Introduction: Sympathomimetics are adrenergic agonists that stimulate sympathetic nervous system receptors (alpha, beta, and beta3), producing effects such as vasoconstriction, bronchodilation, and increased cardiac output. This topic covers catecholamines (epinephrine, norepinephrine, dopamine) versus non‑catecholamines (phenylephrine, ephedrine), receptor selectivity, mechanisms (direct vs indirect), metabolism by MAO and COMT, clinical uses, adverse effects, drug interactions, and principles of receptor desensitization—essential for B.Pharm students in pharmacology and therapeutics. Understanding pharmacokinetics, selectivity, and safety is critical for safe drug use and counseling. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which property best distinguishes catecholamines from non-catecholamine sympathomimetics?
- Catecholamines are resistant to monoamine oxidase (MAO)
- Catecholamines have a catechol ring and are rapidly metabolized by COMT
- Non-catecholamines produce tachyphylaxis more rapidly
- Non-catecholamines cannot cross the blood–brain barrier
Correct Answer: Catecholamines have a catechol ring and are rapidly metabolized by COMT
Q2. Epinephrine’s primary receptor activity at low therapeutic doses is best described as:
- Selective alpha-1 agonism causing vasoconstriction only
- Predominant beta-2 agonism with bronchodilation and vasodilation
- Pure beta-1 agonism increasing heart rate without vascular effects
- Alpha-2 agonism decreasing sympathetic outflow
Correct Answer: Predominant beta-2 agonism with bronchodilation and vasodilation
Q3. Which sympathomimetic is preferred for anaphylactic shock due to combined alpha and beta actions?
- Phenylephrine
- Isoproterenol
- Epinephrine
- Dobutamine
Correct Answer: Epinephrine
Q4. The mechanism by which amphetamine produces sympathomimetic effects is mainly:
- Direct agonism of beta-2 receptors in bronchial smooth muscle
- Inhibition of COMT leading to increased circulating catecholamines
- Promotion of norepinephrine release from presynaptic terminals and reuptake inhibition
- Selective activation of peripheral alpha-1 receptors only
Correct Answer: Promotion of norepinephrine release from presynaptic terminals and reuptake inhibition
Q5. Which agent is a selective alpha-1 agonist commonly used as a decongestant and for hypotension?
- Clonidine
- Phenylephrine
- Dobutamine
- Isoproterenol
Correct Answer: Phenylephrine
Q6. A patient on a monoamine oxidase inhibitor (MAOI) should avoid which sympathomimetic oral decongestant due to risk of hypertensive crisis?
- Pseudoephedrine
- Terbutaline
- Mirabegron
- Brimonidine
Correct Answer: Pseudoephedrine
Q7. Which statement about dopamine at low, moderate, and high doses is correct?
- Low doses: alpha-1 vasoconstriction; high doses: beta-2 vasodilation
- Low doses: dopamine receptor-mediated renal vasodilation; moderate: beta-1 inotropy; high: alpha-1 vasoconstriction
- It is a highly selective beta-2 agonist at all doses
- Dopamine is not metabolized by MAO or COMT
Correct Answer: Low doses: dopamine receptor-mediated renal vasodilation; moderate: beta-1 inotropy; high: alpha-1 vasoconstriction
Q8. Dobutamine is primarily used in cardiogenic shock because it:
- Is a potent alpha-1 agonist reducing preload
- Acts mainly as a beta-1 agonist increasing contractility with minimal heart rate increase
- Inhibits NE reuptake causing sustained hypertension
- Causes selective diuresis via dopamine receptors
Correct Answer: Acts mainly as a beta-1 agonist increasing contractility with minimal heart rate increase
Q9. Which term best describes drugs like ephedrine that both directly stimulate adrenergic receptors and release endogenous catecholamines?
- Pure direct agonists
- Indirect sympatholytics
- Mixed-acting sympathomimetics
- Beta-blockers with intrinsic activity
Correct Answer: Mixed-acting sympathomimetics
Q10. Chronic exposure to beta-2 agonists can lead to decreased receptor responsiveness due to:
- Upregulation of receptor synthesis
- COMT-mediated receptor degradation
- Receptor desensitization and downregulation via GRK and beta-arrestin pathways
- Increased acetylcholine release counteracting effects
Correct Answer: Receptor desensitization and downregulation via GRK and beta-arrestin pathways
Q11. Which drug is a selective beta-3 agonist used to relax the detrusor muscle in overactive bladder?
- Mirabegron
- Salmeterol
- Phenylephrine
- Clonidine
Correct Answer: Mirabegron
Q12. A patient with asthma needs a short-acting bronchodilator for acute relief. The best sympathomimetic choice is:
- Salmeterol
- Formoterol
- Albuterol (salbutamol)
- Isoproterenol for daily maintenance
Correct Answer: Albuterol (salbutamol)
Q13. Which side effect is most characteristic of alpha-1 agonists such as phenylephrine?
- Reflex bradycardia due to increased blood pressure
- Hypoglycemia due to increased insulin release
- Bronchoconstriction leading to wheeze
- Urinary incontinence due to bladder relaxation
Correct Answer: Reflex bradycardia due to increased blood pressure
Q14. In the treatment of septic shock with hypotension and low systemic vascular resistance, which sympathomimetic is commonly used to increase vascular tone?
- Norepinephrine
- Isoproterenol
- Propranolol
- Doxazosin
Correct Answer: Norepinephrine
Q15. Which pharmacokinetic property explains why epinephrine cannot be given orally for systemic effects?
