Direct acting sympathomimetics – Isoproterenol MCQs With Answer

Direct acting sympathomimetics – Isoproterenol MCQs With Answer: This concise, SEO-friendly introduction helps B. Pharm students master pharmacology of direct-acting sympathomimetics with a focus on isoproterenol. Learn core concepts such as mechanism of action as a non-selective beta-adrenergic agonist, receptor selectivity (β1/β2), intracellular cAMP signaling, pharmacokinetics (COMT/MAO metabolism, short half-life), clinical uses, adverse effects, drug interactions and contraindications. These targeted MCQs emphasize therapeutic implications, dosing principles, and distinctions from other catecholamines to build exam-ready knowledge. Clear explanations strengthen understanding of pharmacodynamics, safety considerations and clinical scenarios. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which receptor profile best describes isoproterenol?

• Selective β1 agonist
• Selective β2 agonist
• Non-selective β1 and β2 agonist
• α and β agonist with greater α activity

Correct Answer: Non-selective β1 and β2 agonist

Q2. The primary intracellular mediator increased by isoproterenol activation of β receptors is:

• cGMP
• cAMP
• IP3
• DAG

Correct Answer: cAMP

Q3. Which enzyme is mainly responsible for metabolism of isoproterenol?

• Cytochrome P450 3A4
• Monoamine oxidase (MAO)
• Catechol-O-methyltransferase (COMT)
• Butyrylcholinesterase

Correct Answer: Catechol-O-methyltransferase (COMT)

Q4. Clinically, isoproterenol is most appropriately used for:

• Treatment of anaphylactic shock as first-line agent
• Acute severe bradycardia and heart block (temporary therapy)
• Long-term management of hypertension
• Routine outpatient asthma maintenance

Correct Answer: Acute severe bradycardia and heart block (temporary therapy)

Q5. Which cardiovascular effect is characteristic of isoproterenol?

• Increased peripheral resistance with decreased heart rate
• Decreased cardiac output and increased diastolic BP
• Increased heart rate and decreased peripheral resistance
• Marked α-mediated vasoconstriction raising mean arterial pressure

Correct Answer: Increased heart rate and decreased peripheral resistance

Q6. Isoproterenol’s bronchodilator effect is primarily mediated through:

• β1 receptor activation in bronchial smooth muscle
• β2 receptor activation increasing cAMP in bronchial smooth muscle
• α1 receptor-mediated bronchodilation
• Muscarinic receptor antagonism

Correct Answer: β2 receptor activation increasing cAMP in bronchial smooth muscle

Q7. A common metabolic side effect of β2 stimulation by isoproterenol is:

• Hyperkalemia due to extracellular K+ release
• Hypoglycemia from increased insulin sensitivity
• Hypokalemia due to cellular shift of potassium
• Hyponatremia from ADH release

Correct Answer: Hypokalemia due to cellular shift of potassium

Q8. Which statement about isoproterenol’s effect on blood pressure is correct?

• It uniformly raises both systolic and diastolic blood pressure
• It increases systolic pressure while decreasing diastolic pressure, often lowering mean arterial pressure
• It causes marked α-mediated diastolic hypertension
• It has no effect on vascular tone

Correct Answer: It increases systolic pressure while decreasing diastolic pressure, often lowering mean arterial pressure

Q9. Isoproterenol’s chronotropic effect is mainly due to β1 stimulation at which site?

• Vascular smooth muscle
• Sinoatrial (SA) node
• Respiratory epithelium
• Adrenal medulla

Correct Answer: Sinoatrial (SA) node

Q10. Which adverse effect is most likely with IV isoproterenol in patients with coronary artery disease?

• Improved myocardial oxygen balance
• Precipitation of angina due to increased heart rate and myocardial oxygen demand
• Reduced myocardial contractility causing heart failure
• Reduced heart rate causing bradycardia

Correct Answer: Precipitation of angina due to increased heart rate and myocardial oxygen demand

Q11. Which pharmacological property explains tachyphylaxis to repeated isoproterenol doses?

• Upregulation of β receptors
• Receptor phosphorylation and β-arrestin mediated desensitization
• Inhibition of COMT making drug more active
• Activation of muscarinic receptors counteracting effect

Correct Answer: Receptor phosphorylation and β-arrestin mediated desensitization

Q12. Compared with epinephrine, isoproterenol has:

• Greater α activity and less β activity
• Similar α and stronger β1 activity
• No α activity and predominantly β activity
• Only peripheral α activity

Correct Answer: No α activity and predominantly β activity

Q13. Which drug interaction increases the risk of exaggerated tachycardia when combined with isoproterenol?

