Direct acting parasympathomimetics – Bethanechol MCQs With Answer

Direct acting parasympathomimetics – Bethanechol MCQs With Answer
Direct acting parasympathomimetics, especially bethanechol, are essential topics in pharmacology for B.Pharm students. This introduction covers pharmacodynamics, receptor selectivity, clinical uses (postoperative ileus, non‑obstructive urinary retention), pharmacokinetics (quaternary ammonium, poor CNS penetration, resistance to acetylcholinesterase), adverse effects, contraindications and antidotes. Understanding bethanechol’s mechanism as a selective muscarinic agonist (M3 predominance), dosing routes, drug interactions and monitoring is critical for safe therapeutic use and exam preparation. These focused, keyword‑rich points will help you master direct parasympathomimetics and related exam concepts. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which receptor subtype primarily mediates bethanechol’s contractile effect on the urinary bladder detrusor muscle?

• M1 muscarinic receptor
• M2 muscarinic receptor
• M3 muscarinic receptor
• Nicotinic receptor

Correct Answer: M3 muscarinic receptor

Q2. Bethanechol is classified as a direct-acting parasympathomimetic because it:

• Inhibits acetylcholinesterase activity
• Directly stimulates muscarinic receptors
• Blocks muscarinic receptors
• Enhances norepinephrine release

Correct Answer: Directly stimulates muscarinic receptors

Q3. Which chemical property of bethanechol limits its ability to cross the blood-brain barrier?

Hydrophobic aromatic ring
• Quaternary ammonium group
• High lipid solubility
• Neutral pKa near physiological pH

Correct Answer: Quaternary ammonium group

Q4. Compared to acetylcholine, bethanechol is more resistant to hydrolysis by acetylcholinesterase because it is:

• An alkaloid tertiary amine
• A choline ester with a beta‑methyl group
• A catecholamine derivative
• A long‑chain fatty ester

Correct Answer: A choline ester with a beta‑methyl group

Q5. Primary therapeutic indications for bethanechol include:

• Hypertension and angina
• Non-obstructive urinary retention and postoperative ileus
• Asthma and COPD maintenance
• Parkinson’s disease motor symptoms

Correct Answer: Non-obstructive urinary retention and postoperative ileus

Q6. Which route of administration is commonly used for bethanechol to treat urinary retention?

• Intravenous infusion
• Subcutaneous or oral administration
• Inhalation aerosol
• Intrathecal injection

Correct Answer: Subcutaneous or oral administration

Q7. Which of the following adverse effects is most characteristic of bethanechol therapy?

• Tachycardia and dry mouth
• Bronchodilation and tremor
• Bradycardia, sweating, salivation, and diarrhea
• Hyperglycemia and polyuria

Correct Answer: Bradycardia, sweating, salivation, and diarrhea

Q8. Which drug is the first-line antidote for bethanechol overdose causing severe muscarinic effects?

• Atropine
• Propranolol
• Neostigmine
• Physostigmine

Correct Answer: Atropine

Q9. Which statement about bethanechol and cholinesterase inhibitors is correct?

• They have antagonistic effects on muscarinic receptors
• They produce additive cholinergic effects
• Cholinesterase inhibitors inactivate bethanechol
• They produce only nicotinic effects together

Correct Answer: They produce additive cholinergic effects

Q10. Why is bethanechol not useful for treating myasthenia gravis?

• It selectively blocks nicotinic receptors
• It is a muscarinic agonist and does not enhance neuromuscular transmission
• It is rapidly degraded at the neuromuscular junction
• It causes irreversible acetylcholinesterase inhibition

Correct Answer: It is a muscarinic agonist and does not enhance neuromuscular transmission

Q11. Which structural class does bethanechol belong to?

• Tertiary alkaloid (pilocarpine type)
• Choline ester (quaternary ammonium)
• Catecholamine derivative
• Phosphodiesterase inhibitor

Correct Answer: Choline ester (quaternary ammonium)

Q12. Bethanechol’s predominant effect on the gastrointestinal tract is to:

• Decrease gastric secretions and relax smooth muscle
• Increase gastric motility and relax sphincters promoting peristalsis
• Inhibit enteric neurons causing ileus
• Block serotonin receptors in the gut

Correct Answer: Increase gastric motility and relax sphincters promoting peristalsis

Q13. Which patient condition is an absolute contraindication to bethanechol therapy?

