Introduction
Antihistamines are an important topic in pharmacology and are frequently studied by B.Pharm, D.Pharm, GPAT, and pharmacist recruitment exam candidates. These drugs are primarily used to manage allergic symptoms such as sneezing, itching, a runny nose, and urticaria.
Most antihistamines discussed in allergy treatment act on histamine H1 receptors. They are broadly classified into first-generation and second-generation antihistamines based on their pharmacological properties, including their ability to enter the central nervous system and cause sedation.
In this article, you will find 30 important antihistamines MCQs with answers and explanations covering drug classification, mechanism of action, therapeutic uses, adverse effects, and important pharmacological concepts.
These questions are useful for pharmacology revision, pharmacy examinations, and competitive pharmacist exams.
📝Antihistamines MCQs for Pharmacy Exams
1. Antihistamines primarily used to treat allergic conditions act on which receptor?
A. H1 receptor
B. H2 receptor
C. Dopamine receptor
D. Beta-adrenergic receptor
Correct Answer: A. H1 receptor
Explanation: H1 antihistamines reduce many symptoms of allergic reactions by acting as inverse agonists at histamine H1 receptors. They help relieve itching, sneezing, and other allergy symptoms.
2. Which of the following is a first-generation H1 antihistamine?
A. Fexofenadine
B. Loratadine
C. Diphenhydramine
D. Desloratadine
Correct Answer: C. Diphenhydramine
Explanation: Diphenhydramine is a first-generation antihistamine. It readily enters the central nervous system and may cause significant drowsiness.
3. Which of the following is a second-generation H1 antihistamine?
A. Promethazine
B. Chlorpheniramine
C. Diphenhydramine
D. Fexofenadine
Correct Answer: D. Fexofenadine
Explanation: Fexofenadine is a second-generation antihistamine with very low sedative potential compared with many first-generation agents.
4. Which adverse effect is commonly associated with first-generation antihistamines?
A. Sedation
B. Severe hypoglycaemia
C. Increased insulin secretion
D. Increased bone growth
Correct Answer: A. Sedation
Explanation: Many first-generation antihistamines cross the blood-brain barrier and block central H1 receptors, which can cause drowsiness and impaired alertness.
5. Which antihistamine is commonly associated with a lower risk of sedation?
A. Promethazine
B. Diphenhydramine
C. Fexofenadine
D. Hydroxyzine
Correct Answer: C. Fexofenadine
Explanation: Fexofenadine has very low penetration into the central nervous system and is generally less sedating than first-generation antihistamines. However, individual responses can vary.
6. Histamine is primarily stored in which cells involved in allergic reactions?
A. Mast cells
B. Red blood cells
C. Platelets only
D. Skeletal muscle cells
Correct Answer: A. Mast cells
Explanation: Mast cells store histamine in granules and release it during allergic and inflammatory responses. Basophils are another important source of histamine.
7. Which of the following is a common use of H1 antihistamines?
A. Treatment of bacterial infections
B. Relief of allergic rhinitis symptoms
C. Treatment of diabetes mellitus
D. Eradication of viral infections
Correct Answer: B. Relief of allergic rhinitis symptoms
Explanation: H1 antihistamines can relieve sneezing, itching, and a runny nose associated with allergic rhinitis. They do not treat the underlying cause of bacterial or viral infections.
8. Which first-generation antihistamine is commonly used to prevent motion sickness?
A. Fexofenadine
B. Loratadine
C. Dimenhydrinate
D. Desloratadine
Correct Answer: C. Dimenhydrinate
Explanation: Dimenhydrinate has antihistaminic and central nervous system effects that can help prevent motion sickness. It may cause drowsiness and other adverse effects.
9. Which of the following antihistamines is most likely to cause pronounced drowsiness?
A. Fexofenadine
B. Diphenhydramine
C. Loratadine
D. Desloratadine
Correct Answer: B. Diphenhydramine
Explanation: Diphenhydramine is a first-generation antihistamine that readily enters the brain. Its sedative effects can impair driving and other activities requiring alertness.
10. What is the primary pharmacological action of H1 antihistamines?
A. They stimulate histamine release.
B. They act as inverse agonists at H1 receptors.
C. They destroy histamine-producing cells.
D. They inhibit bacterial cell-wall synthesis.
Correct Answer: B. They act as inverse agonists at H1 receptors.
Explanation: H1 antihistamines stabilize the inactive state of H1 receptors, reducing histamine-mediated effects. They do not directly destroy histamine or histamine-producing cells.
