Pharmacology Quiz: Autacoids & Antihistamines (MCQs with Answers & Explanations)

If you're preparing for medical, pharmacist, or pharmacology exams, this quiz will test your knowledge on autacoids, histamine, and antihistamines. Below are 30 multiple-choice questions (MCQs) with detailed explanations to help you understand key concepts.

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Quiz Questions & Answers

1. Autacoids differ from hormones in that:

Options:
A) Autacoids are involved only in the causation of pathological states
B) Autacoids do not have a specific cell/tissue of origin
C) Autacoids generally act locally at the site of generation and release
D) Both 'B' and 'C' are correct

✅ Correct Answer: D (Both 'B' and 'C' are correct)
📝 Explanation: Autacoids are local hormones that act near their site of synthesis and generally do not enter systemic circulation like endocrine hormones. They are not limited to pathological conditions and do not have a well-defined site of origin.

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2. Which of the following is a selective H2 receptor agonist?

Options:
A) 4-methyl histamine
B) Impromidine
C) 2-Thiazolylethylamine
D) Chlorpheniramine

✅ Correct Answer: B (Impromidine)
📝 Explanation: Impromidine is a potent and selective H2 receptor agonist used primarily in research to study histamine's action on the gastric mucosa. It helps stimulate gastric acid secretion and is much more specific than other histamine analogs.

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3. The action of histamine that is not mediated through H1 receptors is:

Options:
A) Release of EDRF from vascular endothelium resulting in vasodilatation
B) Direct action on vascular smooth muscle causing vasodilatation
C) Bronchoconstriction
D) Release of catecholamines from adrenal medulla

✅ Correct Answer: D (Release of catecholamines from adrenal medulla)
📝 Explanation: While most histamine actions such as bronchoconstriction and vasodilation are mediated by H1 receptors, the release of catecholamines from the adrenal medulla occurs via H2 receptors.

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4. Histamine exerts the following actions except:

Options:
A) Dilatation of large blood vessels
B) Dilatation of small blood vessels
C) Stimulation of isolated guinea pig heart
D) Itching

✅ Correct Answer: A (Dilatation of large blood vessels)
📝 Explanation: Histamine primarily causes vasodilation in small vessels like capillaries and arterioles, not large blood vessels. Itching is mediated through sensory nerve endings, and it can stimulate isolated heart tissues in lab studies.

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5. Fall in blood pressure caused by larger doses of histamine is blocked by:

Options:
A) H1 antihistamines alone
B) H2 antagonists alone
C) Combination of H1 and H2 antagonists
D) None of the above

✅ Correct Answer: C (Combination of H1 and H2 antagonists)
📝 Explanation: Large doses of histamine can lead to hypotension through both H1 and H2 receptor activation—H1 causing vasodilation and increased permeability, and H2 contributing to vasodilation. Blocking both receptors is necessary to effectively counter the drop in blood pressure.

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6. Which of the following antihistamines has prominent anti-serotonin activity?

Options:
A) Diphenhydramine
B) Mepyramine
C) Cyproheptadine
D) Promethazine

✅ Correct Answer: C (Cyproheptadine)
📝 Explanation: Cyproheptadine is a first-generation antihistamine that not only blocks H1 receptors but also has significant anti-serotonergic properties. It is used in conditions like serotonin syndrome and can stimulate appetite due to serotonin blockade in the hypothalamus.

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7. All of the following statements about H1 antihistamines are correct, except:

Options:
A) They do not inhibit release of histamine
B) They are more effective in preventing symptoms
C) They are ineffective in asthma
D) They are useful in motion sickness only when administered orally

✅ Correct Answer: D (They are useful in motion sickness only when administered orally)
📝 Explanation: H1 antihistamines like promethazine are effective in treating motion sickness, but their route of administration isn't limited to oral use. They can also be given via other routes like IM or IV in certain situations.