• Non-obstructive urinary retention
• Obstructive urinary retention due to prostatic hypertrophy
• Postoperative ileus without obstruction
• Radiation-induced bladder atony

Correct Answer: Obstructive urinary retention due to prostatic hypertrophy

Q14. Which pharmacokinetic property explains bethanechol’s short systemic effects?

• Rapid hepatic metabolism via CYP450 3A4
• Poor oral bioavailability and rapid renal excretion
• High protein binding leading to slow onset
• Strong binding to plasma cholinesterase prolonging action

Correct Answer: Poor oral bioavailability and rapid renal excretion

Q15. Which clinical sign would suggest bethanechol-induced muscarinic overactivity?

• Mydriasis and dry skin
• Miosis, bronchospasm, increased salivation and lacrimation
• Hyperreflexia and muscle rigidity
• Hypoglycemia and sweating only

Correct Answer: Miosis, bronchospasm, increased salivation and lacrimation

Q16. Which receptor subtype is primarily responsible for bronchoconstriction seen with bethanechol?

• M1 receptor
• M2 receptor
• M3 receptor
• Nicotinic receptor

Correct Answer: M3 receptor

Q17. Which of the following best describes bethanechol’s effect on blood pressure?

• Produces sustained hypertension via alpha-agonism
• May produce transient hypotension due to vasodilation mediated by endothelial M3 receptors
• Causes prolonged tachycardia and hypertension
• No cardiovascular effects at therapeutic doses

Correct Answer: May produce transient hypotension due to vasodilation mediated by endothelial M3 receptors

Q18. Which electrolyte or laboratory parameter might be monitored during excessive cholinergic stimulation from bethanechol?

• Serum potassium for hyperkalemia risk
• Serum creatinine for renal function and drug clearance
• Serum calcium for tetany
• Serum amylase for pancreatitis only

Correct Answer: Serum creatinine for renal function and drug clearance

Q19. Which drug interaction increases risk of severe bradycardia when co-administered with bethanechol?

• Beta-adrenergic agonists
• Beta-blockers such as propranolol
• H2 receptor antagonists
• Loop diuretics

Correct Answer: Beta-blockers such as propranolol

Q20. Which muscarinic agonist is structurally more lipophilic and crosses the blood-brain barrier, unlike bethanechol?

• Pilocarpine
• Carbachol
• Edrophonium
• Neostigmine

Correct Answer: Pilocarpine

Q21. What is the primary mechanism of bethanechol’s selectivity for muscarinic over nicotinic receptors?

• Its long alkyl side chain binds nicotinic receptors selectively
• Structural configuration favors binding to muscarinic receptor subtypes
• It is an irreversible inhibitor of nicotinic receptors
• It is converted to acetylcholine in vivo which prefers muscarinic sites

Correct Answer: Structural configuration favors binding to muscarinic receptor subtypes

Q22. In which patient population should bethanechol be used with extreme caution due to risk of bronchospasm?

• Patients with hypertension
• Patients with asthma or chronic obstructive pulmonary disease
• Patients with peptic ulcer disease
• Patients taking ACE inhibitors

Correct Answer: Patients with asthma or chronic obstructive pulmonary disease

Q23. Which clinical scenario best corresponds to an appropriate use of bethanechol?

• Management of acute closed-angle glaucoma
• Treatment of non-obstructive postoperative bladder atony
• Control of severe asthma exacerbation
• Relief of peptic ulcer pain

Correct Answer: Treatment of non-obstructive postoperative bladder atony

Q24. Which patient complaint would most likely indicate an adverse effect of bethanechol?

• Dry mouth and constipation
• Wheezing and shortness of breath
• Insomnia and agitation
• Blurred vision due to mydriasis

Correct Answer: Wheezing and shortness of breath

Q25. Bethanechol’s maximal muscarinic effects are mediated via which intracellular signaling for M3 receptors?

• cAMP increase via Gs protein
• Inhibition of adenylate cyclase via Gi protein
• PLC activation → IP3/DAG → increased intracellular Ca2+
• Direct opening of potassium channels via Gβγ

Correct Answer: PLC activation → IP3/DAG → increased intracellular Ca2+

Q26. Which of the following is NOT a typical sign of muscarinic excess from bethanechol?

