Reversible inhibitors – Pyridostigmine MCQs With Answer

Reversible inhibitors – Pyridostigmine MCQs With Answer

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Reversible inhibitors – Pyridostigmine MCQs With Answer

Pyridostigmine is a clinically important reversible acetylcholinesterase inhibitor used widely in pharmacotherapy and toxicology. This concise introduction covers mechanism of action, pharmacokinetics, clinical uses (especially myasthenia gravis and nerve-agent pretreatment), adverse effects, interactions, and distinctions from edrophonium, neostigmine and organophosphates. B. Pharm students will benefit from focused, keyword-rich content on pyridostigmine’s quaternary ammonium structure, carbamate-type inhibition, peripheral selectivity, and management of cholinergic side effects. Practical knowledge of dosing routes, monitoring, and antidote strategies is emphasized to support exam readiness and safe dispensing.
Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which best describes the primary mechanism of action of pyridostigmine?

  • Non-competitive blockade of nicotinic receptors
  • Reversible inhibition of acetylcholinesterase by carbamylation
  • Irreversible phosphorylation of acetylcholinesterase
  • Direct agonism at muscarinic receptors

Correct Answer: Reversible inhibition of acetylcholinesterase by carbamylation

Q2. Pyridostigmine is classified chemically as which of the following?

  • Tertiary amine
  • Organophosphate
  • Quaternary ammonium carbamate
  • Beta-lactam antibiotic

Correct Answer: Quaternary ammonium carbamate

Q3. Which clinical condition is pyridostigmine most commonly used to manage?

  • Hypertension
  • Myasthenia gravis
  • Type 2 diabetes mellitus
  • Parkinson’s disease

Correct Answer: Myasthenia gravis

Q4. Compared with edrophonium, pyridostigmine has which pharmacological advantage for chronic therapy?

  • Faster onset and shorter duration
  • Longer duration of action suitable for oral maintenance
  • Greater central nervous system penetration
  • Irreversible enzyme inhibition

Correct Answer: Longer duration of action suitable for oral maintenance

Q5. Why does pyridostigmine have limited central nervous system effects?

  • It is rapidly metabolized in the brain
  • It is a quaternary ammonium compound that poorly crosses the blood–brain barrier
  • It selectively binds muscarinic receptors only in the periphery
  • It is neutral and lipophilic

Correct Answer: It is a quaternary ammonium compound that poorly crosses the blood–brain barrier

Q6. Which adverse effect is most likely due to pyridostigmine’s muscarinic stimulation?

  • Constipation
  • Dry mouth
  • Bradycardia with increased bronchial secretions
  • Hyperglycemia

Correct Answer: Bradycardia with increased bronchial secretions

Q7. For suspected pyridostigmine overdose causing excessive muscarinic effects, the immediate antidote is:

  • Pralidoxime (2-PAM)
  • Atropine
  • Physostigmine
  • Naloxone

Correct Answer: Atropine

Q8. Pyridostigmine is often used prophylactically in military settings to protect against which threat?

  • Radiation exposure
  • Nerve agent (organophosphate) poisoning
  • Biological toxins like botulinum
  • Thermal burns

Correct Answer: Nerve agent (organophosphate) poisoning

Q9. Which statement correctly contrasts pyridostigmine and organophosphate inhibitors?

  • Pyridostigmine causes irreversible phosphorylation of AChE
  • Organophosphates cause reversible carbamylation similar to pyridostigmine
  • Pyridostigmine causes reversible carbamylation and has a shorter enzyme-inactivation duration than organophosphates
  • Both have identical clinical management for poisoning

Correct Answer: Pyridostigmine causes reversible carbamylation and has a shorter enzyme-inactivation duration than organophosphates

Q10. Which route(s) of administration are commonly available for pyridostigmine?

  • Topical only
  • Oral and parenteral (IV/IM)
  • Inhalational only
  • Nasal spray only

Correct Answer: Oral and parenteral (IV/IM)

Q11. In myasthenia gravis, pyridostigmine primarily improves muscle strength by:

  • Increasing presynaptic acetylcholine release
  • Blocking acetylcholine receptors
  • Inhibiting acetylcholinesterase to increase synaptic acetylcholine
  • Stimulating muscle protein synthesis

Correct Answer: Inhibiting acetylcholinesterase to increase synaptic acetylcholine

Q12. Which clinical test uses a short-acting acetylcholinesterase inhibitor to differentiate myasthenic from cholinergic crisis?

  • Tensilon (edrophonium) test
  • Electrolyte panel
  • EMG with nerve conduction velocity
  • Serum creatinine measurement

Correct Answer: Tensilon (edrophonium) test

Q13. A key difference between pyridostigmine and edrophonium is:

  • Edrophonium is used for chronic oral therapy
  • Pyridostigmine is longer acting and suitable for maintenance therapy
  • Pyridostigmine is ultrashort acting and used diagnostically
  • Neither affects acetylcholinesterase

Correct Answer: Pyridostigmine is longer acting and suitable for maintenance therapy

Q14. Which cardiovascular effect can occur with therapeutic doses of pyridostigmine?

