Antibiotics – classification and mechanism overview MCQs With Answer

Antibiotics – classification and mechanism overview MCQs With Answer

Antibiotics are vital in pharmacy practice; understanding their classification, mechanisms of action, pharmacodynamics, spectra, and resistance is essential for B.Pharm students. This introduction covers major classes—beta-lactams (penicillins, cephalosporins, carbapenems, monobactams), glycopeptides, macrolides, aminoglycosides, tetracyclines, fluoroquinolones, sulfonamides and trimethoprim—and core mechanisms such as cell wall synthesis inhibition, protein synthesis blockade, nucleic acid synthesis interruption, and folate pathway inhibition. It also highlights time- versus concentration-dependent killing, common adverse effects, and resistance mechanisms like beta-lactamases and efflux pumps. Focus on these keywords to build clinical and pharmacological reasoning. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which class of antibiotics primarily inhibits penicillin-binding proteins (PBPs) and prevents peptidoglycan cross-linking in bacterial cell walls?

• Macrolides (e.g., erythromycin)
• Beta-lactams (e.g., penicillins)
• Aminoglycosides (e.g., gentamicin)
• Fluoroquinolones (e.g., ciprofloxacin)

Correct Answer: Beta-lactams (e.g., penicillins)

Q2. Aminoglycosides exert their bactericidal effect primarily by which mechanism?

• Inhibiting DNA gyrase
• Blocking peptidoglycan synthesis
• Causing misreading of mRNA via 30S ribosomal binding
• Inhibiting dihydropteroate synthase

Correct Answer: Causing misreading of mRNA via 30S ribosomal binding

Q3. Which antibiotic class is best described as time-dependent killers where efficacy correlates with time above MIC (T>MIC)?

• Aminoglycosides
• Fluoroquinolones
• Beta-lactams
• Metronidazole

Correct Answer: Beta-lactams

Q4. Which mechanism explains resistance to beta-lactam antibiotics in many bacteria?

• Target site methylation of 23S rRNA
• Production of beta-lactamase enzymes
• Overexpression of efflux pumps specific for tetracyclines
• Alteration of DNA gyrase

Correct Answer: Production of beta-lactamase enzymes

Q5. Fluoroquinolones primarily inhibit which bacterial enzymes?

• Peptidyl transferase on 50S ribosome
• Dihydrofolate reductase
• DNA gyrase and topoisomerase IV
• Transpeptidases (PBPs)

Correct Answer: DNA gyrase and topoisomerase IV

Q6. Which antibiotic combination synergistically inhibits sequential steps in folate synthesis?

• Penicillin + gentamicin
• Sulfonamide + trimethoprim (co-trimoxazole)
• Vancomycin + ceftriaxone
• Azithromycin + doxycycline

Correct Answer: Sulfonamide + trimethoprim (co-trimoxazole)

Q7. Macrolides inhibit bacterial growth by binding to which ribosomal subunit and interfering with what step?

• 30S; blocking tRNA entry at A site
• 50S; inhibiting translocation (peptidyl transferase center)
• 30S; preventing initiation complex formation
• 50S; cleaving peptidyl-tRNA

Correct Answer: 50S; inhibiting translocation (peptidyl transferase center)

Q8. Vancomycin’s mechanism of action is best described as:

• Inhibition of DNA replication by topoisomerase inhibition
• Binding D-Ala-D-Ala termini to block cell wall polymerization
• Permeabilizing bacterial membranes like polymyxins
• Competitive inhibition of dihydropteroate synthase

Correct Answer: Binding D-Ala-D-Ala termini to block cell wall polymerization

Q9. Which antibiotic is associated with tendon rupture and cartilage damage risk, especially in elderly patients?

• Tetracycline
• Fluoroquinolone (e.g., levofloxacin)
• Macrolide (e.g., erythromycin)
• Sulfonamide (e.g., sulfamethoxazole)

Correct Answer: Fluoroquinolone (e.g., levofloxacin)

Q10. Tetracyclines inhibit bacterial protein synthesis by:

• Binding 50S and blocking peptidyl transfer
• Binding 30S and preventing aminoacyl-tRNA binding to the A site
• Blocking initiation factor IF-2
• Inhibiting formation of 70S ribosome

Correct Answer: Binding 30S and preventing aminoacyl-tRNA binding to the A site

Q11. Which parameter best describes the pharmacodynamic predictor for concentration-dependent antibiotics like aminoglycosides?

• Time above MIC (T>MIC)
• Area under the concentration–time curve (AUC) only
• Peak/MIC (Cmax/MIC)
• Minimum bactericidal concentration (MBC) alone

Correct Answer: Peak/MIC (Cmax/MIC)

Q12. Clindamycin’s major mechanism of resistance among staphylococci and streptococci is due to:

• Mutations in DNA gyrase
• Methylation of 23S rRNA (erm genes)
• Beta-lactamase production
• Porin loss in Gram-negative cell wall

Correct Answer: Methylation of 23S rRNA (erm genes)

Q13. Which antibiotic class is classically considered bacteriostatic rather than bactericidal?

• Penicillins
• Aminoglycosides
• Macrolides and tetracyclines
• Glycopeptides

Correct Answer: Macrolides and tetracyclines

Q14. Which of the following antibiotics requires dose adjustment in renal impairment due to primary renal excretion?

• Doxycycline
• Gentamicin
• Azithromycin
• Clindamycin

Correct Answer: Gentamicin

Q15. A bacterium produces an enzyme that acetylates an antibiotic’s hydroxyl group, rendering it inactive. This is an example of which resistance mechanism?

• Target site alteration
• Enzymatic drug modification
• Reduced permeability via porin loss
• Efflux pump overexpression

Correct Answer: Enzymatic drug modification

Q16. Which antibiotic is known for causing “red man syndrome” if infused too rapidly?

• Vancomycin
• Ceftriaxone
• Linezolid
• Amoxicillin

Correct Answer: Vancomycin

Q17. The primary target of linezolid is:

• DNA gyrase
• 23S rRNA of the 50S ribosomal subunit to block initiation complex
• Peptidoglycan cross-linking enzymes
• Dihydrofolate reductase

Correct Answer: 23S rRNA of the 50S ribosomal subunit to block initiation complex

Q18. Which antibiotic class often causes photosensitivity and permanent tooth discoloration in children?

• Tetracyclines
• Macrolides
• Aminoglycosides
• Glycopeptides

Correct Answer: Tetracyclines

Q19. Which description best fits monobactams like aztreonam?

• Broad Gram-positive coverage including MRSA
• Effective primarily against aerobic Gram-negative rods and resistant to many beta-lactamases
• Mainly used for anaerobic infections
• Folate synthesis inhibitors used orally

Correct Answer: Effective primarily against aerobic Gram-negative rods and resistant to many beta-lactamases

Q20. Which laboratory metric determines the lowest concentration of antibiotic that prevents visible growth of an organism?

• Minimum bactericidal concentration (MBC)
• Minimum inhibitory concentration (MIC)
• Zone of inhibition diameter alone
• Therapeutic index

Correct Answer: Minimum inhibitory concentration (MIC)

Q21. Which antibiotic is contraindicated in pregnancy due to risk of fetal bone and tooth abnormalities?

• Doxycycline
• Amoxicillin
• