Clemastine fumarate is a first‑generation H1 receptor antagonist widely studied in pharmacology and therapeutics. This antihistamine exhibits potent blockade of histamine‑mediated effects, with notable central nervous system penetration that causes sedation and anticholinergic adverse effects. B. Pharm students should focus on clemastine’s mechanism of action, clinical indications (allergic rhinitis, urticaria, pruritus), pharmacokinetics (hepatic metabolism, renal excretion), drug interactions (CNS depressants, anticholinergic agents), contraindications, and toxicity management. Understanding formulation, dosing principles, and patient counseling (sedation, alcohol avoidance) is essential for safe use. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary mechanism of action of clemastine fumarate?
- Beta‑2 adrenergic agonism
- H1 receptor antagonist (inverse agonist)
- Leukotriene receptor antagonism
- Cyclooxygenase inhibition
Correct Answer: H1 receptor antagonist (inverse agonist)
Q2. Clemastine fumarate belongs to which class of antihistamines?
- Second‑generation H1 antagonists
- H2 receptor antagonists
- First‑generation H1 antagonists
- Corticosteroids
Correct Answer: First‑generation H1 antagonists
Q3. Which clinical condition is a primary indication for clemastine?
- Type 1 diabetes
- Allergic rhinitis and urticaria
- Bacterial sinusitis
- Chronic kidney disease
Correct Answer: Allergic rhinitis and urticaria
Q4. A prominent central adverse effect of clemastine is:
- Hyperactivity
- Sedation and drowsiness
- Increased appetite
- Insomnia
Correct Answer: Sedation and drowsiness
Q5. Which anticholinergic side effect is commonly associated with clemastine?
- Diarrhea
- Excessive lacrimation
- Dry mouth
- Bradykinesia
Correct Answer: Dry mouth
Q6. Co‑administration of clemastine with which substance increases risk of sedation?
- Vitamin C
- Alcohol
- Ibuprofen
- Famotidine
Correct Answer: Alcohol
Q7. Common pharmaceutical formulations of clemastine include:
- Intravenous infusion only
- Topical gel only
- Oral tablets and syrup
- Inhaler
Correct Answer: Oral tablets and syrup
Q8. Clemastine is generally contraindicated in which patient group?
- Healthy adults aged 25–40
- Newborns and premature infants
- Patients with seasonal allergies
- Patients with controlled hypertension
Correct Answer: Newborns and premature infants
Q9. Overdose of clemastine most likely produces which toxidrome?
- Cholinergic toxidrome
- Opioid toxidrome
- Anticholinergic toxidrome (hyperthermia, dry skin, delirium)
- Benzodiazepine toxidrome
Correct Answer: Anticholinergic toxidrome (hyperthermia, dry skin, delirium)
Q10. The onset of therapeutic action after oral dosing of clemastine is typically:
- Within minutes
- Approximately 1 hour
- After 48 hours
- After one week
Correct Answer: Approximately 1 hour
Q11. Clemastine’s duration of action is best described as:
- Ultra‑short (less than 2 hours)
- Short (2–4 hours)
- Intermediate to long (around 12 hours or more)
- Permanent
Correct Answer: Intermediate to long (around 12 hours or more)
Q12. The primary organ system responsible for clemastine metabolism is the:
- Renal glomerulus
- Hepatic microsomal system
- Pulmonary epithelium
- Gastrointestinal flora
Correct Answer: Hepatic microsomal system
Q13. Major route of elimination for clemastine and its metabolites is:
- Fecal elimination only
- Urinary excretion
- Exhalation via lungs
- Secretion in sweat
Correct Answer: Urinary excretion
Q14. Clemastine’s ability to cause sedation is largely due to its:
- High renal clearance
- Poor oral absorption
- Penetration across the blood–brain barrier
- Activation of H2 receptors
Correct Answer: Penetration across the blood–brain barrier
Q15. In patients with narrow‑angle glaucoma, clemastine should be:
- Used at high doses for symptom relief
- Used with caution or avoided due to anticholinergic effects
- Only administered intravenously
- Combined with antimuscarinic drugs
Correct Answer: Used with caution or avoided due to anticholinergic effects
Q16. The term “fumarate” in clemastine fumarate refers to:
- A prodrug activation step in vivo
- The fumaric acid salt form used for stability and formulation
- A method of topical delivery
- An inactive impurity
Correct Answer: The fumaric acid salt form used for stability and formulation
Q17. Clemastine is NOT recommended as primary therapy for which condition?