  • Tachycardia with hypertension
  • Bradycardia and possible heart block
  • Myocardial infarction risk reduction
  • No effect on heart rate

Correct Answer: Bradycardia and possible heart block

Q15. When treating a patient with myasthenia gravis, what is the rationale for individualizing pyridostigmine dosing?

  • Uniform dosing works for all patients
  • Therapeutic window varies; dose titration balances strength improvement versus cholinergic side effects
  • It is only effective at a single high dose
  • Because pyridostigmine has no side effects, dosing is arbitrary

Correct Answer: Therapeutic window varies; dose titration balances strength improvement versus cholinergic side effects

Q16. Which of the following adverse effects is most characteristic of excessive nicotinic stimulation from cholinesterase inhibitors?

  • Bronchoconstriction
  • Muscle fasciculations and weakness
  • Increased salivation only
  • Hyperglycemia

Correct Answer: Muscle fasciculations and weakness

Q17. In the context of anesthesia, pyridostigmine is effective to:

  • Reverse non-depolarizing neuromuscular blockade when combined with an antimuscarinic
  • Potentiate succinylcholine-induced blockade
  • Induce general anesthesia alone
  • Prevent postoperative nausea

Correct Answer: Reverse non-depolarizing neuromuscular blockade when combined with an antimuscarinic

Q18. Which drug would be co-administered to counter muscarinic side effects when reversing neuromuscular blockade with pyridostigmine?

  • Propranolol
  • Atropine or glycopyrrolate
  • Neostigmine
  • Physostigmine

Correct Answer: Atropine or glycopyrrolate

Q19. Which statement about pyridostigmine’s effect on smooth muscle is correct?

  • It relaxes bronchial smooth muscle leading to bronchodilation
  • It enhances gastrointestinal and urinary tract motility via muscarinic stimulation
  • It causes vasodilation by blocking alpha receptors
  • It inhibits bladder contraction leading to urinary retention

Correct Answer: It enhances gastrointestinal and urinary tract motility via muscarinic stimulation

Q20. Which laboratory or clinical sign helps distinguish cholinergic crisis from myasthenic crisis?

  • Improvement with administration of pyridostigmine
  • Both present identically and cannot be distinguished clinically
  • Cholinergic crisis improves with atropine while myasthenic crisis improves with more cholinesterase inhibitor
  • Myasthenic crisis responds to beta-blockers

Correct Answer: Cholinergic crisis improves with atropine while myasthenic crisis improves with more cholinesterase inhibitor

Q21. Which of the following is a typical unwanted peripheral muscarinic effect of pyridostigmine affecting the gut?

  • Constipation
  • Dryness of mouth
  • Abdominal cramps and diarrhea
  • Decreased gastric secretions

Correct Answer: Abdominal cramps and diarrhea

Q22. Which patient condition is a relative contraindication to starting pyridostigmine?

  • Obstructive ileus or mechanical intestinal obstruction
  • Mild fatigue without weakness
  • Well-controlled hypothyroidism
  • Uncomplicated eczema

Correct Answer: Obstructive ileus or mechanical intestinal obstruction

Q23. The pharmacologic classification “carbamate inhibitor” implies which enzymatic interaction?

  • Permanent phosphorylation of acetylcholinesterase
  • Non-covalent reversible binding only
  • Carbamylation of the enzyme active site leading to reversible inhibition
  • Activation of acetylcholinesterase activity

Correct Answer: Carbamylation of the enzyme active site leading to reversible inhibition

Q24. Which statement about pyridostigmine’s onset and duration compared with edrophonium is correct?

  • Pyridostigmine works faster and for a shorter time than edrophonium
  • Pyridostigmine has slower onset but longer duration than edrophonium
  • Both have identical onset and duration
  • Edrophonium has longer duration than pyridostigmine

Correct Answer: Pyridostigmine has slower onset but longer duration than edrophonium

Q25. Which of the following best describes why pralidoxime (2-PAM) is not routinely required for pyridostigmine poisoning?

  • Pyridostigmine does not inhibit acetylcholinesterase
  • Pyridostigmine irreversibly phosphorylates AChE so 2-PAM is ineffective
  • Carbamate-inhibited AChE spontaneously regenerates and pralidoxime is usually unnecessary
  • Pralidoxime exacerbates pyridostigmine toxicity

Correct Answer: Carbamate-inhibited AChE spontaneously regenerates and pralidoxime is usually unnecessary

Q26. Which neuromuscular disorder typically shows limited response to pyridostigmine?

