Alpha adrenergic blockers – Prazosin MCQs With Answer
Prazosin is a prototypical alpha-1 adrenergic blocker widely covered in B. Pharm pharmacology. This concise, Student-friendly post explains prazosin’s mechanism of action as an alpha-1 antagonist, clinical uses in hypertension, benign prostatic hyperplasia symptoms and PTSD-related nightmares, pharmacokinetics (oral bioavailability, hepatic metabolism), common adverse effects such as orthostatic hypotension and reflex tachycardia, and important drug interactions. These 50 targeted MCQs emphasise receptor selectivity, dosing principles, monitoring, and therapeutic comparisons to help B.Pharm students master both theoretical and practical aspects of prazosin therapy. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which receptor subtype does prazosin primarily block to lower blood pressure?
- Beta-1 adrenergic receptor
- Alpha-2 adrenergic receptor
- Alpha-1 adrenergic receptor
- Muscarinic M2 receptor
Correct Answer: Alpha-1 adrenergic receptor
Q2. The main hemodynamic effect of prazosin is:
- Increased cardiac contractility
- Venous and arterial vasodilation reducing preload and afterload
- Direct heart rate reduction by SA node inhibition
- Increased systemic vascular resistance
Correct Answer: Venous and arterial vasodilation reducing preload and afterload
Q3. A common initial adverse effect of prazosin requiring caution at first dose is:
- Dry cough
- First-dose orthostatic hypotension
- Hyperglycemia
- QT prolongation
Correct Answer: First-dose orthostatic hypotension
Q4. Prazosin is most selective for which vascular receptor subtype associated with prostate smooth muscle?
- Alpha-1A subtype
- Alpha-2A subtype
- Beta-2 subtype
- M3 muscarinic subtype
Correct Answer: Alpha-1A subtype
Q5. Prazosin’s oral bioavailability is reduced primarily due to:
- Renal excretion before absorption
- First-pass hepatic metabolism
- Poor intestinal absorption from capsules
- Binding to dietary calcium
Correct Answer: First-pass hepatic metabolism
Q6. Which clinical indication is prazosin commonly used for besides hypertension?
- Type 2 diabetes mellitus
- Post-traumatic stress disorder nightmares
- Asthma exacerbations
- Hyperthyroidism
Correct Answer: Post-traumatic stress disorder nightmares
Q7. Compared with nonselective alpha blockers, prazosin’s selectivity leads to:
- Greater alpha-2 mediated reflex tachycardia
- Less inhibition of presynaptic alpha-2 receptors and fewer sympathetic reflexes
- Complete blockade of beta receptors
- Increased bronchoconstriction risk
Correct Answer: Less inhibition of presynaptic alpha-2 receptors and fewer sympathetic reflexes
Q8. The recommended strategy to reduce first-dose hypotension with prazosin is:
- Administer a large morning dose on an empty stomach
- Start with low dose at bedtime and titrate slowly
- Give it with a beta blocker to blunt effects
- Use IV infusion only
Correct Answer: Start with low dose at bedtime and titrate slowly
Q9. Which pharmacokinetic parameter best describes how long prazosin exerts clinically useful effect per dose?
- Bioavailability
- Volume of distribution
- Plasma half-life
- Cmax only
Correct Answer: Plasma half-life
Q10. Prazosin is metabolized primarily by which organ system?
- Renal tubules via glomerular filtration
- Hepatic microsomal enzymes
- Pulmonary metabolism
- Pancreatic enzymes
Correct Answer: Hepatic microsomal enzymes
Q11. Which adverse effect is most attributable to alpha-1 blockade by prazosin?
- Constipation
- Orthostatic dizziness
- Bradycardia
- Mydriasis
Correct Answer: Orthostatic dizziness
Q12. Combining prazosin with a phosphodiesterase-5 inhibitor (e.g., sildenafil) increases risk of:
- Severe hypertension
- Excessive hypotension and syncope
- Hyperkalemia
- Bronchospasm
Correct Answer: Excessive hypotension and syncope
Q13. Which study point makes prazosin useful in benign prostatic hyperplasia (BPH) symptoms?
