Direct acting sympathomimetics – Phenylephrine MCQs With Answer

Direct acting sympathomimetics – Phenylephrine MCQs With Answer

Direct acting sympathomimetics like phenylephrine are essential topics in B. Pharm pharmacology. This introduction covers phenylephrine’s mechanism as a selective alpha-1 agonist, clinical uses (nasal decongestant, vasopressor, mydriatic), pharmacokinetics, adverse effects (hypertension, reflex bradycardia, tissue ischemia) and drug interactions (MAO inhibitors, beta-blockers). Understanding receptor selectivity, hemodynamic effects and appropriate routes/doses is vital for pharmacy students preparing for exams and clinical practice. These MCQs emphasize mechanism of action, therapeutic applications, contraindications, monitoring and comparison with other vasopressors. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which receptor subtype is primarily activated by phenylephrine?

• Beta-1 adrenergic receptor
• Alpha-2 adrenergic receptor
• Alpha-1 adrenergic receptor
• Beta-2 adrenergic receptor

Correct Answer: Alpha-1 adrenergic receptor

Q2. The primary therapeutic effect of phenylephrine when given IV is:

• Increased heart rate due to beta-1 stimulation
• Vasodilation and decreased blood pressure
• Potent vasoconstriction leading to increased systemic vascular resistance
• Bronchodilation via beta-2 receptors

Correct Answer: Potent vasoconstriction leading to increased systemic vascular resistance

Q3. A common reflex cardiovascular response to phenylephrine-induced hypertension is:

• Reflex tachycardia
• Reflex bradycardia
• Increased cardiac output
• Ventricular arrhythmias

Correct Answer: Reflex bradycardia

Q4. Phenylephrine is often used as a nasal decongestant because it:

• Blocks histamine receptors in nasal mucosa
• Causes local vasodilation to reduce edema
• Produces vasoconstriction of nasal blood vessels reducing congestion
• Stimulates mucociliary clearance directly

Correct Answer: Produces vasoconstriction of nasal blood vessels reducing congestion

Q5. Compared to epinephrine, phenylephrine has:

• Greater beta-1 agonist activity
• Greater beta-2 agonist activity
• More selective alpha-1 agonist activity
• Equal mixed alpha and beta agonist activity

Correct Answer: More selective alpha-1 agonist activity

Q6. Which adverse effect is most likely with excessive systemic phenylephrine administration?

• Hypotension due to vasodilation
• Tissue necrosis at extravasation site
• Severe bronchodilation
• Hyperglycemia from beta-2 stimulation

Correct Answer: Tissue necrosis at extravasation site

Q7. The primary metabolic enzyme responsible for phenylephrine breakdown is:

• CYP3A4
• Monoamine oxidase (MAO)
• Acetylcholinesterase
• COMT (catechol-O-methyltransferase)

Correct Answer: Monoamine oxidase (MAO)

Q8. Oral phenylephrine as a decongestant has limited efficacy mainly due to:

• Rapid renal excretion unchanged
• Poor receptor affinity
• Extensive first-pass metabolism by MAO
• Inactivation by gastric acid

Correct Answer: Extensive first-pass metabolism by MAO

Q9. In anesthesia-induced hypotension without tachycardia, phenylephrine is preferred because it:

• Increases heart rate and contractility
• Provides pure vasoconstriction raising blood pressure
• Produces significant bronchodilation
• Has long duration of action to maintain BP

Correct Answer: Provides pure vasoconstriction raising blood pressure

Q10. Which patient is at highest risk of adverse effects from topical ocular phenylephrine?

• Patient with open-angle glaucoma
• Patient with narrow-angle glaucoma
• Patient with dry eye syndrome
• Contact lens wearer

Correct Answer: Patient with narrow-angle glaucoma

Q11. Phenylephrine increases mean arterial pressure primarily by:

• Increasing stroke volume directly
• Decreasing peripheral vascular resistance
• Increasing systemic vascular resistance through alpha-1 vasoconstriction
• Stimulating renin release to increase blood volume

Correct Answer: Increasing systemic vascular resistance through alpha-1 vasoconstriction

Q12. Which drug interaction can potentiate the hypertensive effects of phenylephrine?

• Concurrent use of nitrates
• Monoamine oxidase inhibitors (MAOIs)
• Atenolol (selective beta-1 blocker)
• Loop diuretics

Correct Answer: Monoamine oxidase inhibitors (MAOIs)

Q13. Phenylephrine is contraindicated or should be used with caution in patients with:

• Hypotension due to distributive shock where vasoconstriction is harmful
• Severe bradycardia and hypertension risk
• Hypovolemia where increase in afterload worsens perfusion
• All of the above

Correct Answer: All of the above

Q14. Which of the following describes phenylephrine’s effect on cardiac output in most patients?

