Macrolide antibiotics — erythromycin, clarithromycin and azithromycin — are essential for B.Pharm students to master due to their widespread use in respiratory, soft tissue and atypical infections. This concise, keyword-rich introduction covers mechanism of action (50S ribosomal inhibition), pharmacokinetics (absorption, distribution, long tissue half-life of azithromycin), clinical spectrum, resistance mechanisms (erm methylation, mef efflux), adverse effects (GI upset, hepatotoxicity, QT prolongation), and major drug interactions (CYP3A4 inhibition). Emphasis is placed on comparative features, formulations and therapeutic uses to support exam preparation and rational dispensing. Questions include detailed pharmacology, therapeutic uses, adverse reactions and exam-style recall to boost mastery. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which is the primary mechanism of action of macrolide antibiotics?
- Inhibition of cell wall peptidoglycan synthesis
- Inhibition of DNA gyrase
- Inhibition of 50S ribosomal translocation
- Disruption of bacterial cell membrane
Correct Answer: Inhibition of 50S ribosomal translocation
Q2. Macrolides bind primarily to which component of the bacterial ribosome?
- 16S rRNA of 30S subunit
- 23S rRNA of 50S subunit
- 5S rRNA of 50S subunit
- L9 ribosomal protein
Correct Answer: 23S rRNA of 50S subunit
Q3. Macrolides are particularly effective against which group of pathogens?
- Enterobacteriaceae (e.g., E. coli)
- Anaerobes exclusively
- Atypical pathogens such as Mycoplasma, Chlamydia and Legionella
- Pseudomonas aeruginosa
Correct Answer: Atypical pathogens such as Mycoplasma, Chlamydia and Legionella
Q4. Which macrolide formulation is most acid-labile and therefore degraded in the stomach?
- Erythromycin base
- Azithromycin
- Clarithromycin
- Erythromycin ethylsuccinate
Correct Answer: Erythromycin base
Q5. Which macrolide has the longest tissue half-life allowing once-daily or short-course regimens?
- Erythromycin
- Clarithromycin
- Azithromycin
- Roxithromycin
Correct Answer: Azithromycin
Q6. Which macrolide is commonly associated with prokinetic activity via motilin receptor agonism?
- Azithromycin
- Clarithromycin
- Erythromycin
- Telithromycin
Correct Answer: Erythromycin
Q7. Which macrolide has the least effect on CYP3A4-mediated drug interactions?
- Erythromycin
- Clarithromycin
- Azithromycin
- Dirithromycin
Correct Answer: Azithromycin
Q8. A major cardiac safety concern shared by many macrolides is:
- Severe hypertension
- QT interval prolongation and risk of torsades de pointes
- Bradycardia due to beta-blocking effects
- Acute myocardial infarction
Correct Answer: QT interval prolongation and risk of torsades de pointes
Q9. The erm gene confers macrolide resistance by which mechanism?
- Production of beta-lactamase enzyme
- Efflux pump removing the drug from the cell
- Methylation of 23S rRNA leading to target modification
- Enzymatic hydrolysis of the macrolide lactone ring
Correct Answer: Methylation of 23S rRNA leading to target modification
Q10. Which macrolide is commonly used as part of empirical triple therapy for Helicobacter pylori eradication?
- Erythromycin
- Clarithromycin
- Azithromycin
- Linezolid
Correct Answer: Clarithromycin
Q11. Use of which macrolide in neonates has been associated with increased risk of infantile hypertrophic pyloric stenosis?
- Azithromycin
- Clarithromycin
- Erythromycin
- Roxithromycin
Correct Answer: Erythromycin
Q12. Which macrolide is generally considered safest in pregnancy (category B in many sources)?
- Erythromycin estolate
- Clarithromycin
- Azithromycin
- Telithromycin
Correct Answer: Azithromycin
Q13. Which macrolide is commonly used for prophylaxis or treatment of Mycobacterium avium complex (MAC) in HIV patients?
- Erythromycin
- Clarithromycin
- Azithromycin
- Fidaxomicin
Correct Answer: Azithromycin
Q14. Co-administration of clarithromycin with warfarin is most likely to cause which effect?
- Decreased INR and reduced anticoagulant effect
- Increased INR and enhanced anticoagulant effect
- No interaction
- Immediate bleeding unrelated to INR
Correct Answer: Increased INR and enhanced anticoagulant effect
Q15. Which property explains azithromycin’s high tissue concentrations and prolonged post-antibiotic effect?