• Hypersalivation
• Bronchospasm
• Skeletal muscle fasciculations due to nicotinic stimulation
• Diarrhea and abdominal cramps

Correct Answer: Skeletal muscle fasciculations due to nicotinic stimulation

Q27. Which cholinomimetic drug is preferred for glaucoma because it reduces intraocular pressure by increasing aqueous outflow and crosses the cornea effectively?

• Bethanechol
• Pilocarpine
• Neostigmine
• Atropine

Correct Answer: Pilocarpine

Q28. Which physiological effect would bethanechol have on the gastrointestinal sphincters?

• Contraction of the lower esophageal sphincter and relaxation of the pyloric sphincter
• Relaxation of sphincters promoting gastric emptying and intestinal transit
• Increase in sphincter tone leading to constipation
• No effect on sphincter function

Correct Answer: Relaxation of sphincters promoting gastric emptying and intestinal transit

Q29. Which monitoring parameter is most important when initiating bethanechol in elderly patients?

• Pulse rate and blood pressure
• Serum cholesterol level
• Thyroid function tests
• Serum magnesium

Correct Answer: Pulse rate and blood pressure

Q30. Which of the following best explains why bethanechol has limited use in systemic therapy compared with some other cholinomimetics?

• Excessive nicotinic receptor activation
• Frequent and troublesome muscarinic side effects and poor oral bioavailability
• High central nervous system toxicity
• Strong interaction with insulin causing hypoglycemia

Correct Answer: Frequent and troublesome muscarinic side effects and poor oral bioavailability

Q31. Which clinical test could be used to confirm therapeutic effect of bethanechol on bladder function?

• Post-void residual urine volume measurement
• Serum amylase level
• Pulmonary function test only
• Serum troponin measurement

Correct Answer: Post-void residual urine volume measurement

Q32. Which property distinguishes bethanechol from carbachol?

• Bethanechol has significant nicotinic receptor activity while carbachol is muscarinic selective
• Bethanechol is more selective for muscarinic receptors and less nicotinic activity than carbachol
• Carbachol is a quaternary ammonium while bethanechol is tertiary
• Both drugs are identical in receptor selectivity

Correct Answer: Bethanechol is more selective for muscarinic receptors and less nicotinic activity than carbachol

Q33. Which precaution should be taken before giving bethanechol to a patient with suspected bowel obstruction?

• Administer a higher dose to ensure efficacy
• Avoid administration until mechanical obstruction is excluded
• Co-administer with a beta-blocker to prevent tachycardia
• No precaution is necessary

Correct Answer: Avoid administration until mechanical obstruction is excluded

Q34. Which laboratory abnormality could potentiate muscarinic side effects of bethanechol?

• Hyperkalemia
• Renal impairment causing decreased drug clearance
• Hypocalcemia only
• Low serum albumin increasing free drug

Correct Answer: Renal impairment causing decreased drug clearance

Q35. Which statement about bethanechol and pregnancy is most appropriate for a B.Pharm student to remember?

• It is absolutely safe and recommended in all pregnant patients
• Use only if potential benefit justifies potential risk; consult guidelines
• It is a first-line uterotonic agent in labor
• It causes fetal malformations in all trimesters

Correct Answer: Use only if potential benefit justifies potential risk; consult guidelines

Q36. Which cardiovascular effect might be observed after bethanechol administration due to vagal stimulation?

• Marked tachycardia and arrhythmias
• Bradycardia and possible heart block
• Sustained hypertension and chest pain
• Widened pulse pressure only

Correct Answer: Bradycardia and possible heart block

Q37. Which clinical intervention is appropriate for severe bronchospasm caused by bethanechol overdose?

• Administer naloxone
• Give nebulized β2-agonist and supportive oxygen, plus atropine for muscarinic blockade
• Administer succinylcholine
• Use aspirin and NSAIDs

Correct Answer: Give nebulized β2-agonist and supportive oxygen, plus atropine for muscarinic blockade

Q38. Which pharmacological agent would antagonize the urinary and GI effects of bethanechol?

• Neostigmine
• Atropine
• Physostigmine
• Pilocarpine

Correct Answer: Atropine

Q39. Which dosing consideration is correct for bethanechol in treating bladder atony?

