Alpha adrenergic blockers – Phentolamine MCQs With Answer

Alpha adrenergic blockers – Phentolamine MCQs With Answer

Phentolamine is a nonselective alpha-adrenergic blocker important in B.Pharm pharmacology for understanding receptor antagonism, vascular smooth muscle effects, and clinical applications. This concise guide covers mechanism of action (alpha-1 and alpha-2 blockade), pharmacodynamics, indications such as pheochromocytoma diagnosis, hypertensive emergencies and norepinephrine extravasation, pharmacokinetics, adverse effects like orthostatic hypotension and reflex tachycardia, and key drug interactions including epinephrine reversal. These MCQs emphasize clinical reasoning, mechanism-based predictions, and exam-focused facts to help B.Pharm students master phentolamine and alpha-adrenergic pharmacology. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary mechanism of action of phentolamine?

• Selective alpha-1 receptor agonist
• Nonselective alpha-1 and alpha-2 receptor antagonist
• Beta-1 receptor antagonist
• Monoamine oxidase inhibitor

Correct Answer: Nonselective alpha-1 and alpha-2 receptor antagonist

Q2. Phentolamine’s blockade of presynaptic alpha-2 receptors results in which immediate effect?

• Decreased norepinephrine release
• Increased norepinephrine release
• Direct beta receptor stimulation
• Reduced acetylcholine release

Correct Answer: Increased norepinephrine release

Q3. Which clinical use is phentolamine most commonly associated with?

• Long-term treatment of chronic hypertension
• Acute management of catecholamine-induced hypertensive crisis (e.g., pheochromocytoma)
• First-line therapy for heart failure
• Maintenance therapy for bronchial asthma

Correct Answer: Acute management of catecholamine-induced hypertensive crisis (e.g., pheochromocytoma)

Q4. How does phentolamine cause reflex tachycardia?

• Direct stimulation of the sinoatrial node
• Baroreceptor-mediated response to vasodilation
• Inhibition of sympathetic outflow from the CNS
• Activation of vagal tone

Correct Answer: Baroreceptor-mediated response to vasodilation

Q5. Which adverse effect is most characteristic of phentolamine therapy?

• Bradycardia with hypotension
• Orthostatic hypotension and tachycardia
• Severe bronchospasm
• Hyperkalemia

Correct Answer: Orthostatic hypotension and tachycardia

Q6. Phentolamine is useful in treating extravasation of which drug?

• Insulin
• Norepinephrine
• Furosemide
• Heparin

Correct Answer: Norepinephrine

Q7. Compared to phenoxybenzamine, phentolamine is:

• Irreversible alpha blocker with longer duration
• Reversible alpha blocker with shorter duration
• Beta-selective blocker
• MAO inhibitor

Correct Answer: Reversible alpha blocker with shorter duration

Q8. Which phenomenon describes the increased blood pressure response to epinephrine after phentolamine administration?

• Epinephrine reversal
• Alpha-agonist potentiation
• Beta-blocker effect
• Synergistic vasoconstriction

Correct Answer: Epinephrine reversal

Q9. In epinephrine reversal caused by alpha blockade, what happens to diastolic blood pressure?

• Increases due to alpha stimulation
• Decreases due to unopposed beta-2 vasodilation
• Remains unchanged
• Becomes erratic without pattern

Correct Answer: Decreases due to unopposed beta-2 vasodilation

Q10. Which route of administration is commonly used for phentolamine in acute settings?

• Oral tablet once daily
• Intravenous or intramuscular injection
• Topical cream
• Inhalation aerosol

Correct Answer: Intravenous or intramuscular injection

Q11. Which receptor blockade of phentolamine contributes to increased gastrointestinal motility?

• Beta-2 blockade
• Alpha-1 blockade
• Cholinergic receptor activation
• Histamine H2 blockade

Correct Answer: Alpha-1 blockade

Q12. Which laboratory or clinical test can help diagnose pheochromocytoma prior to phentolamine use?

• Serum troponin
• 24-hour urinary catecholamines and metanephrines
• Fasting blood glucose
• Serum creatinine clearance

Correct Answer: 24-hour urinary catecholamines and metanephrines

Q13. Why must phentolamine be used cautiously in patients with coronary artery disease?