• Increases cardiac output by direct beta stimulation
• Decreases cardiac output due to increased afterload and reflex bradycardia
• Has no effect on cardiac output
• Increases cardiac output by increasing venous return

Correct Answer: Decreases cardiac output due to increased afterload and reflex bradycardia

Q15. The mechanism by which phenylephrine causes mydriasis is:

• Direct stimulation of iris sphincter muscle via muscarinic receptors
• Alpha-1 mediated contraction of the radial dilator muscle of the iris
• Beta-2 mediated relaxation of the ciliary muscle
• Inhibition of aqueous humor production

Correct Answer: Alpha-1 mediated contraction of the radial dilator muscle of the iris

Q16. Which monitoring parameter is most important when starting an IV phenylephrine infusion in ICU?

• Serum potassium level
• Noninvasive or invasive blood pressure and heart rate
• Pulse oximetry only
• Liver function tests

Correct Answer: Noninvasive or invasive blood pressure and heart rate

Q17. Compared to phenylephrine, norepinephrine has which major pharmacologic difference?

• Norepinephrine has greater beta-1 agonist activity increasing heart rate and contractility
• Norepinephrine is more selective for alpha-1 only
• Norepinephrine is a pure beta-2 agonist
• Norepinephrine does not affect systemic vascular resistance

Correct Answer: Norepinephrine has greater beta-1 agonist activity increasing heart rate and contractility

Q18. In management of local extravasation of phenylephrine, the recommended immediate action is:

• Apply warm compresses and elevate the limb
• Inject phentolamine locally to reverse vasoconstriction
• Apply ice packs and immobilize
• Give systemic beta-blocker

Correct Answer: Inject phentolamine locally to reverse vasoconstriction

Q19. Which clinical situation is phenylephrine commonly used as a bolus to treat?

• Acute bronchospasm in asthma
• Anaphylactic shock as first-line therapy
• Transient hypotension during spinal anesthesia
• Hyperthyroid-induced tachycardia

Correct Answer: Transient hypotension during spinal anesthesia

Q20. Topical phenylephrine for nasal congestion may cause systemic hypertension because:

• Topical agents cannot enter the systemic circulation
• High doses or frequent use lead to systemic absorption and alpha-1 mediated vasoconstriction
• They release histamine causing vascular effects
• They block alpha-1 receptors causing reflex responses

Correct Answer: High doses or frequent use lead to systemic absorption and alpha-1 mediated vasoconstriction

Q21. Which statement about phenylephrine’s selectivity is correct?

• Phenylephrine is a non-selective adrenergic agonist
• Phenylephrine selectively activates alpha-1 receptors with minimal beta activity
• Phenylephrine primarily activates beta-2 receptors
• Phenylephrine is an indirect sympathomimetic relying on NE release

Correct Answer: Phenylephrine selectively activates alpha-1 receptors with minimal beta activity

Q22. When switching from ephedrine to phenylephrine for treating hypotension in a patient on a beta-blocker, you should expect:

• Greater increase in heart rate with phenylephrine
• Less effectiveness because phenylephrine relies on endogenous catecholamines
• Pronounced increase in blood pressure due to unopposed alpha action
• No hemodynamic difference between agents

Correct Answer: Pronounced increase in blood pressure due to unopposed alpha action

Q23. Which formulation route of phenylephrine produces the fastest onset of action?

• Oral tablets
• Topical nasal spray
• Intravenous injection
• Topical ocular drops

Correct Answer: Intravenous injection

Q24. In a patient with coronary artery disease, phenylephrine-induced reflex bradycardia can be harmful because:

• Increased heart rate increases myocardial oxygen demand
• Bradycardia reduces coronary perfusion time and may worsen ischemia
• Bradycardia always improves myocardial perfusion
• Phenylephrine directly causes coronary vasodilation

Correct Answer: Bradycardia reduces coronary perfusion time and may worsen ischemia

Q25. Which of the following drugs would most likely antagonize phenylephrine’s vasoconstrictive effects?

• Phentolamine (alpha antagonist)
• Propranolol (beta-blocker)
• Phenobarbital
• Diltiazem (calcium channel blocker)

Correct Answer: Phentolamine (alpha antagonist)

Q26. Phenylephrine is often preferred over epinephrine in some surgical settings because it:

• Produces more tachycardia which is desired
• Has shorter duration of action and is more selective for alpha receptors
• Is a potent bronchodilator
• Increases renin release strongly

Correct Answer: Has shorter duration of action and is more selective for alpha receptors

Q27. Which side effect is commonly seen with prolonged topical nasal use of phenylephrine?