- High renal excretion unchanged
- Extensive intracellular accumulation in phagocytes and fibroblasts
- Strong plasma protein binding preventing tissue uptake
- Rapid hepatic metabolism to inactive metabolites
Correct Answer: Extensive intracellular accumulation in phagocytes and fibroblasts
Q16. Which erythromycin formulation has been associated with cholestatic hepatitis and is therefore used cautiously?
- Erythromycin ethylsuccinate
- Erythromycin estolate
- Erythromycin stearate
- Erythromycin base
Correct Answer: Erythromycin estolate
Q17. Macrolides are classified pharmacodynamically as primarily:
- Bactericidal agents against all organisms
- Bacteriostatic agents, although concentration-dependent killing can occur
- Fungicidal agents
- Virucidal agents
Correct Answer: Bacteriostatic agents, although concentration-dependent killing can occur
Q18. The current preferred macrolide for treatment of pertussis in most age groups is:
- Erythromycin
- Clarithromycin
- Azithromycin
- Doxycycline
Correct Answer: Azithromycin
Q19. Which macrolide acts as an agonist at motilin receptors and can accelerate gastric emptying?
- Clarithromycin
- Azithromycin
- Erythromycin
- Troleandomycin
Correct Answer: Erythromycin
Q20. Which dosing feature is characteristic of azithromycin compared to erythromycin and clarithromycin?
- Requires multiple daily dosing due to short half-life
- Once-daily dosing and shorter courses due to long tissue half-life
- Administered only intravenously
- Requires co-administration with proton pump inhibitors
Correct Answer: Once-daily dosing and shorter courses due to long tissue half-life
Q21. Co-administration of which statin with clarithromycin poses a higher risk of myopathy due to CYP3A4 inhibition?
- Pravastatin
- Rosuvastatin
- Atorvastatin
- Fluvastatin
Correct Answer: Atorvastatin
Q22. Structurally, azithromycin differs from erythromycin by:
- Being a lincosamide rather than a macrolide
- Having a 15-membered azalide ring instead of a 14-membered macrolide ring
- Lack of a lactone ring entirely
- Possessing a thiazole ring substitution
Correct Answer: Having a 15-membered azalide ring instead of a 14-membered macrolide ring
Q23. Which macrolide demonstrates enhanced activity against many respiratory Gram-negative pathogens compared to erythromycin?
- Erythromycin
- Azithromycin
- Vancomycin
- Trimethoprim
Correct Answer: Azithromycin
Q24. Co-administration of erythromycin with cisapride (a prokinetic) historically caused a dangerous interaction characterized by:
- Severe hypoglycemia
- Life-threatening QT prolongation and torsades de pointes
- Acute renal failure due to crystal formation
- Marked hypertension and stroke
Correct Answer: Life-threatening QT prolongation and torsades de pointes
Q25. Which macrolide is most commonly selected for community-acquired pneumonia due to atypical pathogens and used empirically in outpatient settings?
- Vancomycin
- Clarithromycin
- Amoxicillin
- Metronidazole
Correct Answer: Clarithromycin
Q26. Absorption of erythromycin base is most affected by which factor?
- Food decreases absorption of erythromycin base
- Food increases absorption markedly
- Antacids enhance absorption
- Administration with dairy products prevents absorption
Correct Answer: Food decreases absorption of erythromycin base
Q27. Clarithromycin is primarily metabolized by which hepatic enzyme system?
- CYP2D6
- CYP3A4
- Monoamine oxidase (MAO)
- Glutathione S-transferase (GST)
Correct Answer: CYP3A4
Q28. For patients with a severe penicillin allergy requiring treatment of streptococcal pharyngitis, an appropriate macrolide alternative is:
- Azithromycin
- Gentamicin
- Ciprofloxacin
- Fluconazole
Correct Answer: Azithromycin
Q29. Which of the following antibiotics is NOT a macrolide?
- Clarithromycin
- Azithromycin
- Erythromycin
- Clindamycin
Correct Answer: Clindamycin
Q30. The mefA gene confers macrolide resistance primarily by which mechanism and phenotype?
- Target methylation causing high-level cross-resistance (iMLS phenotype)
- Active efflux pump producing low to moderate macrolide resistance (M phenotype)
- Enzymatic drug inactivation with tetracycline co-resistance
- Porin loss leading to broad Gram-negative resistance
Correct Answer: Active efflux pump producing low to moderate macrolide resistance (M phenotype)
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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