Histamine and its antagonists MCQs With Answer

Histamine and its antagonists MCQs With Answer

Histamine is a key bioamine in pharmacology controlling allergy, gastric acid secretion and central neurotransmission. B.Pharm students must master histamine receptors (H1, H2, H3, H4), synthesis by L‑histidine decarboxylase, metabolism via diamine oxidase and HNMT, and the pharmacology of H1 and H2 antagonists. This introduction links mechanism of action, therapeutic uses, adverse effects, drug interactions and pharmacokinetics of first‑ and second‑generation antihistamines, H2 blockers and clinical considerations such as QT risk and CYP interactions. Understanding these details is vital for safe prescribing and drug development. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which enzyme catalyzes the synthesis of histamine from L‑histidine?

• L‑histidine decarboxylase
• Histamine N‑methyltransferase
• Diamine oxidase (DAO)
• Monoamine oxidase

Correct Answer: L‑histidine decarboxylase

Q2. Which receptor subtype primarily mediates bronchoconstriction and increased vascular permeability in allergic reactions?

• H1 receptor
• H2 receptor
• H3 receptor
• H4 receptor

Correct Answer: H1 receptor

Q3. Which of the following is a characteristic adverse effect of first‑generation H1 antihistamines?

• Marked sedation due to central nervous system penetration
• Selective inhibition of gastric acid secretion
• Renal tubular necrosis
• Excessive salivation

Correct Answer: Marked sedation due to central nervous system penetration

Q4. Cimetidine inhibits which of the following cytochrome P450 isoenzymes leading to multiple drug interactions?

• CYP3A4, CYP1A2 and CYP2C19
• CYP2E1 only
• CYP4A11 only
• CYP11B2 only

Correct Answer: CYP3A4, CYP1A2 and CYP2C19

Q5. Which H2 antagonist has the least potential for CYP‑mediated drug interactions?

• Famotidine
• Cimetidine
• Nizatidine
• Ranitidine

Correct Answer: Famotidine

Q6. Which antihistamine is an inverse agonist at the H1 receptor rather than a neutral antagonist?

• Loratadine
• Histamine (endogenous ligand)
• Propranolol
• Omeprazole

Correct Answer: Loratadine

Q7. Which metabolic pathway is primarily responsible for degradation of extracellular histamine in the gut and circulation?

• Diamine oxidase (DAO)
• Histamine N‑methyltransferase (HNMT)
• Monoamine oxidase B (MAO‑B)
• Catechol‑O‑methyltransferase (COMT)

Correct Answer: Diamine oxidase (DAO)

Q8. Which antihistamine is most likely to cause orthostatic hypotension due to alpha‑adrenergic blockade?

• Promethazine
• Fexofenadine
• Loratadine
• Famotidine

Correct Answer: Promethazine

Q9. Terfenadine was withdrawn from many markets because of what serious adverse effect when coadministered with CYP3A4 inhibitors?

• Torsades de pointes due to QT prolongation
• Severe hypoglycaemia
• Acute renal failure
• Excessive sedation

Correct Answer: Torsades de pointes due to QT prolongation

Q10. Which H1 antagonist is commonly used for its antiemetic and sedative properties in addition to antihistaminic action?

• Promethazine
• Ranitidine
• Fexofenadine
• Famotidine

Correct Answer: Promethazine

Q11. Blocking which receptor on gastric parietal cells reduces basal and stimulated acid secretion?

• H2 receptor
• H1 receptor
• H3 receptor
• H4 receptor

Correct Answer: H2 receptor

Q12. Which of the following is a second‑generation H1 antagonist with minimal sedation and low BBB penetration?

• Fexofenadine
• Chlorpheniramine
• Diphenhydramine
• Dimenhydrinate

Correct Answer: Fexofenadine

Q13. Which histamine receptor functions mainly as an autoreceptor in the CNS regulating histamine release?

• H3 receptor
• H1 receptor
• H2 receptor
• H4 receptor

Correct Answer: H3 receptor

Q14. Which histamine antagonist is clinically useful in Zollinger‑Ellison syndrome and severe peptic ulcer disease as an H2 blocker?

• Ranitidine
• Loratadine
• Diphenhydramine
• Terfenadine

Correct Answer: Ranitidine

Q15. A patient has acute anaphylaxis. Which statement is correct regarding antihistamines?

• Intramuscular epinephrine is first‑line; H1 antihistamines are adjunctive and not lifesaving
• Oral H1 antihistamines are sufficient as sole therapy
• H2 antagonists replace epinephrine in anaphylaxis management
• Prolonged H1 blockade prevents immediate airway compromise

Correct Answer: Intramuscular epinephrine is first‑line; H1 antihistamines are adjunctive and not lifesaving

Q16. Which H2 blocker has been associated historically with antiandrogenic effects such as gynecomastia?

• Cimetidine
• Famotidine
• Ranitidine
• Nizatidine

Correct Answer: Cimetidine

Q17. Histamine action on H1 receptors in blood vessels primarily causes which effect?