• High single oral dose is preferred to avoid side effects
• Start with lowest effective dose and titrate; monitor vitals
• No titration needed because of wide therapeutic index
• Use intramuscular injection only in all patients

Correct Answer: Start with lowest effective dose and titrate; monitor vitals

Q40. Which enzyme primarily hydrolyzes acetylcholine but has limited effect on bethanechol?

• Monoamine oxidase (MAO)
• Butyrylcholinesterase only
• Acetylcholinesterase (AChE)
• Catechol-O-methyltransferase (COMT)

Correct Answer: Acetylcholinesterase (AChE)

Q41. Which effect helps distinguish a muscarinic agonist like bethanechol from a nicotinic agonist clinically?

• Presence of skeletal muscle weakness and paralysis
• Predominant autonomic signs such as miosis, salivation and bradycardia
• Excessive central stimulation and seizures
• Hypertension and mydriasis

Correct Answer: Predominant autonomic signs such as miosis, salivation and bradycardia

Q42. Which effect on sweat glands would bethanechol produce and why is this clinically relevant?

• Decrease sweating by blocking muscarinic receptors; useful in hyperhidrosis
• Increase sweating (cholinergic) which may cause heat intolerance
• No effect on sweat glands because they are adrenergic
• Increase sweating via nicotinic receptors only

Correct Answer: Increase sweating (cholinergic) which may cause heat intolerance

Q43. When preparing a patient for bethanechol therapy, which history is most important to elicit?

• History of peptic ulcer disease and asthma
• History of migraine headaches only
• History of hyperlipidemia only
• History of seasonal allergies only

Correct Answer: History of peptic ulcer disease and asthma

Q44. Which statement about bethanechol’s molecular charge and distribution is correct?

• It is neutral and distributes widely into adipose tissue
• It is a quaternary cation and remains largely in extracellular fluid
• It is highly lipophilic and accumulates in the brain
• It is anionic and binds tightly to albumin

Correct Answer: It is a quaternary cation and remains largely in extracellular fluid

Q45. Which combination would increase bethanechol’s muscarinic effects dangerously?

• Bethanechol plus antimuscarinic (e.g., atropine)
• Bethanechol plus acetylcholinesterase inhibitor (e.g., neostigmine)
• Bethanechol plus β2 agonist
• Bethanechol plus proton pump inhibitor

Correct Answer: Bethanechol plus acetylcholinesterase inhibitor (e.g., neostigmine)

Q46. Which sign differentiates muscarinic overstimulation from opioid overdose?

• Pinpoint pupils and respiratory depression only
• Bradycardia with profuse salivation and bronchospasm
• Severe miosis without salivation
• Hypotension with dry skin

Correct Answer: Bradycardia with profuse salivation and bronchospasm

Q47. Which property makes bethanechol a poor choice for treating central nervous system conditions?

• Excessive central stimulation
• Poor penetration across the blood-brain barrier due to quaternary ammonium structure
• Rapid conversion to central active metabolites
• Strong binding to CNS muscarinic receptors causing sedation

Correct Answer: Poor penetration across the blood-brain barrier due to quaternary ammonium structure

Q48. Which side effect is least likely with therapeutic doses of bethanechol?

• Excessive lacrimation and salivation
• Urinary urgency and increased voiding
• Profound skeletal muscle paralysis
• Abdominal cramps and diarrhea

Correct Answer: Profound skeletal muscle paralysis

Q49. Which statement about bethanechol’s onset and duration after subcutaneous injection is most accurate?

• Very slow onset (days) with extremely prolonged duration
• Rapid onset (minutes) with relatively short duration (hours)
• Immediate onset and irreversible effect
• No systemic effect when given subcutaneously

Correct Answer: Rapid onset (minutes) with relatively short duration (hours)

Q50. For exam preparation, which concept best links bethanechol’s mechanism to its clinical use?

• Bethanechol blocks adrenergic receptors to reduce sphincter tone
• Bethanechol selectively activates muscarinic receptors to increase smooth muscle tone in bladder and GI, treating atony
• Bethanechol inhibits acetylcholine synthesis leading to reduced motility
• Bethanechol is a diuretic that increases urine output by osmotic action

Correct Answer: Bethanechol selectively activates muscarinic receptors to increase smooth muscle tone in bladder and GI, treating atony

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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