Alpha adrenergic blockers – Phenoxybenzamine MCQs With Answer

Alpha adrenergic blockers – Phenoxybenzamine MCQs With Answer

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Alpha adrenergic blockers – Phenoxybenzamine MCQs With Answer

Phenoxybenzamine is a classic irreversible, non-selective alpha adrenergic blocker widely discussed in B.Pharm pharmacology. This alkylating agent covalently inactivates alpha-1 and alpha-2 receptors, producing prolonged vasodilation and unique pharmacodynamic effects such as epinephrine reversal and reflex tachycardia. Understanding its mechanism, receptor selectivity, clinical use in pheochromocytoma, preoperative management, adverse effects, and pharmacokinetics is essential for pharmacy students. These MCQs focus on mechanism of action, comparisons with selective alpha blockers, therapeutic considerations, side effects, and drug interactions to deepen your grasp of alpha blockers and safe patient care. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which statement best describes the mechanism of action of phenoxybenzamine?

  • Reversible competitive blockade of alpha-1 receptors only
  • Irreversible covalent blockade of alpha-1 and alpha-2 receptors
  • Selective beta-1 adrenergic antagonism
  • Monoamine oxidase inhibition

Correct Answer: Irreversible covalent blockade of alpha-1 and alpha-2 receptors

Q2. Phenoxybenzamine is most appropriately classified as which type of drug?

  • Selective alpha-1 blocker
  • Non-selective irreversible alpha blocker
  • Reversible non-selective alpha blocker
  • Selective beta-2 agonist

Correct Answer: Non-selective irreversible alpha blocker

Q3. Which clinical indication is phenoxybenzamine most commonly associated with?

  • Chronic stable angina
  • Pheochromocytoma preoperative blood pressure control
  • Essential hypertension first-line therapy
  • Acute anaphylaxis

Correct Answer: Pheochromocytoma preoperative blood pressure control

Q4. The “epinephrine reversal” phenomenon after phenoxybenzamine administration is due to:

  • Blocked beta receptors causing unopposed alpha vasoconstriction
  • Blocked alpha receptors leaving beta-2 vasodilation unopposed
  • Inhibition of epinephrine synthesis
  • Increased baroreceptor sensitivity

Correct Answer: Blocked alpha receptors leaving beta-2 vasodilation unopposed

Q5. Which of the following adverse effects is most commonly seen with phenoxybenzamine?

  • Bradycardia without orthostatic symptoms
  • Orthostatic hypotension and nasal congestion
  • Severe bronchospasm
  • Hyperkalemia

Correct Answer: Orthostatic hypotension and nasal congestion

Q6. Phenoxybenzamine’s blockade of presynaptic alpha-2 receptors leads to which effect on norepinephrine release?

  • Decrease in norepinephrine release
  • No change in norepinephrine release
  • Increase in norepinephrine release
  • Complete cessation of norepinephrine synthesis

Correct Answer: Increase in norepinephrine release

Q7. Compared with phentolamine, phenoxybenzamine differs primarily by being:

  • More selective for alpha-1 receptors
  • Irreversible while phentolamine is reversible
  • A beta-blocker rather than an alpha-blocker
  • Shorter acting than phentolamine

Correct Answer: Irreversible while phentolamine is reversible

Q8. Which G-protein is coupled to alpha-1 adrenergic receptors and mediates vasoconstriction?

  • Gs
  • Gi
  • Gq
  • Gt

Correct Answer: Gq

Q9. Alpha-2 adrenergic receptors primarily signal via which G-protein to inhibit adenylyl cyclase?

  • Gs
  • Gi
  • Gq
  • Go

Correct Answer: Gi

Q10. In preoperative management of pheochromocytoma, the correct sequence to avoid hypertensive crises is:

  • Beta-blocker first, then alpha-blocker
  • Alpha-blocker first, then beta-blocker if needed
  • Calcium channel blocker only
  • No antihypertensive therapy before surgery

Correct Answer: Alpha-blocker first, then beta-blocker if needed

Q11. Which of the following best explains reflex tachycardia observed with phenoxybenzamine?