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8. The most prominent action of H1 antihistamines is:

Options:
A) Bronchodilation
B) Antipruritic and anti-inflammatory effect
C) Reduction of gastric acid secretion
D) Prevention of delayed hypersensitivity reactions

✅ Correct Answer: B (Antipruritic and anti-inflammatory effect)
📝 Explanation: H1 antihistamines are primarily used for their antipruritic and anti-inflammatory effects in allergic conditions like urticaria and hay fever. They block histamine's action at H1 receptors, reducing itching, swelling, and redness.

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9. Which of the following second-generation H1 antihistamines is most sedating?

Options:
A) Fexofenadine
B) Loratadine
C) Cetirizine
D) Levocetirizine

✅ Correct Answer: C (Cetirizine)
📝 Explanation: Cetirizine, although classified as a second-generation antihistamine, can still cause sedation in some individuals. It is less sedating than first-generation drugs but more than other second-gen agents like fexofenadine or loratadine.

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10. A prominent use of promethazine is:

Options:
A) As a sedative in children
B) For treating peptic ulcer
C) As an anti-inflammatory agent
D) To stimulate appetite

✅ Correct Answer: A (As a sedative in children)
📝 Explanation: Promethazine is a first-generation H1 blocker with strong sedative effects and is often used to treat nausea, vomiting, and motion sickness. In pediatric practice, it is used cautiously as a sedative due to its pronounced CNS depressant activity.

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11. Terfenadine does not cause sedation because:

Options:
A) It does not cross the blood-brain barrier
B) It is a weak H1 receptor antagonist
C) It has no action on CNS histamine receptors
D) It is quickly eliminated from the body

✅ Correct Answer: A (It does not cross the blood-brain barrier)
📝 Explanation: Terfenadine is a second-generation antihistamine that doesn't cross the blood-brain barrier, preventing it from acting on central H1 receptors. This property reduces sedative effects compared to first-generation antihistamines.

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12. Antihistamines acting at H2 receptors are used in:

Options:
A) Bronchial asthma
B) Anaphylactic shock
C) Peptic ulcer
D) Urticaria

✅ Correct Answer: C (Peptic ulcer)
📝 Explanation: H2 receptor antagonists like ranitidine reduce gastric acid secretion and are primarily used for peptic ulcers and GERD by blocking histamine-mediated acid release from gastric parietal cells.

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13. Which drug can be safely used for allergic rhinitis in hypertensive patients?

Options:
A) Chlorpheniramine
B) Phenylephrine
C) Cetirizine
D) Pseudoephedrine

✅ Correct Answer: C (Cetirizine)
📝 Explanation: Cetirizine is safe for hypertension patients as it lacks the cardiovascular effects of sympathomimetics like pseudoephedrine which can raise blood pressure.

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14. Side effect of first-generation antihistamines includes:

Options:
A) Diarrhea
B) Salivation
C) Dry mouth
D) Increased urination

✅ Correct Answer: C (Dry mouth)
📝 Explanation: Their anticholinergic properties cause dry mouth, constipation, urinary retention, and blurred vision via muscarinic receptor blockade.

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15. Which antihistamine has marked antiemetic property?

Options:
A) Hydroxyzine
B) Diphenhydramine
C) Chlorpheniramine
D) Fexofenadine

✅ Correct Answer: B (Diphenhydramine)
📝 Explanation: Its ability to block histamine and muscarinic receptors in the brain's vomiting center makes it effective against nausea and motion sickness.

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16. Most common side effect of H1 antihistamines is:

Options:
A) Diarrhea
B) Sedation
C) Hypertension
D) Tachycardia

✅ Correct Answer: B (Sedation)
📝 Explanation: First-generation drugs readily cross the blood-brain barrier, blocking central histamine receptors involved in wakefulness.

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17. Which antihistamine prolongs QT interval and may cause arrhythmias?

Options:
A) Loratadine
B) Fexofenadine
C) Terfenadine
D) Cetirizine

✅ Correct Answer: C (Terfenadine)
📝 Explanation: Its cardiotoxic effects led to withdrawal in many countries, with fexofenadine being its safer metabolite.

