Antitussives are drugs used to suppress coughing by modifying central or peripheral components of the cough reflex. This concise guide for B.Pharm students explains classification and detailed mechanisms of action, highlighting representative drugs such as codeine, dextromethorphan, benzonatate and levodropropizine. Key topics include central versus peripheral antitussives, opioid and non‑opioid mechanisms, CYP2D6 metabolism, pharmacokinetics, adverse effects, contraindications, drug interactions (for example dextromethorphan and serotonergic agents), pediatric warnings and abuse potential. Clinical dosing considerations and monitoring for safety are emphasized to support rational therapeutics and patient counselling. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which of the following best describes the primary mechanism of centrally acting antitussives?
- Suppressing the cough center in the medulla oblongata
- Breaking down mucus to facilitate expectoration
- Stimulating peripheral cough receptors in the airway
- Enhancing mucociliary clearance in bronchioles
Correct Answer: Suppressing the cough center in the medulla oblongata
Q2. Which drug is a classic opioid antitussive used historically for cough suppression?
- Benzonatate
- Codeine
- Guaifenesin
- Dextromethorphan
Correct Answer: Codeine
Q3. Dextromethorphan primarily exerts its antitussive activity via which mechanism?
- Local anesthesia of airway stretch receptors
- NMDA receptor antagonism and modulation of central cough pathways
- Inhibition of mucin secretion by airway glands
- Beta-2 adrenergic agonism causing bronchodilation
Correct Answer: NMDA receptor antagonism and modulation of central cough pathways
Q4. Benzonatate suppresses cough by which primary peripheral mechanism?
- Inhibition of hepatic metabolism of opioids
- Local anesthetic effect on pulmonary stretch receptors and vagal sensory endings
- Central mu‑opioid receptor activation
- Increasing bronchial secretions to dilute sputum
Correct Answer: Local anesthetic effect on pulmonary stretch receptors and vagal sensory endings
Q5. Which of the following is classified as a peripheral antitussive rather than a central antitussive?
- Codeine
- Dextromethorphan
- Benzonatate
- Hydrocodone
Correct Answer: Benzonatate
Q6. Which antitussive is also known for potential recreational abuse at high doses and dissociative effects?
- Guaifenesin
- Dextromethorphan
- Benzonatate
- Levodropropizine
Correct Answer: Dextromethorphan
Q7. Which enzyme is principally responsible for converting codeine into its active metabolite morphine?
- CYP3A4
- CYP2D6
- CYP1A2
Correct Answer: CYP2D6
Q8. Why are opioid antitussives like codeine contraindicated or used with caution in children?
- They cause bronchoconstriction in children exclusively
- Risk of respiratory depression, especially in CYP2D6 ultra‑rapid metabolizers
- They are ineffective against viral coughs in children
- They increase mucous production in pediatric airways
Correct Answer: Risk of respiratory depression, especially in CYP2D6 ultra‑rapid metabolizers
Q9. Which antitussive would be most inappropriate for a productive cough with thick purulent sputum?
- Expectorant such as guaifenesin
- Peripheral antitussive such as benzonatate
- Central opioid antitussive such as codeine
- Antibiotic therapy directed at infection
Correct Answer: Central opioid antitussive such as codeine
Q10. Levodropropizine is best described as which type of antitussive?
- Central opioid agonist acting on medullary cough center
- Peripheral antitussive that modulates sensory C‑fiber transmission
- Nucleoside analog that reduces viral cough sensitivity
- Expectorant that reduces mucus viscosity
Correct Answer: Peripheral antitussive that modulates sensory C‑fiber transmission
Q11. Which statement about guaifenesin is correct?
- It is a central antitussive that blocks NMDA receptors
- It is an expectorant that increases volume and decreases viscosity of respiratory secretions
- It is a local anesthetic used for airway desensitization
- It is a potent opioid analgesic with antitussive effects
Correct Answer: It is an expectorant that increases volume and decreases viscosity of respiratory secretions
Q12. Which drug interaction is of greatest concern when a patient takes dextromethorphan?
- Co-administration with beta‑blockers causing bronchospasm
- Combination with MAO inhibitors or SSRIs leading to serotonin syndrome
- Concurrent aspirin causing increased antitussive effect
- Combination with antacids reducing dextromethorphan absorption
Correct Answer: Combination with MAO inhibitors or SSRIs leading to serotonin syndrome
Q13. Which adverse effect is most characteristic of opioid antitussives?
- Excessive salivation and rhinorrhea
- Respiratory depression, sedation and constipation
- Bronchospasm and cough exacerbation
- Renal tubular necrosis
Correct Answer: Respiratory depression, sedation and constipation
Q14. What is the primary pharmacological distinction between antitussives and expectorants?
- Antitussives stimulate cough; expectorants suppress cough
- Antitussives suppress cough reflex; expectorants enhance clearance of secretions
- Both have identical mechanisms but different dosing
- Expectorants act in the brainstem while antitussives act peripherally
Correct Answer: Antitussives suppress cough reflex; expectorants enhance clearance of secretions
Q15. Which of the following is a non‑opioid, centrally acting antitussive available OTC in many countries?