  • Direct beta-1 agonism by phenoxybenzamine
  • Baroreceptor-mediated sympathetic activation due to vasodilation
  • Central vagal stimulation
  • Enhanced acetylcholine release at the SA node

Correct Answer: Baroreceptor-mediated sympathetic activation due to vasodilation

Q12. Phenoxybenzamine’s irreversible action at alpha receptors means recovery of function requires:

  • Administration of a competitive antagonist
  • Metabolic inactivation of the drug
  • Synthesis of new receptor proteins
  • Dialysis to remove the drug

Correct Answer: Synthesis of new receptor proteins

Q13. Which chemical class does phenoxybenzamine belong to?

  • Beta-lactam
  • Haloalkylamine (alkylating agent)
  • Benzodiazepine
  • Calcium channel blocker

Correct Answer: Haloalkylamine (alkylating agent)

Q14. Which laboratory or clinical effect would support adequate alpha blockade by phenoxybenzamine before pheochromocytoma surgery?

  • Persistent severe hypertension despite therapy
  • Orthostatic hypotension on standing
  • Marked bradycardia while supine
  • Unchanged plasma catecholamine levels

Correct Answer: Orthostatic hypotension on standing

Q15. The primary therapeutic rationale for using phenoxybenzamine in pheochromocytoma is to:

  • Stimulate catecholamine secretion to localize the tumor
  • Prevent catecholamine-induced vasoconstriction during tumor manipulation
  • Increase tumor sensitivity to chemotherapy
  • Reduce catecholamine synthesis in the adrenal medulla

Correct Answer: Prevent catecholamine-induced vasoconstriction during tumor manipulation

Q16. Which of the following is NOT a common side effect of phenoxybenzamine?

  • Nasal congestion
  • Orthostatic hypotension
  • Impotence or impaired ejaculation
  • Excessive bradycardia without hypotension

Correct Answer: Excessive bradycardia without hypotension

Q17. Regarding receptor selectivity, phenoxybenzamine blocks:

  • Only alpha-1 receptors
  • Only alpha-2 receptors
  • Both alpha-1 and alpha-2 receptors non-selectively
  • Only beta receptors

Correct Answer: Both alpha-1 and alpha-2 receptors non-selectively

Q18. Why should beta-blockers be started only after adequate alpha blockade in pheochromocytoma?

  • Beta-blockers potentiate alpha receptor activity
  • Beta-blockers alone increase alpha-mediated vasoconstriction leading to hypertensive crisis
  • Beta-blockers increase catecholamine production
  • Beta-blockers cause irreversible alpha blockade

Correct Answer: Beta-blockers alone increase alpha-mediated vasoconstriction leading to hypertensive crisis

Q19. Which pharmacokinetic property explains the prolonged clinical effect of phenoxybenzamine?

  • Rapid renal excretion without metabolism
  • Covalent irreversible binding to receptors independent of plasma half-life
  • High first-pass hepatic activation
  • Short plasma half-life requiring continuous infusion

Correct Answer: Covalent irreversible binding to receptors independent of plasma half-life

Q20. If a patient on phenoxybenzamine receives epinephrine, what is the expected hemodynamic response?

  • Augmented hypertensive response due to alpha sensitization
  • Paradoxical decrease in blood pressure (epinephrine reversal)
  • No change in blood pressure
  • Severe bradycardia due to unopposed vagal tone

Correct Answer: Paradoxical decrease in blood pressure (epinephrine reversal)

Q21. Which other drug is a reversible non-selective alpha antagonist often compared with phenoxybenzamine?

