Pharmacology of antidiuretics explores drugs that mimic or block antidiuretic hormone (ADH/vasopressin) action—key for water balance, plasma osmolality, and blood pressure regulation. This concise guide for B. Pharm students covers mechanisms (V1 vs V2 receptors), intracellular signaling (cAMP, aquaporin-2 insertion), major agents (desmopressin, vasopressin, conivaptan, tolvaptan), clinical uses (central diabetes insipidus, von Willebrand disease, SIADH), pharmacokinetics, adverse effects (hyponatremia, vasoconstriction), contraindications, and therapeutic monitoring. Emphasis is on receptor selectivity, drug interactions, dosing routes and management of complications. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which receptor subtype mediates the renal antidiuretic effect of vasopressin?
- V1 receptor
- V2 receptor
- V3 receptor
- Alpha-1 adrenergic receptor
Correct Answer: V2 receptor
Q2. Desmopressin is preferred over vasopressin for treating central diabetes insipidus because it:
- Has stronger V1 vasoconstrictive actions
- Is more selective for V2 receptors with longer duration
- Causes significant platelet aggregation
- Is an antagonist at V2 receptors
Correct Answer: Is more selective for V2 receptors with longer duration
Q3. The primary intracellular second messenger activated by V2 receptor stimulation in collecting duct cells is:
- IP3 and DAG
- cAMP
- cGMP
- Calcium-calmodulin
Correct Answer: cAMP
Q4. Aquaporin-2 channels are inserted into the apical membrane of principal cells in response to:
- V1 receptor-mediated IP3 signaling
- V2 receptor-mediated cAMP and PKA activation
- Angiotensin II binding to AT1 receptors
- Aldosterone-induced gene transcription
Correct Answer: V2 receptor-mediated cAMP and PKA activation
Q5. Which condition is a primary indication for vasopressin V2 receptor antagonists (vaptans)?
- Central diabetes insipidus
- Nephrogenic diabetes insipidus
- Syndrome of inappropriate ADH secretion (SIADH) with hyponatremia
- Hypovolemic hyponatremia
Correct Answer: Syndrome of inappropriate ADH secretion (SIADH) with hyponatremia
Q6. Tolvaptan differs from conivaptan primarily by being:
- Nonselective V1/V2 antagonist
- Selective V2 receptor antagonist administered orally
- An IV-only V2 agonist
- A V3 receptor agonist used for pituitary disorders
Correct Answer: Selective V2 receptor antagonist administered orally
Q7. A major adverse effect of desmopressin therapy is:
- Hypernatremia
- Hyponatremia due to water retention
- Renal vasodilation leading to polyuria
- Profound hypotension
Correct Answer: Hyponatremia due to water retention
Q8. Which laboratory test is most useful to differentiate central DI from primary polydipsia?
- Serum potassium concentration
- Water deprivation test followed by desmopressin administration
- Random blood glucose measurement
- Urine protein electrophoresis
Correct Answer: Water deprivation test followed by desmopressin administration
Q9. Conivaptan’s additional blockade of V1 receptors can lead to which clinical effect?
- Renal water reabsorption increase
- Systemic vasodilation and hypotension
- Enhanced platelet aggregation
- Increased aldosterone secretion
Correct Answer: Systemic vasodilation and hypotension
Q10. In nephrogenic diabetes insipidus, the most appropriate pharmacologic therapy is often:
- High-dose desmopressin
- Thiazide diuretics and low-salt diet
- V2 receptor agonists
- Tolvaptan to block V2 receptors
Correct Answer: Thiazide diuretics and low-salt diet
Q11. Desmopressin is used in hemophilia A and von Willebrand disease because it:
- Directly replaces factor VIII
- Stimulates release of von Willebrand factor and factor VIII from endothelium
- Is an anticoagulant that reduces thrombus formation
- Inhibits platelet aggregation
Correct Answer: Stimulates release of von Willebrand factor and factor VIII from endothelium
Q12. Which drug interaction increases the risk of hyponatremia when combined with desmopressin?
- Loop diuretics
- SSRIs and carbamazepine
- NSAIDs like ibuprofen
- Beta-blockers
Correct Answer: SSRIs and carbamazepine
Q13. The mechanism by which vaptans correct hyponatremia is primarily due to:
- Increased renal sodium retention
- Promotion of free water excretion (aquaresis) without natriuresis
- Enhanced aldosterone release
- Decreased glomerular filtration rate
Correct Answer: Promotion of free water excretion (aquaresis) without natriuresis
Q14. Which adverse effect is most associated with rapid correction of chronic hyponatremia when using vaptans?
- Osmotic demyelination syndrome (central pontine myelinolysis)
- Acute tubular necrosis
- Severe hyperkalemia
- Bronchospasm
Correct Answer: Osmotic demyelination syndrome (central pontine myelinolysis)
Q15. Which statement about vasopressin pharmacokinetics is correct?
- Desmopressin has a shorter half-life than endogenous vasopressin
- Desmopressin has enhanced oral bioavailability compared to IV vasopressin
- Desmopressin is available as intranasal, oral, and parenteral formulations with prolonged action
- Vaptans are peptides rapidly degraded by peptidases
Correct Answer: Desmopressin is available as intranasal, oral, and parenteral formulations with prolonged action
Q16. Which patient scenario is a contraindication to using desmopressin?