• Rhinitis medicamentosa (rebound congestion)
• Nasal mucosa anesthesia
• Permanent anosmia
• Increased mucociliary clearance

Correct Answer: Rhinitis medicamentosa (rebound congestion)

Q28. In patients taking tricyclic antidepressants (TCAs), phenylephrine may cause exaggerated pressor response because TCAs:

• Block MAO leading to reduced metabolism of phenylephrine
• Potentiate alpha receptor activation directly
• Interfere with catecholamine uptake and potentiate sympathomimetics
• Induce hepatic enzymes that increase phenylephrine clearance

Correct Answer: Interfere with catecholamine uptake and potentiate sympathomimetics

Q29. The duration of action after an IV bolus of phenylephrine is approximately:

• 12–24 hours
• 4–6 hours
• 15–30 minutes
• 1–2 minutes

Correct Answer: 15–30 minutes

Q30. Which pharmacodynamic effect explains phenylephrine’s ability to increase systolic blood pressure with minimal change in pulse pressure?

• Increase in cardiac contractility
• Peripheral vasoconstriction raising diastolic pressure more than systolic
• Direct increase in stroke volume only
• Increased venous capacitance reducing preload

Correct Answer: Peripheral vasoconstriction raising diastolic pressure more than systolic

Q31. Phenylephrine’s mechanism is best classified as which of the following?

• Indirect sympathomimetic that releases norepinephrine
• Direct selective alpha-1 adrenergic receptor agonist
• Direct beta-2 receptor agonist
• Cholinergic agonist

Correct Answer: Direct selective alpha-1 adrenergic receptor agonist

Q32. In septic shock with profound vasodilation and tachycardia, phenylephrine may not be ideal as first-line because:

• It reduces heart rate and may decrease cardiac output in tachycardic patients
• It causes bronchospasm
• It has strong beta-1 activity increasing arrhythmia risk
• It causes diuresis worsening hypotension

Correct Answer: It reduces heart rate and may decrease cardiac output in tachycardic patients

Q33. Which laboratory or bedside finding would suggest excessive alpha-1 mediated vasoconstriction from phenylephrine?

• Decreased systemic vascular resistance on hemodynamic monitor
• Marked increase in blood pressure and decreased heart rate
• Widened pulse pressure with tachycardia
• Elevated serum potassium

Correct Answer: Marked increase in blood pressure and decreased heart rate

Q34. For topical ocular use, phenylephrine is primarily used to:

• Reduce intraocular pressure in glaucoma
• Induce mydriasis for retinal examination
• Treat conjunctivitis due to bacteria
• Lubricate the cornea

Correct Answer: Induce mydriasis for retinal examination

Q35. Which of the following is a correct statement about phenylephrine and pregnancy?

• Phenylephrine is absolutely contraindicated in all trimesters
• Phenylephrine may be used with caution when benefits outweigh risks, especially as a vasopressor in obstetric anesthesia
• Phenylephrine causes teratogenic effects in early pregnancy
• Phenylephrine is the preferred oral decongestant in pregnancy

Correct Answer: Phenylephrine may be used with caution when benefits outweigh risks, especially as a vasopressor in obstetric anesthesia

Q36. Which monitoring is particularly important when phenylephrine is administered to a patient with peripheral vascular disease?

• Serum creatinine only
• Inspection and perfusion of distal extremities for ischemia
• Serial liver enzymes
• Neurologic reflex testing

Correct Answer: Inspection and perfusion of distal extremities for ischemia

Q37. Which statement accurately contrasts phenylephrine and ephedrine in obstetric anesthesia?

• Phenylephrine increases maternal heart rate more than ephedrine
• Ephedrine crosses the placenta less than phenylephrine
• Phenylephrine reduces maternal heart rate and maintains blood pressure without increasing fetal acidosis as much as ephedrine
• Ephedrine is a pure alpha-1 agonist whereas phenylephrine is indirect

Correct Answer: Phenylephrine reduces maternal heart rate and maintains blood pressure without increasing fetal acidosis as much as ephedrine

Q38. A patient taking a nonselective beta-blocker receives phenylephrine. What is the expected effect?

• Attenuated alpha response leading to hypotension
• Unopposed alpha vasoconstriction causing marked hypertension
• Enhanced bronchodilation
• No change in hemodynamic response

Correct Answer: Unopposed alpha vasoconstriction causing marked hypertension

Q39. Which of the following best describes why oral phenylephrine is less effective than pseudoephedrine?