  • Prazosin
  • Propranolol
  • Phentolamine
  • Tamsulosin

Correct Answer: Phentolamine

Q22. A major difference in clinical use between phenoxybenzamine and prazosin is:

  • Prazosin is irreversible while phenoxybenzamine is reversible
  • Phenoxybenzamine is non-selective while prazosin is selective for alpha-1
  • Both drugs are identical in receptor selectivity
  • Prazosin is primarily a beta-blocker

Correct Answer: Phenoxybenzamine is non-selective while prazosin is selective for alpha-1

Q23. Which adverse effect relates specifically to alpha-2 blockade by phenoxybenzamine?

  • Decreased norepinephrine release producing bradycardia
  • Increased norepinephrine release leading to tachycardia
  • Bronchoconstriction via muscarinic receptors
  • Renal sodium retention causing hypertension

Correct Answer: Increased norepinephrine release leading to tachycardia

Q24. Which clinical scenario would be a relative contraindication or caution for phenoxybenzamine therapy?

  • Patients with severe orthostatic hypotension
  • Patients with uncontrolled hypertension from pheochromocytoma
  • Patients needing preoperative alpha blockade
  • Patients with acute hypertensive emergency due to pheochromocytoma

Correct Answer: Patients with severe orthostatic hypotension

Q25. Phenoxybenzamine’s effect on pupillary size is due to blockade of which receptor action?

  • Beta-2 mediated pupillary constriction
  • Alpha-1 mediated pupillary dilation (mydriasis) blockade leading to miosis
  • Muscarinic receptor stimulation causing mydriasis
  • Direct optic nerve effects

Correct Answer: Alpha-1 mediated pupillary dilation (mydriasis) blockade leading to miosis

Q26. When comparing onset and duration, phenoxybenzamine is characterized by:

  • Rapid onset and very short duration
  • Slow onset and long duration due to irreversible binding
  • Immediate reversal with naloxone
  • Duration equivalent to plasma half-life only

Correct Answer: Slow onset and long duration due to irreversible binding

Q27. Which monitoring parameter is most important during phenoxybenzamine initiation?

  • Serum potassium levels only
  • Blood pressure in supine and standing positions
  • Liver enzymes weekly
  • Pulmonary function tests

Correct Answer: Blood pressure in supine and standing positions

Q28. Which drug interaction is clinically relevant with phenoxybenzamine?

  • Concurrent use with MAO inhibitors reduces hypotensive effects
  • Co-administration with sympathomimetics may have unpredictable effects due to receptor blockade
  • Phenoxybenzamine enhances platelet aggregation with aspirin
  • No significant interactions are known

Correct Answer: Co-administration with sympathomimetics may have unpredictable effects due to receptor blockade

Q29. Which statement about reversing phenoxybenzamine’s pharmacologic effects in an emergency is correct?

  • Administering a competitive alpha agonist will immediately restore tone
  • No direct pharmacological antagonist is available; support with fluids and vasoconstrictors may be needed
  • Phenoxybenzamine is rapidly dialyzable to reverse effects
  • Beta-blockers will reverse phenoxybenzamine effects

Correct Answer: No direct pharmacological antagonist is available; support with fluids and vasoconstrictors may be needed

Q30. Phenoxybenzamine’s structural property as an alkylating agent accounts for which pharmacological feature?

  • Its reversible binding to receptors
  • Covalent modification of receptor amino acids causing irreversible inhibition
  • Enhanced renal clearance
  • Selective targeting of beta receptors only

Correct Answer: Covalent modification of receptor amino acids causing irreversible inhibition

Q31. In a patient on chronic phenoxybenzamine, blood pressure control wanes when:

  • New alpha receptors are synthesized after drug clearance
  • Drug binding becomes stronger over time
  • Renal clearance of phenoxybenzamine increases
  • Beta receptors are upregulated causing hypertension

Correct Answer: New alpha receptors are synthesized after drug clearance

Q32. Which physiologic response would be expected after administering phenoxybenzamine alone?