- Alpha-1 blockade relaxes prostatic and bladder neck smooth muscle
- It reduces testosterone synthesis in the testes
- It increases bladder contraction strength
- It shrinks the prostate gland size acutely
Correct Answer: Alpha-1 blockade relaxes prostatic and bladder neck smooth muscle
Q14. Prazosin’s effect on heart rate is usually:
- Marked bradycardia due to SA node blockade
- Reflex tachycardia secondary to vasodilation
- Complete AV block in therapeutic doses
- Unchanged in all patients
Correct Answer: Reflex tachycardia secondary to vasodilation
Q15. Which laboratory or monitoring parameter is most relevant when initiating prazosin therapy?
- Serum potassium level
- Orthostatic blood pressure and pulse monitoring
- Serum creatine kinase
- Thyroid function tests
Correct Answer: Orthostatic blood pressure and pulse monitoring
Q16. The term “first-dose phenomenon” with prazosin refers to:
- An allergic rash after first ingestion
- A severe postural hypotension occurring after the initial dose
- Initial headache that persists for weeks
- Transient hyperglycemia on day one
Correct Answer: A severe postural hypotension occurring after the initial dose
Q17. Which of the following is a pharmacologic difference between prazosin and tamsulosin?
- Prazosin is alpha-1 selective; tamsulosin is alpha-2 selective
- Tamsulosin is more selective for alpha-1A subtype found in prostate, prazosin is less subtype-selective
- Prazosin is used exclusively for BPH, tamsulosin for hypertension
- Tamsulosin causes marked systemic hypotension compared to prazosin
Correct Answer: Tamsulosin is more selective for alpha-1A subtype found in prostate, prazosin is less subtype-selective
Q18. Which statement about prazosin’s elimination is correct?
- Primarily excreted unchanged in urine
- Extensively metabolized in liver with both biliary and renal excretion of metabolites
- Cleared mostly by the lungs
- Eliminated by sweat glands
Correct Answer: Extensively metabolized in liver with both biliary and renal excretion of metabolites
Q19. Which adverse effect should be counselled to patients starting prazosin at home?
- Expect pronounced sedation and need to avoid driving permanently
- Stand up slowly to avoid dizziness and fainting
- Frequent urination due to diuretic effect
- Excessive sweating as the main side effect
Correct Answer: Stand up slowly to avoid dizziness and fainting
Q20. Which mechanism explains prazosin’s benefit in reducing symptoms of PTSD nightmares?
- Central blockade of alpha-1 receptors reduces heightened noradrenergic activity during sleep
- It increases cortisol secretion to calm sleep patterns
- It acts as a benzodiazepine receptor agonist
- It elevates histamine levels to induce sedation
Correct Answer: Central blockade of alpha-1 receptors reduces heightened noradrenergic activity during sleep
Q21. A patient on prazosin with erectile dysfunction should be advised that:
- Erectile dysfunction is a common and irreversible side effect
- Prazosin commonly improves sexual function due to increased blood flow
- Some patients may experience priapism requiring urgent care
- Prazosin has no vascular effects relevant to erection
Correct Answer: Some patients may experience priapism requiring urgent care
Q22. Prazosin interacts with which antihypertensive class to increase risk of hypotension?
- Thiazide diuretics only
- ACE inhibitors and nitrates due to additive vasodilation
- Statins due to CYP inhibition
- Calcium supplements
Correct Answer: ACE inhibitors and nitrates due to additive vasodilation
Q23. Which pharmacodynamic effect is expected when prazosin is added to a patient taking a beta blocker?
- Less orthostatic hypotension due to opposing mechanisms
- Potentially increased risk of bradycardia and hypotension due to combined effects
- Complete antagonism and no hemodynamic change
- Increased bronchospasm due to beta blockade reversal
Correct Answer: Potentially increased risk of bradycardia and hypotension due to combined effects
Q24. The onset of action of oral prazosin is typically:
- Within minutes after ingestion
- Within 1–2 hours
- After several days of continuous use only
- After hepatic induction over weeks
Correct Answer: Within 1–2 hours
Q25. Which of the following is TRUE regarding prazosin dosing in elderly patients?
- Elderly patients tolerate standard adult doses without adjustment
- Start at lower doses and titrate slowly due to increased orthostatic risk
- Should never be used in patients over 65 years
- Require simultaneous diuretic initiation to be effective
Correct Answer: Start at lower doses and titrate slowly due to increased orthostatic risk
Q26. Which formulation factor influences prazosin’s clinical use?