• It causes severe coronary vasospasm
• Reflex tachycardia may increase myocardial oxygen demand and provoke ischemia
• It significantly raises LDL cholesterol
• It suppresses cardiac contractility directly

Correct Answer: Reflex tachycardia may increase myocardial oxygen demand and provoke ischemia

Q14. Which effect is due to blockade of postsynaptic alpha-1 receptors by phentolamine?

• Vasoconstriction of arterioles
• Vasodilation of arterioles and decreased peripheral resistance
• Increased platelet aggregation
• Bronchoconstriction

Correct Answer: Vasodilation of arterioles and decreased peripheral resistance

Q15. Phentolamine is contraindicated or used with caution in which condition?

• Pheochromocytoma diagnosis
• Severe hypotension or hypovolemia
• Hypertensive emergency with catecholamine excess
• Norepinephrine extravasation

Correct Answer: Severe hypotension or hypovolemia

Q16. The onset of action for IV phentolamine is:

• Several hours
• Within 1–2 minutes
• After 24 hours
• Delayed until metabolized in the liver

Correct Answer: Within 1–2 minutes

Q17. Phentolamine may cause nasal congestion due to blockade of which receptors in nasal mucosa?

• Beta-1 receptors
• Alpha-1 receptors
• Muscarinic receptors
• Histamine H1 receptors

Correct Answer: Alpha-1 receptors

Q18. Which statement best contrasts phentolamine and phenoxybenzamine?

• Phentolamine is irreversible; phenoxybenzamine is reversible
• Both are selective beta blockers
• Phentolamine is reversible and shorter acting; phenoxybenzamine is irreversible and longer acting
• Phenoxybenzamine blocks only beta receptors

Correct Answer: Phentolamine is reversible and shorter acting; phenoxybenzamine is irreversible and longer acting

Q19. Which drug interaction is most important to remember with phentolamine?

• Synergistic hypotension with nitrates
• Severe hyperkalemia with ACE inhibitors
• Prolonged QT with macrolides
• Decreased effect of diuretics

Correct Answer: Synergistic hypotension with nitrates

Q20. Why can phentolamine produce diarrhea as a side effect?

• It inhibits gut smooth muscle activity
• Alpha blockade increases parasympathetic-mediated GI motility
• It causes intestinal ischemia
• It blocks serotonin receptors in the gut

Correct Answer: Alpha blockade increases parasympathetic-mediated GI motility

Q21. During surgical removal of a pheochromocytoma, phentolamine is used primarily to:

• Decrease intraoperative bleeding via vasoconstriction
• Control blood pressure by preventing catecholamine-mediated vasoconstriction
• Suppress infection risk
• Act as an anxiolytic

Correct Answer: Control blood pressure by preventing catecholamine-mediated vasoconstriction

Q22. What is the expected effect of phentolamine on peripheral vascular resistance (PVR)?

• PVR increases
• PVR decreases
• PVR is unchanged
• PVR fluctuates unpredictably

Correct Answer: PVR decreases

Q23. Which cardiovascular parameter often rises after phentolamine despite lowered blood pressure?

• Systemic vascular resistance
• Heart rate
• Central venous pressure
• Left ventricular ejection fraction

Correct Answer: Heart rate

Q24. A pharmacology student should recall that phentolamine is classified pharmacologically as a(n):

• Alpha-adrenergic agonist
• Alpha-adrenergic antagonist
• Calcium channel blocker
• ACE inhibitor

Correct Answer: Alpha-adrenergic antagonist

Q25. Which effect would you predict if phentolamine is administered prior to epinephrine?

• Epinephrine’s pressor effect is enhanced
• Epinephrine produces a fall in diastolic pressure and a reduced or reversed pressor response
• Epinephrine causes massive bradycardia
• No interaction occurs

Correct Answer: Epinephrine produces a fall in diastolic pressure and a reduced or reversed pressor response

Q26. In the management of hypertensive crisis due to clonidine withdrawal, phentolamine would likely:

• Worsen hypertension by blocking alpha receptors
• Lower blood pressure by direct alpha blockade
• Be ineffective because clonidine acts on beta receptors
• Cause bronchospasm

Correct Answer: Lower blood pressure by direct alpha blockade

Q27. Which monitoring parameter is essential when administering IV phentolamine?