  • Increased peripheral vascular resistance
  • Decreased peripheral vascular resistance and reflex tachycardia
  • Primary bronchospasm with bradycardia
  • Marked sodium retention causing hypertension

Correct Answer: Decreased peripheral vascular resistance and reflex tachycardia

Q33. For a B.Pharm student, the primary learning point about phenoxybenzamine’s clinical use is:

  • It is first-line for chronic benign prostatic hyperplasia
  • Its irreversible alpha blockade is useful preoperatively in pheochromocytoma to prevent catecholamine crises
  • It is the preferred acute treatment for myocardial infarction
  • It acts as a diuretic to reduce blood pressure

Correct Answer: Its irreversible alpha blockade is useful preoperatively in pheochromocytoma to prevent catecholamine crises

Q34. Which hemodynamic change is most likely when phenoxybenzamine is given to a hypertensive patient?

  • Increase in systolic and diastolic blood pressure
  • Reduction in blood pressure and postural hypotension risk
  • No change in heart rate or blood pressure
  • Isolated reduction in heart rate without BP change

Correct Answer: Reduction in blood pressure and postural hypotension risk

Q35. Which statement regarding phenoxybenzamine metabolism and elimination is most accurate for practical pharmacy considerations?

  • Its clinical duration is unrelated to plasma levels because of irreversible receptor binding
  • It is cleared only by renal filtration and thus needs dose reduction in hepatic failure
  • Rapid metabolism makes frequent dosing necessary hourly
  • It is a prodrug activated by CYP3A4 only

Correct Answer: Its clinical duration is unrelated to plasma levels because of irreversible receptor binding

Q36. Which sign in a patient with pheochromocytoma suggests insufficient alpha blockade before surgery?

  • Stable blood pressure with no variation
  • Exaggerated hypertensive episodes during tumor manipulation
  • Marked postural hypotension and dizziness
  • Bradycardia unresponsive to atropine

Correct Answer: Exaggerated hypertensive episodes during tumor manipulation

Q37. Phenoxybenzamine can increase cardiac output in some patients primarily by:

  • Direct stimulation of beta-1 receptors
  • Reducing afterload through vasodilation and reflex sympathetic activation
  • Increasing blood viscosity
  • Direct positive inotropy via calcium channels

Correct Answer: Reducing afterload through vasodilation and reflex sympathetic activation

Q38. Which statement about phenoxybenzamine and pregnancy is most appropriate for counseling?

  • It is universally safe and recommended in pregnancy
  • Risk-benefit should be evaluated; use only if clearly needed due to limited human data
  • It is contraindicated during lactation only
  • No precautions are necessary for pregnant patients

Correct Answer: Risk-benefit should be evaluated; use only if clearly needed due to limited human data

Q39. When teaching peers about alpha receptor pharmacology, which comparison is correct?

  • Alpha-1 receptors decrease intracellular Ca2+ when activated
  • Alpha-1 activation increases IP3 and intracellular calcium causing contraction
  • Alpha-2 activation increases cAMP to cause vasoconstriction
  • Alpha receptors are insensitive to catecholamines

Correct Answer: Alpha-1 activation increases IP3 and intracellular calcium causing contraction

Q40. Which of the following is a reasonable counseling point for a patient starting phenoxybenzamine?

  • Avoid sudden position changes to reduce risk of dizziness from orthostatic hypotension
  • You may drive immediately without any caution
  • Expect immediate and short-lived effects only
  • Discontinue the drug abruptly if any mild dizziness occurs

Correct Answer: Avoid sudden position changes to reduce risk of dizziness from orthostatic hypotension

Q41. In the context of drug design, the irreversible nature of phenoxybenzamine suggests what about dosing frequency?

  • Frequent dosing is required because receptors are rapidly regenerated hourly
  • Less frequent dosing may be effective since receptor blockade persists until new receptors are synthesized
  • Dosing frequency must match plasma half-life exactly
  • Continuous infusion is mandatory due to short action

Correct Answer: Less frequent dosing may be effective since receptor blockade persists until new receptors are synthesized

Q42. Which cardiovascular effect would be least expected after phenoxybenzamine administration?