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18. H1 receptor antagonists are NOT useful in:

Options:
A) Motion sickness
B) Anaphylaxis
C) Allergic rhinitis
D) Peptic ulcer

✅ Correct Answer: D (Peptic ulcer)
📝 Explanation: Peptic ulcers are mediated by H2 receptors, making H1 blockers ineffective for this condition.

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19. Characteristic of second-generation antihistamines:

Options:
A) High sedative effect
B) Lipophilic and cross BBB
C) Short duration of action
D) Minimal CNS side effects

✅ Correct Answer: D (Minimal CNS side effects)
📝 Explanation: Their peripheral selectivity and poor BBB penetration reduce sedation risk.

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20. Which is NOT an H1-antihistamine?

Options:
A) Hydroxyzine
B) Cimetidine
C) Diphenhydramine
D) Loratadine

✅ Correct Answer: B (Cimetidine)
📝 Explanation: Cimetidine is an H2 blocker used for gastric acid reduction, not allergies.

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21. Which is a mast cell stabilizer?

Options:
A) Chlorpheniramine
B) Loratadine
C) Sodium cromoglycate
D) Hydroxyzine

✅ Correct Answer: C (Sodium cromoglycate)
📝 Explanation: It prevents mast cell degranulation, useful in asthma and allergic conjunctivitis prophylaxis.

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22. Drug used in anaphylactic shock:

Options:
A) Loratadine
B) Hydroxyzine
C) Adrenaline
D) Diphenhydramine

✅ Correct Answer: C (Adrenaline)
📝 Explanation: First-line treatment for anaphylaxis due to its α/β adrenergic effects that counteract shock.

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23. Diphenhydramine can be used in:

Options:
A) Motion sickness
B) Parkinsonism
C) Allergic rhinitis
D) All of the above

✅ Correct Answer: D (All of the above)
📝 Explanation: Its anticholinergic effects make it versatile for these indications.

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24. First-generation H1 blocker:

Options:
A) Fexofenadine
B) Loratadine
C) Cetirizine
D) Hydroxyzine

✅ Correct Answer: D (Hydroxyzine)
📝 Explanation: It crosses the BBB readily, causing significant sedation.

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25. Least sedative antihistamine:

Options:
A) Diphenhydramine
B) Hydroxyzine
C) Cetirizine
D) Chlorpheniramine

✅ Correct Answer: C (Cetirizine)
📝 Explanation: Among these, cetirizine has the lowest CNS penetration.

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26. H1 blockers are used in:

Options:
A) Anaphylaxis
B) Peptic ulcer
C) Motion sickness
D) Both a and c

✅ Correct Answer: D (Both a and c)
📝 Explanation: They're adjuncts in anaphylaxis and primary treatment for motion sickness.

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27. Antihistamine with antiemetic action:

Options:
A) Diphenhydramine
B) Chlorpheniramine
C) Loratadine
D) Cetirizine

✅ Correct Answer: A (Diphenhydramine)
📝 Explanation: Its anticholinergic action on the vomiting center provides antiemetic effects.

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28. Selective H2 blocker:

Options:
A) Ranitidine
B) Chlorpheniramine
C) Diphenhydramine
D) Loratadine

✅ Correct Answer: A (Ranitidine)
📝 Explanation: Reduces gastric acid secretion via H2 receptor blockade.

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29. Ranitidine is used for:

Options:
A) Peptic ulcer
B) Anaphylaxis
C) Asthma
D) Nasal congestion

✅ Correct Answer: A (Peptic ulcer)
📝 Explanation: Its H2 antagonism makes it effective for acid-related disorders.

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30. Cimetidine is a:

Options:
A) H1 blocker
B) H2 blocker
C) Cholinergic blocker
D) None of the above

✅ Correct Answer: B (H2 blocker)
📝 Explanation: The prototype H2 antagonist that revolutionized ulcer treatment.

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