- It is available as long-acting injectable only
- Immediate-release oral tablets with relatively short half-life require multiple daily dosing
- Topical use is standard for hypertension
- It is given as an inhaled aerosol for rapid control
Correct Answer: Immediate-release oral tablets with relatively short half-life require multiple daily dosing
Q27. Which sign would most likely indicate an overdose of prazosin?
- Severe hypertension and tachypnea
- Profound hypotension and syncope
- Marked hyperreflexia
- Acute urinary retention
Correct Answer: Profound hypotension and syncope
Q28. Which statement about prazosin and pregnancy is correct?
- Prazosin is a proven teratogen and absolutely contraindicated in pregnancy
- It should be used with caution; categorized as pregnancy category C in many references
- It is the first-line antihypertensive in pregnancy
- It is excreted in breast milk and banned in lactation
Correct Answer: It should be used with caution; categorized as pregnancy category C in many references
Q29. Which laboratory abnormality is a known, common direct effect of prazosin use?
- Elevated liver enzymes in all users
- No consistent direct effect on routine serum electrolytes
- Marked neutropenia
- Severe hyperkalemia
Correct Answer: No consistent direct effect on routine serum electrolytes
Q30. In a hypertensive emergency, prazosin is:
- First-line IV agent for immediate BP control
- Not typically used due to short half-life and oral route preference
- Preferred because it causes rapid reflex bradycardia
- Contraindicated in all BP emergencies
Correct Answer: Not typically used due to short half-life and oral route preference
Q31. Which structural or chemical property of prazosin contributes to its central nervous system (CNS) effects?
- High molecular weight preventing BBB penetration
- Moderate lipophilicity allowing some central alpha-1 blockade
- It is a peptide that is degraded before CNS entry
- Only IV forms cross the BBB
Correct Answer: Moderate lipophilicity allowing some central alpha-1 blockade
Q32. How does chronic use of prazosin affect peripheral resistance long-term?
- Peripheral resistance increases due to receptor upregulation
- Peripheral resistance is persistently reduced, lowering blood pressure
- No change in peripheral resistance after initial dose
- Peripheral resistance fluctuates unpredictably
Correct Answer: Peripheral resistance is persistently reduced, lowering blood pressure
Q33. Which dosing advice is appropriate for a patient who missed a dose of prazosin?
- Take double the next dose to compensate
- Skip the missed dose and take the next scheduled dose; avoid doubling
- Stop therapy permanently
- Take the missed dose plus an extra once daily
Correct Answer: Skip the missed dose and take the next scheduled dose; avoid doubling
Q34. Which symptom might indicate prazosin-induced nasal congestion?
- Decreased nasal airflow due to vasodilation of nasal mucosa
- Loss of smell only
- Nasal bleeding due to platelet dysfunction
- Dry, crusted nasal mucosa exclusively
Correct Answer: Decreased nasal airflow due to vasodilation of nasal mucosa
Q35. For B. Pharm students, which pharmacology concept best explains prazosin’s action?
- Agonism at Gs-coupled beta receptors
- Competitive antagonism at post-synaptic alpha-1 adrenergic receptors
- Irreversible blockade of muscarinic receptors
- Inhibition of acetylcholinesterase
Correct Answer: Competitive antagonism at post-synaptic alpha-1 adrenergic receptors
Q36. Prazosin’s clinical antihypertensive effect is most closely related to which downstream event?
- Increased intracellular cAMP in vascular smooth muscle
- Reduced smooth muscle contraction via decreased IP3-mediated calcium release
- Activation of sodium channels in smooth muscle
- Enhanced release of norepinephrine
Correct Answer: Reduced smooth muscle contraction via decreased IP3-mediated calcium release
Q37. Which patient history would prompt caution before starting prazosin?
- History of stable migraines only
- History of frequent orthostatic fainting spells
- Well-controlled hypothyroidism on levothyroxine
- Seasonal allergic rhinitis
Correct Answer: History of frequent orthostatic fainting spells
Q38. Which adverse effect is more commonly observed with higher doses of prazosin?