• Non-selective β-blockers
• MAO inhibitors (MAOIs)
• Digitalis glycosides
• Calcium channel blockers

Correct Answer: MAO inhibitors (MAOIs)

Q14. The most appropriate route for emergency use of isoproterenol is:

• Oral tablet
• Intravenous infusion or bolus
• Topical skin application
• Long-term intramuscular depot

Correct Answer: Intravenous infusion or bolus

Q15. In pharmacokinetics, isoproterenol’s short duration of action is mainly due to:

• Rapid renal excretion unchanged
• Extensive hepatic CYP450 metabolism
• Rapid enzymatic breakdown by COMT and MAO
• Slow absorption from GI tract

Correct Answer: Rapid enzymatic breakdown by COMT and MAO

Q16. Which electrocardiographic effect may occur with isoproterenol administration?

• Marked PR prolongation and bradycardia
• Shortened PR interval and increased heart rate with possible arrhythmias
• ST segment elevation identical to MI
• No effect on cardiac rhythm

Correct Answer: Shortened PR interval and increased heart rate with possible arrhythmias

Q17. Isoproterenol promotes glycogenolysis primarily through which receptor action?

• β1 receptor on hepatocytes
• β2 receptor on hepatocytes
• α2 receptor on pancreas
• Muscarinic receptors on liver

Correct Answer: β2 receptor on hepatocytes

Q18. Which patient condition is a relative contraindication to isoproterenol?

• Complete heart block requiring pacing (unless pacing unavailable)
• Asthma with bronchospasm
• Severe hypotension with need for vasoconstriction
• Bradycardia due to AV block where pacing is available

Correct Answer: Severe hypotension with need for vasoconstriction

Q19. Which of the following best describes isoproterenol’s effect on renal blood flow?

• Decreases renal blood flow via α1 vasoconstriction
• Increases renal blood flow due to systemic vasodilation
• No effect on renal circulation
• Causes renal artery reflex spasm

Correct Answer: Increases renal blood flow due to systemic vasodilation

Q20. When comparing isoproterenol with dobutamine, which is true?

• Isoproterenol is more β2-selective and causes more vasodilation than dobutamine
• Dobutamine is non-selective β agonist like isoproterenol
• Isoproterenol is α1 selective compared to dobutamine
• Both have identical receptor profiles

Correct Answer: Isoproterenol is more β2-selective and causes more vasodilation than dobutamine

Q21. A biochemical consequence of β receptor activation by isoproterenol in cardiac myocytes is:

• Decreased intracellular cAMP and reduced contractility
• Increased cAMP leading to enhanced Ca2+ influx and positive inotropy
• Activation of phospholipase C increasing IP3/DAG only
• Direct opening of K+ channels causing hyperpolarization

Correct Answer: Increased cAMP leading to enhanced Ca2+ influx and positive inotropy

Q22. Which monitoring parameter is most critical during IV isoproterenol infusion?

• Serum cholesterol
• ECG and heart rate
• Liver function tests
• Visual acuity

Correct Answer: ECG and heart rate

Q23. Which statement about isoproterenol and insulin is correct?

• β2 stimulation by isoproterenol consistently causes hypoglycemia by increasing insulin sensitivity
• β2 stimulation can increase glycogenolysis and may raise blood glucose
• Isoproterenol is a direct insulin secretagogue via α receptors
• It has no metabolic effects

Correct Answer: β2 stimulation can increase glycogenolysis and may raise blood glucose

Q24. Which adverse effect is least likely with therapeutic doses of isoproterenol?

• Tachycardia and palpitations
• Bronchoconstriction
• Headache and flushing from vasodilation
• Arrhythmias

Correct Answer: Bronchoconstriction

Q25. In heart block management, isoproterenol is used because it:

• Blocks AV node conduction
• Increases AV nodal conduction and heart rate
• Causes long-term rhythm control
• Is a sedative that reduces ectopy

Correct Answer: Increases AV nodal conduction and heart rate

Q26. Which physiological reflex may be observed after isoproterenol-induced vasodilation?