- Poor absorption from GI tract due to high lipophilicity
- Extensive first-pass metabolism by MAO and COMT in the gut and liver
- Extreme renal elimination within minutes after oral ingestion
- Large molecular size preventing absorption
Correct Answer: Extensive first-pass metabolism by MAO and COMT in the gut and liver
Q16. Clonidine lowers blood pressure primarily by which mechanism?
- Direct peripheral alpha-1 stimulation causing vasodilation
- Central alpha-2 agonism reducing sympathetic outflow
- Beta-1 blockade in the heart reducing contractility
- Increasing renal dopamine release to promote natriuresis
Correct Answer: Central alpha-2 agonism reducing sympathetic outflow
Q17. Which sympathomimetic would most likely worsen hyperthyroid-associated tachycardia and is generally contraindicated?
- Alpha-1 selective agents like phenylephrine
- Nonselective beta agonist isoproterenol
- Beta-1 selective agonist dobutamine
- Topical alpha-2 agonist brimonidine
Correct Answer: Nonselective beta agonist isoproterenol
Q18. A drug that increases norepinephrine levels by blocking the norepinephrine transporter (NET) is best classified as:
- MAO inhibitor
- NET inhibitor / reuptake inhibitor
- COMT substrate causing rapid inactivation
- Alpha-2 receptor agonist
Correct Answer: NET inhibitor / reuptake inhibitor
Q19. Which topical sympathomimetic is used for glaucoma by reducing aqueous humor production via alpha-2 agonism?
- Timolol
- Brimonidine
- Phenylephrine nasal spray
- Salmeterol eye drops
Correct Answer: Brimonidine
Q20. Tachyphylaxis to nasal decongestants such as oxymetazoline occurs primarily due to:
- Systemic accumulation and toxicity
- Rebound vasodilation from receptor downregulation and local changes
- Allergic hypersensitivity developing within hours
- COMT-mediated conversion to inactive metabolites in the nasal mucosa
Correct Answer: Rebound vasodilation from receptor downregulation and local changes
Q21. Which receptor subtype mediates increased glycogenolysis and gluconeogenesis leading to hyperglycemia after sympathomimetic use?
- Alpha-1
- Beta-1
- Beta-2
- Alpha-2
Correct Answer: Beta-2
Q22. Which drug is a nonselective beta agonist used historically for bradyarrhythmias due to its strong chronotropic effects?
- Isoproterenol
- Phenylephrine
- Clonidine
- Dopamine at low dose
Correct Answer: Isoproterenol
Q23. Which statement about reuptake mechanisms of catecholamines is true?
- Uptake-1 (neuronal) is high capacity and nonspecific
- Uptake-2 (extraneuronal) primarily involves NET in presynaptic terminals
- Uptake-1 (neuronal) is a rapid, high-affinity mechanism inhibited by cocaine and tricyclic antidepressants
- There is no extraneuronal uptake of catecholamines in peripheral tissues
Correct Answer: Uptake-1 (neuronal) is a rapid, high-affinity mechanism inhibited by cocaine and tricyclic antidepressants
Q24. Which clinical scenario best indicates use of a selective beta-1 agonist like dobutamine?
- Acute bronchospasm in asthma
- Cardiogenic shock with decreased cardiac output and adequate blood pressure
- Severe hypotension due to septic vasodilation requiring strong vasoconstriction
- Chronic nasal congestion
Correct Answer: Cardiogenic shock with decreased cardiac output and adequate blood pressure
Q25. Which adverse effect is most likely when combining a sympathomimetic with a nonselective MAOI?
- Severe hypotension and syncope
- Hypertensive crisis with marked increase in blood pressure
- Profound bradycardia and heart block
- Life-threatening hyperkalemia
Correct Answer: Hypertensive crisis with marked increase in blood pressure
Q26. Which drug is a highly selective beta-2 agonist with a long duration used in maintenance therapy for asthma?
- Albuterol (salbutamol)
- Salmeterol
- Dobutamine
- Phenylephrine
Correct Answer: Salmeterol
Q27. The increase in myocardial oxygen demand with beta-1 agonists is primarily due to:
- Peripheral vasodilation reducing afterload
- Increased heart rate and contractility raising cardiac workload
- Direct coronary vasoconstriction via alpha-1 receptors
- Renal sodium retention causing volume overload
Correct Answer: Increased heart rate and contractility raising cardiac workload
Q28. Which enzyme deficiency or inhibition would prolong the action of a catecholamine given intravenously?
- Inhibition of acetylcholinesterase
- Inhibition of monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT)
- Overexpression of P-glycoprotein in the gut
- Increased alcohol dehydrogenase activity
Correct Answer: Inhibition of monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT)
Q29. Which sympathomimetic agent is commonly misused as a stimulant and acts largely via central norepinephrine and dopamine release?
- Pseudoephedrine
- Methylphenidate / Amphetamine
- Phenylephrine
- Mirabegron
Correct Answer: Methylphenidate / Amphetamine
Q30. For a patient with benign prostatic hyperplasia experiencing urinary retention, which sympathomimetic would likely worsen symptoms due to alpha-1 mediated sphincter contraction?
- Prazosin (alpha-1 blocker)
- Tamsulosin (alpha-1A selective blocker)
- Pseudoephedrine or phenylephrine (alpha-1 agonists)
- Mirabegron (beta-3 agonist)
Correct Answer: Pseudoephedrine or phenylephrine (alpha-1 agonists)
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