• Vasodilation and increased vascular permeability
• Vasoconstriction and decreased permeability
• Decreased heart rate via SA node inhibition
• Inhibition of gastric acid secretion

Correct Answer: Vasodilation and increased vascular permeability

Q18. Which property differentiates second‑generation H1 antihistamines from first‑generation agents?

• Less central sedation due to decreased lipid solubility and P‑glycoprotein efflux
• Greater antimuscarinic activity
• Stronger inhibition of gastric H2 receptors
• Higher propensity to cause orthostatic hypotension

Correct Answer: Less central sedation due to decreased lipid solubility and P‑glycoprotein efflux

Q19. Which enzyme methylates histamine in the central nervous system, aiding its inactivation?

• Histamine N‑methyltransferase (HNMT)
• Diamine oxidase (DAO)
• Monoamine oxidase A (MAO‑A)
• Glutathione S‑transferase

Correct Answer: Histamine N‑methyltransferase (HNMT)

Q20. Which H1 antagonist is an active metabolite of terfenadine with minimal cardiac risk and negligible CYP interaction?

• Fexofenadine
• Diphenhydramine
• Chlorpheniramine
• Promethazine

Correct Answer: Fexofenadine

Q21. Which clinical use is most appropriate for H2 antagonists?

• Peptic ulcer disease and GERD management
• Primary treatment of acute bronchospasm in asthma
• Topical treatment of contact dermatitis only
• First‑line therapy for anaphylactic shock

Correct Answer: Peptic ulcer disease and GERD management

Q22. Which antihistamine is likely to produce significant anticholinergic side effects like dry mouth and urinary retention?

• Diphenhydramine
• Fexofenadine
• Ranitidine
• Famotidine

Correct Answer: Diphenhydramine

Q23. Which H4 receptor function is being actively researched for therapeutic targeting?

• Modulation of immune cell chemotaxis and inflammation
• Control of gastric acid secretion in parietal cells
• Direct bronchial smooth muscle contraction
• Renal sodium reabsorption regulation

Correct Answer: Modulation of immune cell chemotaxis and inflammation

Q24. Which drug interaction risk is most important when prescribing cisapride historically with terfenadine?

• Both drugs metabolized by CYP3A4 can cause life‑threatening QT prolongation when combined
• They cause severe hypoglycaemia due to CYP induction
• Mutual antagonism at H1 receptors reduces efficacy
• They produce additive antimuscarinic effects causing constipation

Correct Answer: Both drugs metabolized by CYP3A4 can cause life‑threatening QT prolongation when combined

Q25. Which therapeutic effect is NOT typically produced by H1 antagonists?

• Reduction of immediate vasodilation and itching in urticaria
• Inhibition of gastric acid secretion comparable to H2 blockers
• Improvement of allergic rhinorrhoea and sneezing
• Adjunctive relief of pruritus in allergic dermatitis

Correct Answer: Inhibition of gastric acid secretion comparable to H2 blockers

Q26. Which pharmacokinetic property explains once‑daily dosing of some second‑generation antihistamines like cetirizine?

• Long half‑life permitting sustained receptor blockade
• Rapid renal clearance requiring multiple daily doses
• Extensive first‑pass metabolism to inactive compounds
• Requirement for frequent titration due to tolerance

Correct Answer: Long half‑life permitting sustained receptor blockade

Q27. Which statement correctly contrasts proton pump inhibitors (PPIs) with H2 blockers?

• PPIs irreversibly inhibit H+/K+ ATPase and provide more potent acid suppression than H2 blockers
• H2 blockers irreversibly inhibit proton pumps and are more potent than PPIs
• PPIs act on H2 receptors to reduce acid secretion
• H2 blockers block gastric proton pumps permanently

Correct Answer: PPIs irreversibly inhibit H+/K+ ATPase and provide more potent acid suppression than H2 blockers

Q28. Which adverse effect is classically associated with high doses of H2 blockers like cimetidine besides CYP inhibition?

• Gynecomastia and sexual dysfunction
• Severe bronchospasm
• Acute pancreatitis
• Myocardial infarction

Correct Answer: Gynecomastia and sexual dysfunction

Q29. Which laboratory enzyme measurement would be directly relevant when studying histamine catabolism in tissues?

• Diamine oxidase activity assay
• Alkaline phosphatase assay
• Creatine kinase assay
• Amylase assay

Correct Answer: Diamine oxidase activity assay

Q30. Which feature is important when choosing an antihistamine for a commercial driver who must avoid sedation?

• Select a non‑sedating second‑generation H1 antagonist such as loratadine or fexofenadine
• Choose a high‑potency first‑generation antihistamine like diphenhydramine
• Prefer promethazine for its strong sedative effect
• Combine H1 and H2 blockers to increase CNS depression

Correct Answer: Select a non‑sedating second‑generation H1 antagonist such as loratadine or fexofenadine

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.

Mail- Sachin@pharmacyfreak.com