• Baroreceptor-mediated reflex bradycardia
• Baroreceptor-mediated reflex tachycardia
• Increased parasympathetic outflow causing hypotension
• No reflex changes

Correct Answer: Baroreceptor-mediated reflex tachycardia

Q27. Which structural feature classically makes a sympathomimetic susceptible to COMT metabolism?

• Tertiary amine group
• Catechol (adjacent dihydroxy) moiety on the aromatic ring
• Long alkyl tail
• Ether linkage

Correct Answer: Catechol (adjacent dihydroxy) moiety on the aromatic ring

Q28. Isoproterenol administration in hyperthyroid patients can cause:

• Reduced sensitivity to catecholamines
• Exaggerated tachycardia due to upregulated β receptors
• No change in cardiovascular response
• Marked α blockade

Correct Answer: Exaggerated tachycardia due to upregulated β receptors

Q29. Which laboratory change can result from β2 stimulation by isoproterenol?

• Hyperkalemia due to K+ efflux from cells
• Increased serum lactate from enhanced glycolysis
• Decreased blood glucose due to increased insulin only
• Marked rise in serum creatinine

Correct Answer: Increased serum lactate from enhanced glycolysis

Q30. Which is a pharmacodynamic difference between intravenous isoproterenol and inhaled β2 agonists?

• Isoproterenol given IV has systemic β1 and β2 effects; inhaled β2 agonists act mainly in the lung with less systemic β1 effect
• IV isoproterenol is selective for β2 only
• Inhaled β2 agonists have more cardiac β1 activity than IV isoproterenol
• Both routes produce identical systemic effects

Correct Answer: Isoproterenol given IV has systemic β1 and β2 effects; inhaled β2 agonists act mainly in the lung with less systemic β1 effect

Q31. Which drug would antagonize the cardiovascular effects of isoproterenol?

• Propranolol (a non-selective β-blocker)
• Salbutamol (a β2 agonist)
• Phenylephrine (an α1 agonist)
• Isosorbide dinitrate (a nitrate)

Correct Answer: Propranolol (a non-selective β-blocker)

Q32. Isoproterenol’s effect on glycogen in skeletal muscle is primarily:

• Inhibition of glycogenolysis via β blockade
• Stimulation of glycogenolysis via β2 receptors
• Direct glycogen synthesis via α receptors
• No effect on muscle glycogen

Correct Answer: Stimulation of glycogenolysis via β2 receptors

Q33. Which adverse effect necessitates caution when using isoproterenol in patients on tricyclic antidepressants (TCAs)?

• Blunted hemodynamic response due to increased COMT activity
• Exaggerated cardiovascular stimulation and arrhythmias due to increased catecholamine sensitivity
• Direct neutralization of isoproterenol by TCAs
• No interaction exists

Correct Answer: Exaggerated cardiovascular stimulation and arrhythmias due to increased catecholamine sensitivity

Q34. Which receptor-mediated effect explains bronchodilation but limits use of isoproterenol in asthma?

• Strong α1-mediated bronchoconstriction
• Powerful β2 bronchodilation but significant β1 cardiac stimulation causing tachycardia
• Prominent anti-inflammatory action making it ideal for chronic therapy
• Irreversible receptor activation

Correct Answer: Powerful β2 bronchodilation but significant β1 cardiac stimulation causing tachycardia

Q35. Which physiological change is expected after isoproterenol administration during a hypotensive crisis?

• Marked increase in diastolic pressure via α1 stimulation
• Possible fall in mean arterial pressure due to β2-mediated vasodilation despite increased cardiac output
• Complete correction of hypotension in all cases
• Profound renal vasoconstriction reducing urine output

Correct Answer: Possible fall in mean arterial pressure due to β2-mediated vasodilation despite increased cardiac output

Q36. Which signaling protein directly couples β-adrenergic receptors to increased cAMP?

• Gq protein activating PLC
• Gi protein inhibiting adenylate cyclase
• Gs protein stimulating adenylate cyclase
• Tyrosine kinase receptor activation

Correct Answer: Gs protein stimulating adenylate cyclase

Q37. In overdose, isoproterenol toxicity most likely presents with:

• Severe bradycardia and hypotension without arrhythmia
• Severe tachycardia, arrhythmias, myocardial ischemia and hypotension
• Profound sedation and respiratory depression
• Marked renal failure as earliest sign

Correct Answer: Severe tachycardia, arrhythmias, myocardial ischemia and hypotension

Q38. Which laboratory test could be affected by isoproterenol administration and should be monitored in critical patients?