• Pulse oximetry only
• Continuous blood pressure and heart rate monitoring
• Serum potassium every hour
• Coagulation profile

Correct Answer: Continuous blood pressure and heart rate monitoring

Q28. Phentolamine’s effect on insulin secretion is best described as:

• Stimulates insulin release by alpha-2 blockade
• Inhibits insulin release by blocking islet beta receptors
• No effect on insulin release
• Causes insulin destruction

Correct Answer: Stimulates insulin release by alpha-2 blockade

Q29. Which of the following is a correct statement about phentolamine’s duration of action?

• It is long-acting (days) after a single dose
• It has a short duration and requires repeated dosing or infusion in acute care
• It is stored in fat and released slowly over weeks
• It irreversibly binds to alpha receptors for life

Correct Answer: It has a short duration and requires repeated dosing or infusion in acute care

Q30. Which sign suggests excessive alpha blockade by phentolamine during therapy?

• Severe hypertension and bradycardia
• Marked orthostatic hypotension and dizziness
• Progressive hyperreflexia
• Oliguria due to renal vasoconstriction

Correct Answer: Marked orthostatic hypotension and dizziness

Q31. Phentolamine’s chemical classification belongs to which drug family?

• Imidazoline derivatives
• Phenylethylamines
• Azole antifungals
• Sulfonylureas

Correct Answer: Imidazoline derivatives

Q32. Which physiological response is expected in skeletal muscle blood vessels after phentolamine administration?

• Vasoconstriction due to alpha stimulation
• Vasodilation due to alpha-1 blockade
• Unchanged tone because phentolamine targets only cardiac receptors
• Immediate thrombosis

Correct Answer: Vasodilation due to alpha-1 blockade

Q33. For extravasation treatment of norepinephrine, how should phentolamine be administered?

• Systemic oral dose only
• Local infiltration around the extravasation site
• Topical application over the area
• Give beta-blocker instead

Correct Answer: Local infiltration around the extravasation site

Q34. Which hemodynamic effect differentiates alpha-1 blockade from combined alpha-1/alpha-2 blockade?

• Only alpha-1 blockade causes reflex tachycardia
• Combined blockade (alpha-1 and alpha-2) often causes greater tachycardia due to increased norepinephrine release
• Alpha-1 blockade increases blood pressure
• Alpha-2 blockade reduces heart rate

Correct Answer: Combined blockade (alpha-1 and alpha-2) often causes greater tachycardia due to increased norepinephrine release

Q35. Which patient history would prompt caution before giving phentolamine?

• History of migraine headaches
• History of recent myocardial infarction and unstable angina
• Seasonal allergic rhinitis
• History of peptic ulcer disease

Correct Answer: History of recent myocardial infarction and unstable angina

Q36. A pharmacology exam question: phentolamine reduces peripheral resistance primarily by blocking:

• Beta-2 receptors in skeletal muscle vessels
• Presynaptic dopamine receptors
• Postsynaptic alpha-1 receptors on vascular smooth muscle
• Renin release from the kidney

Correct Answer: Postsynaptic alpha-1 receptors on vascular smooth muscle

Q37. Which effect on renin secretion might be seen with phentolamine?

• Marked increase in renin due to decreased renal perfusion only
• Potential increase in renin secondary to lowered blood pressure
• Complete inhibition of renin release
• No change in renin at all times

Correct Answer: Potential increase in renin secondary to lowered blood pressure

Q38. In drug comparison, which agent is more selective for alpha-1 receptors than phentolamine?

• Prazosin
• Phenoxybenzamine
• Isoproterenol
• Propranolol

Correct Answer: Prazosin

Q39. Which statement is true regarding phentolamine and sexual function?

• It may be used intracavernosally to treat erectile dysfunction by increasing blood flow
• It causes permanent impotence
• It enhances libido centrally as its primary effect
• It is contraindicated in erectile dysfunction because it reduces penile blood flow

Correct Answer: It may be used intracavernosally to treat erectile dysfunction by increasing blood flow

Q40. What effect does phentolamine have on hepatic blood flow?