- Hyperactivity and insomnia
- Worsening orthostatic hypotension and syncope
- Hair growth stimulation
- Hypercalcemia
Correct Answer: Worsening orthostatic hypotension and syncope
Q39. Which monitoring is most appropriate for titrating prazosin dose in hypertension?
- Ambulatory blood pressure monitoring and orthostatic vitals
- Daily serum transaminase measurement
- Weekly complete blood count
- Daily fasting blood glucose checks
Correct Answer: Ambulatory blood pressure monitoring and orthostatic vitals
Q40. Prazosin’s effect on urinary flow in BPH is primarily due to:
- Reduction in prostate size within 24 hours
- Relaxation of smooth muscle at bladder neck improving urinary flow
- Diuretic-induced increased urine volume
- Inhibition of detrusor muscle contraction
Correct Answer: Relaxation of smooth muscle at bladder neck improving urinary flow
Q41. An advantage of selective alpha-1 blockers like prazosin over nonselective alpha blockers is:
- Complete prevention of reflex tachycardia
- Lower incidence of centrally mediated side effects and less severe reflex sympathetic activation
- They increase adrenergic neurotransmission
- They cause more sedation
Correct Answer: Lower incidence of centrally mediated side effects and less severe reflex sympathetic activation
Q42. Which statement correctly describes prazosin’s interaction with alcohol?
- Alcohol antagonizes prazosin’s BP-lowering effects
- Concurrent alcohol use may potentiate hypotension and dizziness
- Alcohol prevents prazosin absorption in the gut
- Alcohol converts prazosin into an inactive metabolite
Correct Answer: Concurrent alcohol use may potentiate hypotension and dizziness
Q43. Which therapeutic effect is least likely with prazosin use?
- Reduction in peripheral vascular resistance
- Improvement in nocturnal PTSD nightmares
- Rapid reduction of intracranial pressure
- Symptom improvement in lower urinary tract obstruction
Correct Answer: Rapid reduction of intracranial pressure
Q44. Which statement about prazosin dosing frequency is correct?
- Once-weekly dosing is sufficient due to depot effect
- Multiple daily dosing may be required because of relatively short duration of action
- Single dose cures hypertension permanently
- Dosing frequency is irrelevant to clinical effect
Correct Answer: Multiple daily dosing may be required because of relatively short duration of action
Q45. In a patient with liver impairment, prazosin dosage should be:
- Increased due to reduced effect
- Reduced and titrated carefully because of decreased metabolism
- Stopped completely as it is nephrotoxic
- Unchanged irrespective of hepatic function
Correct Answer: Reduced and titrated carefully because of decreased metabolism
Q46. Which teaching point is most important when advising a patient starting nighttime prazosin?
- Take the initial dose at bedtime to reduce symptomatic hypotension risk
- Always take with a heavy meal to increase absorption
- Avoid drinking fluids before bed to prevent nocturia
- Expect immediate muscle weakness on standing
Correct Answer: Take the initial dose at bedtime to reduce symptomatic hypotension risk
Q47. Which receptor location is primarily responsible for prazosin’s antihypertensive action?
- Cardiac beta-1 receptors in ventricles
- Vascular smooth muscle alpha-1 receptors
- Central alpha-2 receptors in brainstem
- Renal dopamine receptors
Correct Answer: Vascular smooth muscle alpha-1 receptors
Q48. Which adverse effect of prazosin requires immediate medical attention?
- Mild dizziness on standing that improves
- Severe fainting or recurrent syncope
- Transient nasal stuffiness
- Occasional headache after dose increase
Correct Answer: Severe fainting or recurrent syncope
Q49. When comparing potency and duration, prazosin is best described as:
- Very long-acting and highly potent alpha-1 blocker taken once weekly
- Moderate potency with relatively short half-life requiring repeated dosing
- Nonselective beta blocker mistakenly classified as alpha blocker
- Purely topical agent with local action only
Correct Answer: Moderate potency with relatively short half-life requiring repeated dosing
Q50. Which counselling point is appropriate about driving after starting prazosin?
- Driving is always safe immediately after the first dose
- Avoid driving until you know how prazosin affects you due to possible dizziness
- Prazosin causes increased alertness, so driving is improved
- Only nighttime driving is risky; daytime driving is always safe
Correct Answer: Avoid driving until you know how prazosin affects you due to possible dizziness