• Liver transaminases only
• Serum potassium due to β2-mediated shift into cells
• Hemoglobin exclusively
• Serum amylase only

Correct Answer: Serum potassium due to β2-mediated shift into cells

Q39. Which of the following best classifies isoproterenol pharmacologically?

• Indirect-acting sympathomimetic
• Direct-acting sympathomimetic
• Cholinergic agonist
• Alpha-adrenergic antagonist

Correct Answer: Direct-acting sympathomimetic

Q40. In experimental pharmacology, isoproterenol is frequently used to:

• Induce hypertension in animal models
• Induce myocardial ischemia and heart failure-like injury at high doses
• Block β receptors in receptor studies
• Serve as a specific α2 agonist

Correct Answer: Induce myocardial ischemia and heart failure-like injury at high doses

Q41. Which clinical monitoring is essential when isoproterenol is used to treat bradyarrhythmias?

• Serum cholesterol levels
• Continuous ECG and blood pressure monitoring
• Pulmonary function testing every hour
• Daily liver enzyme tests

Correct Answer: Continuous ECG and blood pressure monitoring

Q42. Which effect of isoproterenol on peripheral vascular resistance is expected?

• Increase due to α1 activation
• Decrease due to β2-mediated vasodilation
• No change because it only affects heart
• Initial increase then sustained increase only

Correct Answer: Decrease due to β2-mediated vasodilation

Q43. Which scenario increases the risk of arrhythmias with isoproterenol?

• Concurrent use of β-blockers
• Hypokalemia and myocardial ischemia
• Normal potassium and absence of ischemia
• Low-dose inhaled administration only

Correct Answer: Hypokalemia and myocardial ischemia

Q44. For exam-focused pharmacology: the therapeutic index of isoproterenol is considered:

• Very wide and safe for all outpatient use
• Narrower due to risk of cardiac adverse effects and arrhythmias
• Irrelevant because it is not absorbed
• Infinite as there is no toxicity

Correct Answer: Narrower due to risk of cardiac adverse effects and arrhythmias

Q45. Which receptor adaptation occurs with chronic β agonist exposure like isoproterenol?

• Increased receptor density (upregulation)
• Receptor internalization and downregulation
• Complete conversion to α receptors
• No change in receptor number or function

Correct Answer: Receptor internalization and downregulation

Q46. Which adjunctive therapy might be used to counteract severe tachycardia caused by isoproterenol?

• Increase isoproterenol dose
• Administer a short-acting β-blocker carefully under monitoring
• Give high-dose epinephrine
• Start long-term oral theophylline

Correct Answer: Administer a short-acting β-blocker carefully under monitoring

Q47. Which statement about isoproterenol and pregnancy is most appropriate for B. Pharm students?

• It is completely safe and recommended during pregnancy without restriction
• Use with caution; weigh maternal benefits against fetal risks and monitor closely
• Contraindicated in all trimesters irrespective of indication
• Causes teratogenesis in all animal studies

Correct Answer: Use with caution; weigh maternal benefits against fetal risks and monitor closely

Q48. Which laboratory enzyme activity would reduce isoproterenol effectiveness if inhibited?

• COMT inhibition increases breakdown of isoproterenol
• MAO inhibition alone prevents isoproterenol inactivation completely
• COMT inhibition would prolong isoproterenol action by preventing one metabolic pathway
• Inhibition of acetylcholinesterase directly inactivates isoproterenol

Correct Answer: COMT inhibition would prolong isoproterenol action by preventing one metabolic pathway

Q49. Which clinical comparison is correct regarding isoproterenol and norepinephrine?

• Isoproterenol has strong α1 effects leading to vasoconstriction like norepinephrine
• Norepinephrine predominantly increases peripheral resistance via α1, while isoproterenol causes vasodilation via β2
• Both drugs have identical pressor profiles
• Neither affects heart rate or contractility

Correct Answer: Norepinephrine predominantly increases peripheral resistance via α1, while isoproterenol causes vasodilation via β2

Q50. For MCQ practice: the most accurate exam-style statement about isoproterenol is:

• It is an indirect sympathomimetic that releases norepinephrine
• It is a direct β agonist with clinical uses limited by cardiac side effects
• It is the preferred long-term oral agent for asthma
• It selectively activates α2 receptors to lower blood pressure

Correct Answer: It is a direct β agonist with clinical uses limited by cardiac side effects

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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