  • Reflex tachycardia
  • Orthostatic hypotension
  • Prominent peripheral vasodilation
  • Marked bronchospasm due to beta-2 blockade

Correct Answer: Marked bronchospasm due to beta-2 blockade

Q43. Which laboratory test provides direct measurement of catecholamine production in pheochromocytoma, often used alongside phenoxybenzamine therapy?

  • Serum troponin
  • Plasma free metanephrines and urinary vanillylmandelic acid (VMA)
  • Serum cortisol only
  • Complete blood count (CBC)

Correct Answer: Plasma free metanephrines and urinary vanillylmandelic acid (VMA)

Q44. If an anesthesiologist gives a high dose of epinephrine to a patient pretreated with phenoxybenzamine, what precaution should be anticipated?

  • Risk of severe hypertension
  • Possible paradoxical hypotension due to unopposed beta-2 vasodilation
  • No hemodynamic changes expected
  • Enhanced epinephrine pressor effect via alpha stimulation

Correct Answer: Possible paradoxical hypotension due to unopposed beta-2 vasodilation

Q45. Which of the following therapeutic agents is most appropriate to treat severe hypotension caused by phenoxybenzamine when vasopressors are required?

  • Phenylephrine (pure alpha-1 agonist)
  • Propranolol (non-selective beta-blocker)
  • Amlodipine (calcium channel blocker)
  • Nitroprusside (vasodilator)

Correct Answer: Phenylephrine (pure alpha-1 agonist)

Q46. For exam-level understanding, which pharmacologic property distinguishes irreversible from reversible antagonists?

  • Irreversible antagonists increase potency of agonists
  • Irreversible antagonists reduce maximal response (efficacy) and cannot be overcome by increasing agonist concentration
  • Reversible antagonists permanently inactivate receptors
  • Reversible antagonists are always non-competitive

Correct Answer: Irreversible antagonists reduce maximal response (efficacy) and cannot be overcome by increasing agonist concentration

Q47. Which side effect of phenoxybenzamine might require discontinuation or dose reduction due to patient intolerance?

  • Mild transient headache
  • Severe symptomatic orthostatic hypotension with syncope
  • Minor nasal stuffiness
  • Temporary metallic taste

Correct Answer: Severe symptomatic orthostatic hypotension with syncope

Q48. When explaining differences between alpha blockers to fellow students, which statement about selectivity is correct?

  • Tamsulosin is non-selective for alpha receptors like phenoxybenzamine
  • Prazosin and tamsulosin are relatively selective for alpha-1 receptors, unlike phenoxybenzamine
  • All alpha blockers are irreversible
  • Phentolamine is a selective alpha-1 irreversible blocker

Correct Answer: Prazosin and tamsulosin are relatively selective for alpha-1 receptors, unlike phenoxybenzamine

Q49. A pharmacology exam question: What is the most likely effect of phenoxybenzamine on sympathetic neurotransmission?

  • Decrease in synaptic norepinephrine due to reuptake inhibition
  • Increase in synaptic norepinephrine due to alpha-2 autoreceptor blockade
  • Complete blockade of catecholamine synthesis
  • Direct agonism at presynaptic beta receptors

Correct Answer: Increase in synaptic norepinephrine due to alpha-2 autoreceptor blockade

Q50. For safe clinical application, key pharmacy advice regarding phenoxybenzamine includes:

  • Ignore postural vitals because they are not affected
  • Advise patients to rise slowly, monitor BP regularly, and be aware of nasal congestion and tachycardia
  • Recommend over-the-counter decongestants routinely to counter nasal effects
  • Tell patients they may stop monitoring once symptoms improve

Correct Answer: Advise patients to rise slowly, monitor BP regularly, and be aware of nasal congestion and tachycardia

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