- Central diabetes insipidus with hypernatremia
- Syndrome of inappropriate ADH secretion (SIADH)
- Bleeding due to von Willebrand disease
- Nocturnal enuresis in older children
Correct Answer: Syndrome of inappropriate ADH secretion (SIADH)
Q17. Lithium-induced nephrogenic diabetes insipidus results from lithium’s effect to:
- Enhance V2 receptor signaling
- Inhibit adenylate cyclase and impair aquaporin-2 expression in collecting ducts
- Increase ADH secretion from posterior pituitary
- Stimulate aldosterone release leading to sodium retention
Correct Answer: Inhibit adenylate cyclase and impair aquaporin-2 expression in collecting ducts
Q18. Which monitoring parameter is essential after initiating desmopressin therapy?
- Serum creatine kinase
- Serum sodium concentration
- Serum magnesium levels
- Complete blood count only
Correct Answer: Serum sodium concentration
Q19. A selective V1 receptor agonist would most likely cause:
- Increased water reabsorption in kidney
- Systemic vasoconstriction and increased blood pressure
- Promotion of free water excretion
- Stimulation of aldosterone release from adrenal cortex
Correct Answer: Systemic vasoconstriction and increased blood pressure
Q20. Which therapeutic use of vasopressin analogues exploits their V1-mediated vasoconstrictive action?
- Treatment of central diabetes insipidus
- Control of bleeding in esophageal varices or refractory hypotension in septic shock
- Management of SIADH
- Treatment of nephrogenic diabetes insipidus
Correct Answer: Control of bleeding in esophageal varices or refractory hypotension in septic shock
Q21. Which physiological stimuli primarily increase endogenous ADH release?
- Decreased plasma osmolality and increased blood pressure
- Increased plasma osmolality and decreased arterial blood pressure
- High atrial stretch from volume overload
- Elevated GFR
Correct Answer: Increased plasma osmolality and decreased arterial blood pressure
Q22. In SIADH, which characteristic is typically observed?
- Hypernatremia with low urine osmolality
- Hyponatremia with inappropriately concentrated urine
- Polyuria and hypernatremia due to ADH deficiency
- High serum osmolality with dilute urine
Correct Answer: Hyponatremia with inappropriately concentrated urine
Q23. Which statement about the mechanism of action of tolvaptan is correct?
- It is a peptide agonist of V2 receptors
- It competitively antagonizes V2 receptors causing aquaresis
- It stimulates V1 receptors causing vasoconstriction
- It increases aldosterone production to retain sodium
Correct Answer: It competitively antagonizes V2 receptors causing aquaresis
Q24. Which adverse effect is most specifically associated with vaptan therapy besides rapid sodium correction?
- Hepatotoxicity with long-term use (noted with tolvaptan)
- Severe hypokalemia
- Excessive antiplatelet activity
- Thyroid dysfunction
Correct Answer: Hepatotoxicity with long-term use (noted with tolvaptan)
Q25. Which dosing route of desmopressin is commonly used for nocturnal enuresis in children?
- Intravenous infusion
- Intranasal spray or oral tablet at bedtime
- Subcutaneous infusion pump
- Topical application to skin
Correct Answer: Intranasal spray or oral tablet at bedtime
Q26. Why are vaptans contraindicated in patients who are unable to perceive or respond to thirst?
- They cause excessive sodium retention
- They increase risk of rapid hypernatremia
- They may produce rapid water loss causing severe hypernatremia without compensatory intake
- They stimulate ADH release
Correct Answer: They may produce rapid water loss causing severe hypernatremia without compensatory intake
Q27. Which structural feature distinguishes desmopressin from endogenous vasopressin?
- Lack of peptide backbone
- Deamination at position 1 and D-arginine at position 8 increasing V2 selectivity and half-life
- Additional sulfate group enhancing V1 activity
- Conjugation to a lipid moiety for oral absorption
Correct Answer: Deamination at position 1 and D-arginine at position 8 increasing V2 selectivity and half-life
Q28. Which treatment approach is recommended for acute severe hyponatremia due to water intoxication from desmopressin overdose?
- Rapid infusion of hypotonic saline
- Fluid restriction and administration of hypertonic saline carefully with monitoring
- Start oral desmopressin to stabilize levels
- Immediate dialysis without correcting sodium
Correct Answer: Fluid restriction and administration of hypertonic saline carefully with monitoring
Q29. Which monitoring is important when using tolvaptan in hospitalized patients with hyponatremia?
- Daily liver function tests and frequent serum sodium measurements
- Only blood pressure monitoring is required
- No monitoring is necessary for short courses
- Weekly lipid profile
Correct Answer: Daily liver function tests and frequent serum sodium measurements
Q30. Which pharmacologic approach can help partially overcome nephrogenic DI caused by lithium?
- High-dose desmopressin
- Amiloride to reduce lithium entry into collecting duct cells combined with thiazide diuretics
- Loop diuretics alone
- V2 receptor agonists like tolvaptan
Correct Answer: Amiloride to reduce lithium entry into collecting duct cells combined with thiazide diuretics
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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