  • Myasthenia gravis
  • Lambert–Eaton myasthenic syndrome (LEMS)
  • Congenital myasthenic syndromes responsive to AChE inhibitors
  • Transient neonatal myasthenia gravis

Correct Answer: Lambert–Eaton myasthenic syndrome (LEMS)

Q27. The brand name or common salt form of pyridostigmine used therapeutically is usually:

  • Pyridostigmine nitrate
  • Pyridostigmine bromide
  • Pyridostigmine chloride
  • Pyridostigmine sulfate

Correct Answer: Pyridostigmine bromide

Q28. Which pharmacokinetic property is true for pyridostigmine after oral administration?

  • Extensive central nervous system accumulation
  • Poor oral bioavailability and no clinical effect
  • Sufficient oral bioavailability for therapeutic maintenance doses
  • Eliminated unchanged exclusively via lungs

Correct Answer: Sufficient oral bioavailability for therapeutic maintenance doses

Q29. Which electrolyte/physiologic monitoring is most relevant when a patient is on high doses of pyridostigmine?

  • Serum sodium for hyponatremia
  • Monitoring for signs of cholinergic excess: bradycardia, bronchospasm, diarrhea
  • Fasting blood glucose for hyperglycemia
  • Serum creatinine for nephrotoxicity

Correct Answer: Monitoring for signs of cholinergic excess: bradycardia, bronchospasm, diarrhea

Q30. Combined use of pyridostigmine with which drug class may worsen bronchospasm in susceptible patients?

  • Beta-2 agonists
  • Antihistamines
  • NSAIDs
  • Cholinesterase inhibitors can worsen bronchospasm in asthma, interacting adversely with beta-blockers

Correct Answer: Cholinesterase inhibitors can worsen bronchospasm in asthma, interacting adversely with beta-blockers

Q31. Which clinical sign would suggest effective therapeutic response to pyridostigmine in myasthenia gravis?

  • Worsening ptosis and fatigability
  • Improved muscle strength and reduced fatigability
  • Development of severe diarrhea only
  • No change in electromyography findings

Correct Answer: Improved muscle strength and reduced fatigability

Q32. How does pyridostigmine influence ocular symptoms in myasthenia gravis?

  • It typically worsens diplopia and ptosis
  • It can transiently improve ptosis and extraocular muscle weakness
  • It cures ocular myasthenia permanently
  • It has no effect on ocular muscles

Correct Answer: It can transiently improve ptosis and extraocular muscle weakness

Q33. Which statement about the duration of enzyme inhibition by pyridostigmine is accurate?

  • It causes permanent enzyme inactivation
  • It produces a transient carbamylated enzyme that regenerates over hours
  • It inhibits AChE for weeks
  • It does not interact with enzyme active site

Correct Answer: It produces a transient carbamylated enzyme that regenerates over hours

Q34. A drug interaction that can enhance pyridostigmine toxicity is co-administration with:

  • Anticholinergics like atropine
  • Beta-agonists
  • Potentiating cholinergic drugs such as other acetylcholinesterase inhibitors
  • High-dose vitamin C

Correct Answer: Potentiating cholinergic drugs such as other acetylcholinesterase inhibitors

Q35. Which sign is more characteristic of cholinergic crisis than myasthenic crisis?

  • Improved strength after edrophonium
  • Excessive salivation, lacrimation, miosis, bronchospasm
  • Pure motor weakness with minimal secretions
  • Hypertension and tachycardia

Correct Answer: Excessive salivation, lacrimation, miosis, bronchospasm

Q36. In which scenario is edrophonium preferred over pyridostigmine?

  • Long-term maintenance therapy for myasthenia gravis
  • Rapid diagnostic testing (Tensilon test) due to short action
  • Prophylaxis against nerve agents
  • Chronic gastrointestinal hypomotility

Correct Answer: Rapid diagnostic testing (Tensilon test) due to short action

Q37. Which of the following is a potential respiratory complication of pyridostigmine overdose?

  • Respiratory muscle weakness and bronchospasm leading to respiratory failure
  • Pulmonary embolism
  • Pneumothorax
  • Primary pulmonary hypertension

Correct Answer: Respiratory muscle weakness and bronchospasm leading to respiratory failure

Q38. Which monitoring is important when starting pyridostigmine in an elderly patient?

  • Only renal ultrasound
  • Monitoring for bradycardia, increased secretions, urinary frequency and falls due to weakness
  • Daily MRI scans
  • Continuous glucose monitoring for hypoglycemia

Correct Answer: Monitoring for bradycardia, increased secretions, urinary frequency and falls due to weakness

Q39. Which statement about pyridostigmine and pregnancy/breastfeeding counseling is most appropriate for pharmacy students?

