophosphate
• Carbamate ester
• Quaternary ammonium alcohol
• Benzodiazepine derivative

Correct Answer: Quaternary ammonium alcohol

Q48. When counselling a patient undergoing diagnostic testing with edrophonium, which point is important?

• No side effects are possible and no monitoring is needed
• Effects are transient; brief improvement or worsening may occur and monitoring will be provided
• They must drive immediately after the test
• They should stop all cardiac medications before the test

Correct Answer: Effects are transient; brief improvement or worsening may occur and monitoring will be provided

Q49. Which of the following best justifies edrophonium’s limited therapeutic use?

• Its rapid onset and very long duration make dosing difficult
• Short duration and need for intravenous administration limit chronic use
• High oral bioavailability and prolonged CNS effects
• It causes irreversible changes in acetylcholinesterase

Correct Answer: Short duration and need for intravenous administration limit chronic use

Q50. For exam-focused pharmacology, understanding edrophonium helps primarily to:

• Illustrate principles of irreversible enzyme inhibition only
• Demonstrate short-acting reversible AChE inhibition, clinical testing, and side-effect management
• Teach antibiotic stewardship
• Show typical pharmacology of corticosteroids

Correct Answer: Demonstrate short-acting reversible AChE inhibition, clinical testing, and side-effect management

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.

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