11. Which of the following is a common symptom caused by histamine acting at H1 receptors?
A. Itching
B. Increased insulin production
C. Bone formation
D. Increased haemoglobin synthesis
Correct Answer: A. Itching
Explanation: Histamine acting at H1 receptors contributes to itching, vasodilation, increased vascular permeability, and other symptoms associated with allergic reactions.
12. Which group of antihistamines is more likely to cross the blood-brain barrier?
A. First-generation H1 antihistamines
B. All second-generation H1 antihistamines equally
C. Antibiotics
D. Antacids
Correct Answer: A. First-generation H1 antihistamines
Explanation: First-generation antihistamines generally enter the central nervous system more readily, increasing the risk of sedation and impaired alertness.
13. Which antihistamine is classified as a second-generation H1 blocker?
A. Chlorpheniramine
B. Promethazine
C. Loratadine
D. Diphenhydramine
Correct Answer: C. Loratadine
Explanation: Loratadine is a second-generation antihistamine used to relieve allergic rhinitis and urticaria symptoms. It generally causes less sedation than first-generation agents.
14. Which symptom can be relieved by an H1 antihistamine in a patient with an allergic reaction?
A. Itching
B. Bacterial resistance
C. Insulin deficiency
D. Bone fracture
Correct Answer: A. Itching
Explanation: H1 antihistamines help reduce histamine-mediated itching. They may also relieve sneezing and a runny nose, depending on the condition and the drug used.
15. Dry mouth caused by some first-generation antihistamines is mainly related to which action?
A. Anticholinergic action
B. Insulin stimulation
C. Increased thyroid hormone release
D. Beta-receptor stimulation
Correct Answer: A. Anticholinergic action
Explanation: Some first-generation antihistamines also block muscarinic acetylcholine receptors. This can cause dry mouth, blurred vision, constipation, and difficulty urinating.
16. Which drug is commonly used to relieve itching associated with urticaria?
A. Cetirizine
B. Metformin
C. Amoxicillin
D. Omeprazole
Correct Answer: A. Cetirizine
Explanation: Cetirizine is a second-generation H1 antihistamine used to relieve itching and wheals associated with urticaria. The appropriate treatment depends on the patient’s condition.
17. Promethazine belongs to which drug class?
A. Antihistamines
B. Penicillin antibiotics
C. Proton pump inhibitors
D. Oral antidiabetic drugs
Correct Answer: A. Antihistamines
Explanation: Promethazine is a first-generation H1 antihistamine with sedative and anticholinergic properties. It is also used for certain nausea and motion-sickness-related indications.
18. Which statement about second-generation antihistamines is generally correct?
A. They always cause severe sedation.
B. They generally cause less sedation than first-generation agents.
C. They are all antibiotics.
D. They work by destroying histamine-producing cells.
Correct Answer: B. They generally cause less sedation than first-generation agents.
Explanation: Second-generation antihistamines generally have less central nervous system penetration. Some, such as cetirizine, can still cause drowsiness in certain individuals.
19. Which of the following is a common adverse effect of some first-generation antihistamines?
A. Dry mouth
B. Increased insulin secretion
C. Permanent hair growth
D. Increased bone length
Correct Answer: A. Dry mouth
Explanation: Anticholinergic effects can cause dry mouth and other symptoms, including constipation and blurred vision. The likelihood and severity depend on the specific drug and patient.
20. Which patients require particular caution when using antihistamines with strong anticholinergic effects?
A. Patients with narrow-angle glaucoma
B. Patients with uncomplicated seasonal allergies only
C. All healthy adults equally
D. Patients with normal vision only
Correct Answer: A. Patients with narrow-angle glaucoma
Explanation: Anticholinergic medicines can increase intraocular pressure in susceptible patients with narrow-angle glaucoma. Drug selection should take account of the patient’s medical history and the specific antihistamine.
21. Do antihistamines cure the common cold?
A. Yes, all antihistamines eliminate the virus.
B. Yes, they replace antiviral treatment in every case.
C. No, some may relieve selected symptoms but do not cure the infection.
D. Yes, they destroy bacteria and viruses directly.
Correct Answer: C. No, some may relieve selected symptoms but do not cure the infection.
Explanation: Some first-generation antihistamines may provide limited relief of a runny nose and sneezing associated with the common cold. They do not eliminate the virus responsible for the infection.
22. The term antipruritic refers to a drug that helps relieve:
A. Itching
B. Fever
C. High blood glucose
D. Bacterial infection
Correct Answer: A. Itching
Explanation: Antipruritic medicines reduce itching. H1 antihistamines can be useful when itching is related to histamine-mediated conditions such as urticaria.