  • Pyridostigmine is absolutely contraindicated in pregnancy
  • Benefits and risks should be discussed; pyridostigmine is used in pregnancy when benefits outweigh risks
  • Pyridostigmine is a sedative and requires no counseling
  • Pyridostigmine always requires cessation of breastfeeding

Correct Answer: Benefits and risks should be discussed; pyridostigmine is used in pregnancy when benefits outweigh risks

Q40. Which pharmacologic property explains why pyridostigmine is effective at the neuromuscular junction?

  • High affinity for central muscarinic receptors
  • Inhibition of acetylcholinesterase at peripheral synapses increases ACh concentration at motor end-plates
  • Blockade of voltage-gated sodium channels at muscle
  • Activation of catecholamine release from adrenal medulla

Correct Answer: Inhibition of acetylcholinesterase at peripheral synapses increases ACh concentration at motor end-plates

Q41. Which adverse drug reaction should pharmacists counsel patients to expect when initiating pyridostigmine?

  • Improved appetite with weight gain only
  • Gastrointestinal cramps, diarrhea, increased salivation, sweating
  • Sudden blindness
  • Hyperactivity and insomnia

Correct Answer: Gastrointestinal cramps, diarrhea, increased salivation, sweating

Q42. Pyridostigmine differs from physostigmine in that:

  • Physostigmine is a quaternary ammonium compound with poor CNS penetration
  • Pyridostigmine crosses the blood–brain barrier readily
  • Physostigmine is tertiary and can enter the CNS; pyridostigmine does not readily cross into CNS
  • Both have identical CNS penetration

Correct Answer: Physostigmine is tertiary and can enter the CNS; pyridostigmine does not readily cross into CNS

Q43. Which clinical scenario would most likely require withholding pyridostigmine?

  • Mild ocular weakness
  • Acute mechanical intestinal obstruction
  • Stable myasthenia control on current dose
  • After successful thymectomy and symptom-free period

Correct Answer: Acute mechanical intestinal obstruction

Q44. Which effect on pupils would you expect with pyridostigmine therapy or overdose?

  • Mydriasis (dilated pupils)
  • Miosis (constricted pupils)
  • No change in pupil size
  • Pupillary atrophy

Correct Answer: Miosis (constricted pupils)

Q45. Pyridostigmine’s role in nerve-agent pretreatment is best described as:

  • A permanent protective covalent modifier of AChE
  • A reversible protector that occupies AChE to reduce irreversible organophosphate binding
  • An antidote that reverses organophosphate poisoning after exposure
  • A sedative agent to calm soldiers

Correct Answer: A reversible protector that occupies AChE to reduce irreversible organophosphate binding

Q46. During counseling, which advice about timing of pyridostigmine relative to meals is appropriate?

  • Take always with a large fatty meal to enhance central effects
  • Dosing may be timed around meals since gastrointestinal side effects can occur; some patients take after meals to reduce cramps
  • Must be taken strictly on an empty stomach only
  • Take it only at bedtime

Correct Answer: Dosing may be timed around meals since gastrointestinal side effects can occur; some patients take after meals to reduce cramps

Q47. What is the main pharmacodynamic distinction between reversible carbamate inhibitors like pyridostigmine and irreversible organophosphates?

  • Carbamates produce permanent enzyme inactivation while organophosphates are reversible
  • Carbamates form a carbamylated enzyme that spontaneously regenerates; organophosphates phosphorylate AChE often irreversibly after aging
  • Both act as direct cholinergic receptor agonists
  • Neither interacts with acetylcholinesterase

Correct Answer: Carbamates form a carbamylated enzyme that spontaneously regenerates; organophosphates phosphorylate AChE often irreversibly after aging

Q48. Which monitoring is least relevant for a patient stabilized on pyridostigmine?

  • Assessment of muscle strength and functional capacity
  • Monitoring for cholinergic adverse effects and heart rate
  • Serial measurement of serum acetylcholinesterase activity for routine dose adjustment
  • Patient-reported symptoms like dysphagia or dyspnea

Correct Answer: Serial measurement of serum acetylcholinesterase activity for routine dose adjustment

Q49. A pharmacist should warn a patient that combining pyridostigmine with which drug may reduce its efficacy by blocking cholinergic receptors?

  • Atropine (antimuscarinic)
  • Neostigmine (another AChE inhibitor)
  • Organophosphates
  • Bethanechol (muscarinic agonist)

Correct Answer: Atropine (antimuscarinic)

Q50. Which educational point is essential for patients self-administering pyridostigmine for myasthenia gravis?

  • Stop the drug immediately if any muscle strength improves
  • Be aware of signs of cholinergic excess and seek help if severe weakness, breathing difficulty, excessive secretions or severe diarrhea occur
  • Double the dose if missed one
  • It provides immediate and permanent cure

Correct Answer: Be aware of signs of cholinergic excess and seek help if severe weakness, breathing difficulty, excessive secretions or severe diarrhea occur

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