- Allergic rhinitis
- Acute anaphylactic shock (without epinephrine)
- Chronic urticaria (adjunctive use)
- Pruritus of allergic origin
Correct Answer: Acute anaphylactic shock (without epinephrine)
Q18. The antihistamine effect of clemastine reduces allergy symptoms primarily by:
- Stimulating histamine release from mast cells
- Blocking histamine‑induced vasodilation and increased vascular permeability
- Increasing leukotriene synthesis
- Inhibiting IgG production
Correct Answer: Blocking histamine‑induced vasodilation and increased vascular permeability
Q19. Which cardiovascular effect can occur with clemastine due to its anticholinergic action?
- Bradycardia with heart block
- Tachycardia
- Profound hypotension only
- Cardiac glycoside potentiation exclusively
Correct Answer: Tachycardia
Q20. Which drug class can potentiate anticholinergic and sedative effects when combined with clemastine?
- Selective serotonin reuptake inhibitors (SSRIs)
- Tricyclic antidepressants (TCAs)
- Thyroid hormones
- Oral contraceptives
Correct Answer: Tricyclic antidepressants (TCAs)
Q21. Besides H1 receptors, clemastine exhibits clinically relevant blockade of which receptor type?
- Beta‑1 adrenergic receptors
- Muscarinic acetylcholine receptors
- Insulin receptors
- Dopamine D2 receptors
Correct Answer: Muscarinic acetylcholine receptors
Q22. Key patient counseling point for clemastine therapy is:
- It enhances alertness and is safe for driving
- Avoid alcohol and activities requiring mental alertness due to sedation
- It cures the underlying allergic sensitization permanently
- No interactions with other CNS depressants
Correct Answer: Avoid alcohol and activities requiring mental alertness due to sedation
Q23. Pediatric use of clemastine requires special caution because:
- Children always metabolize it faster so doses should be increased
- Young children are more sensitive to paradoxical CNS and anticholinergic effects
- It is an effective stimulant in children
- It is recommended as first‑line for febrile seizures
Correct Answer: Young children are more sensitive to paradoxical CNS and anticholinergic effects
Q24. Blurred vision associated with clemastine is primarily due to:
- Retinal detachment
- Mydriasis and impaired accommodation from anticholinergic action
- Increased lacrimation
- Narrow‑angle miosis
Correct Answer: Mydriasis and impaired accommodation from anticholinergic action
Q25. Which urinary symptom may be precipitated by clemastine in susceptible patients?
- Polyuria
- Urinary retention
- Nephrotic syndrome
- Glucosuria
Correct Answer: Urinary retention
Q26. The primary therapeutic target receptor for alleviating histamine‑mediated allergic symptoms is:
- H3 receptor
- H1 receptor
- H4 receptor
- H2 receptor
Correct Answer: H1 receptor
Q27. A patient with benign prostatic hyperplasia (BPH) should use clemastine:
- With caution because of risk of worsening urinary retention
- Without concern; antihistamines do not affect urinary function
- Only at double the usual dose
- As an injectable in preference to oral therapy
Correct Answer: With caution because of risk of worsening urinary retention
Q28. In case of severe agitation or seizures from clemastine overdose, the first‑line management for seizures is typically:
- Activated charcoal only
- Benzodiazepines for seizure control
- Beta‑blockers to slow heart rate
- Immediate oral antidote administration
Correct Answer: Benzodiazepines for seizure control
Q29. With repeated short‑term use, which clinical effect of clemastine is most likely to show tolerance?
- Anticholinergic dry mouth
- Sedative effect
- Permanent increase in histamine production
- Immediate hypersensitivity to drug excipients
Correct Answer: Sedative effect
Q30. Which statement best describes clemastine fumarate’s dosing frequency in typical clinical use?
- Given as a continuous intravenous infusion
- Usually administered twice daily due to intermediate‑long duration
- Taken once every 7 days
- Used only as needed during anaphylactic shock
Correct Answer: Usually administered twice daily due to intermediate‑long duration
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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