23. Which histamine receptor is most closely associated with gastric acid secretion?
A. H1
B. H2
C. H3
D. H4
Correct Answer: B. H2
Explanation: H2 receptors in gastric parietal cells mediate histamine-stimulated acid secretion. H2 blockers, such as famotidine, are used to reduce gastric acid production.
24. Which of the following is a second-generation antihistamine with very low sedative potential?
A. Promethazine
B. Diphenhydramine
C. Fexofenadine
D. Hydroxyzine
Correct Answer: C. Fexofenadine
Explanation: Fexofenadine generally has minimal sedative effects compared with first-generation antihistamines. Nevertheless, patients should assess their individual response when taking any medicine.
25. Why should first-generation antihistamines be used cautiously in older adults?
A. They always cause severe hypertension.
B. Their sedative and anticholinergic effects can increase the risk of confusion and falls.
C. They always cause kidney failure.
D. They increase insulin secretion in every patient.
Correct Answer: B. Their sedative and anticholinergic effects can increase the risk of confusion and falls.
Explanation: Older adults can be particularly sensitive to sedation, confusion, constipation, urinary retention, and other anticholinergic effects. The suitability of a drug should be assessed individually.
26. Which antihistamine is a first-generation drug?
A. Desloratadine
B. Fexofenadine
C. Chlorpheniramine
D. Loratadine
Correct Answer: C. Chlorpheniramine
Explanation: Chlorpheniramine is a first-generation H1 antihistamine used for certain allergic symptoms. It can cause drowsiness and anticholinergic adverse effects.
27. Which of the following is a potential consequence of sedation caused by first-generation antihistamines?
A. Improved reaction time in every patient
B. Impaired driving ability
C. Complete prevention of allergies
D. Increased resistance to infections
Correct Answer: B. Impaired driving ability
Explanation: Sedating antihistamines can impair alertness, coordination, and reaction time. Patients should avoid driving or operating machinery if affected.
28. Which of the following is the active metabolite of loratadine?
A. Desloratadine
B. Fexofenadine
C. Diphenhydramine
D. Promethazine
Correct Answer: A. Desloratadine
Explanation: Loratadine is metabolized to desloratadine, which is itself an active antihistamine. Both drugs are classified as second-generation H1 antihistamines.
29. Which drug class reduces histamine-stimulated gastric acid secretion by blocking H2 receptors?
A. H1 antihistamines
B. H2 receptor antagonists
C. Beta-adrenergic agonists
D. Antimuscarinic antibiotics
Correct Answer: B. H2 receptor antagonists
Explanation: H2 receptor antagonists, such as famotidine, block histamine H2 receptors in gastric parietal cells and reduce acid secretion. They differ from H1 antihistamines used for allergic symptoms.
30. Which statement best describes the principal use of H1 antihistamines?
A. They cure all allergic diseases permanently.
B. They help relieve symptoms of certain histamine-mediated conditions.
C. They eliminate all viruses.
D. They replace emergency treatment for every severe allergic reaction.
Correct Answer: B. They help relieve symptoms of certain histamine-mediated conditions.
Explanation: H1 antihistamines are used to relieve symptoms associated with conditions such as allergic rhinitis and urticaria. They do not cure every allergic disease, and they must not replace intramuscular adrenaline (epinephrine) as the first-line treatment for anaphylaxis.
📑Important Points to Remember
- First-generation antihistamines: Diphenhydramine, promethazine, chlorpheniramine, and dimenhydrinate.
- Second-generation antihistamines: Cetirizine, loratadine, desloratadine, and fexofenadine.
- Mechanism: H1 antihistamines act as inverse agonists at H1 receptors.
- Common adverse effects: Sedation and anticholinergic effects are particularly important with many first-generation drugs.
- Allergic rhinitis: H1 antihistamines can relieve sneezing, itching, and a runny nose.
- Urticaria: Second-generation H1 antihistamines are commonly used to relieve itching and wheals.
- Motion sickness: Certain first-generation antihistamines, including dimenhydrinate, can help prevent symptoms.
- H2 receptors: These receptors are associated with gastric acid secretion and are targeted by drugs such as famotidine.
🎯 Conclusion
Antihistamines are important drugs in pharmacology because of their role in managing allergic symptoms and selected other conditions. For examinations, focus on their classification, mechanism of action, therapeutic uses, and adverse effects.
Explore more pharmacology MCQs and pharmacy notes on PharmaLearn Hub to continue your exam preparation.
Educational disclaimer: This article is intended for educational and examination-preparation purposes. It does not replace professional medical advice or individualized treatment.
1 thought on “Top 30 MCQs on Antihistamines with Answers & Explanation”