• Marked vasoconstriction of hepatic arteries
• Increased perfusion due to systemic vasodilation, but effects are variable
• Complete shutdown of hepatic circulation
• Selective increase in portal pressure only

Correct Answer: Increased perfusion due to systemic vasodilation, but effects are variable

Q41. Which pharmacokinetic property is important for IV phentolamine use?

• Extensive oral bioavailability makes IV unnecessary
• Rapid onset and short duration suitable for titratable IV infusion
• Long half-life permits once-weekly dosing
• Requires hepatic activation to be effective

Correct Answer: Rapid onset and short duration suitable for titratable IV infusion

Q42. Combining phentolamine with a beta-blocker may result in:

• Reduced reflex tachycardia but risk of unopposed alpha effects if not properly sequenced
• Severe bronchodilation
• Complete loss of antihypertensive effect
• Marked increase in peripheral resistance only

Correct Answer: Reduced reflex tachycardia but risk of unopposed alpha effects if not properly sequenced

Q43. Which sign distinguishes alpha-2 blockade from alpha-1 blockade clinically?

• Alpha-2 blockade reduces norepinephrine release
• Alpha-2 blockade increases norepinephrine release leading to more pronounced tachycardia
• Alpha-2 blockade causes vasoconstriction directly
• Alpha-2 blockade causes bradycardia via vagal stimulation

Correct Answer: Alpha-2 blockade increases norepinephrine release leading to more pronounced tachycardia

Q44. In overdose of phentolamine, the first-line supportive measure is:

• Administer intravenous fluids and vasopressors as needed for hypotension
• Immediate dialysis to remove the drug
• Give high-dose beta-agonists only
• Administer activated charcoal for IV overdose

Correct Answer: Administer intravenous fluids and vasopressors as needed for hypotension

Q45. Which change in reflexes or sympathetic activity might be observed after phentolamine?

• Decreased sympathetic tone with reduced reflex tachycardia
• Increased sympathetic outflow signs like sweating and tachycardia due to presynaptic alpha-2 blockade
• Complete autonomic failure
• Selective parasympathetic dominance without other effects

Correct Answer: Increased sympathetic outflow signs like sweating and tachycardia due to presynaptic alpha-2 blockade

Q46. Which condition is NOT an accepted clinical indication for phentolamine?

• Treating hypertensive episodes from pheochromocytoma
• Local treatment of catecholamine extravasation
• Chronic long-term management of benign prostatic hyperplasia (BPH)
• Diagnostic blockade for pheochromocytoma testing

Correct Answer: Chronic long-term management of benign prostatic hyperplasia (BPH)

Q47. Which monitoring parameter should be adjusted carefully because phentolamine can increase it indirectly?

• Blood glucose levels due to increased insulin secretion
• Serum sodium due to antidiuretic effects
• Serum creatinine due to direct nephrotoxicity
• Serum calcium due to parathyroid stimulation

Correct Answer: Blood glucose levels due to increased insulin secretion

Q48. Phentolamine causes which change in skin blood flow?

• Decreased skin perfusion causing pallor
• Increased cutaneous blood flow producing flushing
• Complete vascular necrosis
• No effect on skin circulation

Correct Answer: Increased cutaneous blood flow producing flushing

Q49. Which would be a correct exam-style statement: phentolamine may precipitate myocardial ischemia in vulnerable patients because:

• It directly reduces coronary perfusion pressure by vasoconstricting coronary arteries
• Reflex tachycardia increases myocardial oxygen demand while lowering diastolic blood pressure and coronary perfusion
• It causes severe anemia
• It blocks calcium channels in cardiac myocytes

Correct Answer: Reflex tachycardia increases myocardial oxygen demand while lowering diastolic blood pressure and coronary perfusion

Q50. A final key point: which pharmacological property makes phentolamine especially useful in acute care settings?

• Slow onset and prolonged effect allow for once-daily dosing
• Rapid, reversible alpha blockade that can be titrated IV for short-term control
• High oral bioavailability for outpatient use
• Selective beta-blocking properties

Correct Answer: Rapid, reversible alpha blockade that can be titrated IV for short-term control

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