- Codeine phosphate
- Dextromethorphan hydrobromide
- Benzonatate capsules
- Morphine sulfate
Correct Answer: Dextromethorphan hydrobromide
Q16. A patient chews benzonatate tablets and develops sudden numbness and choking sensation—this is most likely due to:
- Systemic opioid overdose
- Local anesthetic effect and possible topical anesthesia of the oropharynx causing aspiration risk
- Serotonin syndrome from interaction
- Allergic bronchospasm to benzonatate metabolites
Correct Answer: Local anesthetic effect and possible topical anesthesia of the oropharynx causing aspiration risk
Q17. Which antitussive’s action is reversed by naloxone in case of overdose?
- Levodropropizine
- Dextromethorphan
- Codeine
- Benzonatate
Correct Answer: Codeine
Q18. In patients with impaired CYP2D6 activity (poor metabolizers), what is the expected effect on codeine efficacy?
- Increased conversion to morphine and increased effect
- Reduced conversion to morphine and decreased antitussive effect
- No change in effect because codeine is active per se
- Immediate allergic reactions due to accumulation
Correct Answer: Reduced conversion to morphine and decreased antitussive effect
Q19. Which antitussive would you avoid prescribing to a patient on multiple serotonergic antidepressants?
- Benzonatate
- Guaifenesin
- Dextromethorphan
- Levodropropizine
Correct Answer: Dextromethorphan
Q20. For which clinical scenario are antitussives most appropriately used?
- Productive cough with purulent secretions due to bacterial pneumonia
- Nonproductive, distressing dry cough that disturbs sleep
- Acute asthma exacerbation with wheeze and thick sputum
- Pulmonary embolism causing hemoptysis
Correct Answer: Nonproductive, distressing dry cough that disturbs sleep
Q21. Which antitussive acts primarily by depressing the sensitivity of stretch receptors in the respiratory tract rather than central suppression?
- Dextromethorphan
- Codeine
- Benzonatate
- Hydrocodone
Correct Answer: Benzonatate
Q22. Which statement about dextromethorphan metabolism is correct?
- It is excreted unchanged in urine without hepatic metabolism
- It is metabolized in the liver to dextrorphan, which contributes to CNS effects
- It is converted to morphine by CYP2D6
- It is activated by esterases in the lung tissue
Correct Answer: It is metabolized in the liver to dextrorphan, which contributes to CNS effects
Q23. Which antitussive is most likely to cause constipation as a common adverse effect?
- Levodropropizine
- Dextromethorphan
- Codeine
- Benzonatate
Correct Answer: Codeine
Q24. What important counseling point should be given to patients taking antitussives for nonproductive cough?
- Antitussives improve mucus clearance and should be used with expectorants
- Avoid driving or operating machinery if sedated and follow dosing instructions to minimize CNS depression
- Always combine with antibiotics for best effect
- They are safe in all age groups including infants without dose adjustment
Correct Answer: Avoid driving or operating machinery if sedated and follow dosing instructions to minimize CNS depression
Q25. Which antitussive is contraindicated in children under 12 years old according to many regulatory authorities?
- Benzonatate
- Guaifenesin
- Codeine
- Dextromethorphan
Correct Answer: Codeine
Q26. Which of the following is NOT a recommended use for antitussives?
- Symptomatic relief of irritating dry cough
- Suppressing cough to improve sleep at night
- Routine suppression of productive cough with retained secretions
- Short‑term relief when cough causes pain after surgery
Correct Answer: Routine suppression of productive cough with retained secretions
Q27. Which antitussive has been associated with allergic reactions and should not be chewed or sucked?
- Dextromethorphan syrup
- Levodropropizine tablets
- Benzonatate capsules
- Guaifenesin tablets
Correct Answer: Benzonatate capsules
Q28. A patient presents with hallucinations and dissociation after overdosing on cough medicine containing dextromethorphan. This is due to excessive:
- Peripheral local anesthetic activity
- NMDA receptor antagonism and central dissociative effects of dextrorphan
- Anticholinergic blockade in peripheral tissues
- Beta‑adrenergic overstimulation
Correct Answer: NMDA receptor antagonism and central dissociative effects of dextrorphan
Q29. Which of the following antitussives is most appropriate for a patient with chronic liver failure requiring caution due to hepatic metabolism?
- Levodropropizine (minimal hepatic metabolism)
- Dextromethorphan (extensive hepatic metabolism)
- Benzonatate (exclusively renal excretion)
- Inhaled saline (systemic metabolism)
Correct Answer: Dextromethorphan (extensive hepatic metabolism)
Q30. When selecting an antitussive in clinical practice, which factors should a B.Pharm student consider?
- Mechanism of cough, drug mechanism, patient age, comorbidities, drug interactions and abuse potential
- Only the price and brand availability
- Prescription status only, regardless of cough type
- Using antitussives as first‑line for all coughs without evaluation
Correct Answer: Mechanism of cough, drug mechanism, patient age, comorbidities, drug interactions and abuse potential