• Pseudoephedrine has better alpha-1 selectivity than phenylephrine
• Pseudoephedrine is resistant to MAO breakdown and has better oral bioavailability
• Pseudoephedrine is a beta-2 agonist while phenylephrine is alpha-1
• Pseudoephedrine causes less tachyphylaxis than phenylephrine

Correct Answer: Pseudoephedrine is resistant to MAO breakdown and has better oral bioavailability

Q40. Which adverse effect should pharmacists counsel patients about when dispensing topical phenylephrine nasal sprays?

• Risk of sedation and drowsiness
• Possibility of rebound congestion with prolonged use
• Permanent loss of smell within hours
• Increased appetite and weight gain

Correct Answer: Possibility of rebound congestion with prolonged use

Q41. Which hemodynamic profile is most consistent with phenylephrine infusion during surgery?

• Increased MAP, increased HR, increased CO
• Increased MAP, decreased HR, decreased CO
• Decreased MAP, increased HR, increased CO
• No change in MAP, increased HR

Correct Answer: Increased MAP, decreased HR, decreased CO

Q42. Which pharmacologic property explains phenylephrine’s low oral bioavailability?

• High lipid solubility and rapid absorption
• Extensive first-pass metabolism by monoamine oxidase in gut and liver
• Strong binding to plasma proteins preventing absorption
• Immediate renal excretion before absorption

Correct Answer: Extensive first-pass metabolism by monoamine oxidase in gut and liver

Q43. For a patient with tachyarrhythmia and refractory hypotension, phenylephrine may be chosen because it:

• Increases heart rate to correct arrhythmia
• Raises blood pressure without further increasing heart rate
• Acts as an antiarrhythmic agent
• Has predominant beta-1 effects improving rhythm

Correct Answer: Raises blood pressure without further increasing heart rate

Q44. Which statement about the pharmacokinetics of phenylephrine is true?

• It is primarily metabolized by CYP450 enzymes
• It undergoes extensive metabolism by MAO and has short half-life
• It accumulates significantly with repeated dosing due to long half-life
• It is excreted unchanged in large amounts in urine

Correct Answer: It undergoes extensive metabolism by MAO and has short half-life

Q45. In overdose of phenylephrine presenting with severe hypertension and bradycardia, an appropriate antidote is:

• IV glucagon
• IV nitroprusside or phentolamine to reduce blood pressure
• Oral activated charcoal only
• IV atropine to treat hypertension

Correct Answer: IV nitroprusside or phentolamine to reduce blood pressure

Q46. Which statement about phenylephrine use in elderly patients is most appropriate?

• Elderly patients are less sensitive to alpha agonists and need higher doses
• They are more susceptible to hypertensive responses and ischemia, so use lower doses and monitor closely
• Phenylephrine has no special precautions in elderly
• It is contraindicated in all patients over 65

Correct Answer: They are more susceptible to hypertensive responses and ischemia, so use lower doses and monitor closely

Q47. Which is a rational counseling point for patients using oral phenylephrine products?

• Expect long-lasting relief for several days with a single dose
• Avoid MAO inhibitors and seek advice if on antidepressant therapy
• No interactions are expected with other medications
• It can be used safely without limits for chronic nasal congestion

Correct Answer: Avoid MAO inhibitors and seek advice if on antidepressant therapy

Q48. Which laboratory finding might be seen after significant peripheral vasoconstriction due to phenylephrine extravasation?

• Localized metabolic acidosis in affected tissue and signs of ischemia
• Systemic metabolic alkalosis
• Hypokalemia due to intracellular shift in entire body
• Elevated hemoglobin due to hemolysis

Correct Answer: Localized metabolic acidosis in affected tissue and signs of ischemia

Q49. Which advantage does phenylephrine have as a vasopressor in anesthesia for hypotension due to spinal block?

• It increases heart rate to correct bradycardia from the block
• It restores vascular tone without increasing myocardial oxygen consumption significantly
• It is the only safe vasopressor during pregnancy
• It has strong inotropic effects improving contractility

Correct Answer: It restores vascular tone without increasing myocardial oxygen consumption significantly

Q50. Which clinical scenario would favor using phenylephrine over dopamine for hypotension?

• Cardiogenic shock with low cardiac contractility
• Hypotension with reflex tachycardia where heart rate should not be increased
• Bradycardia requiring inotropic support
• Severe renal hypoperfusion requiring dopaminergic renal vasodilation

Correct Answer: Hypotension with reflex tachycardia where heart rate should not be increased

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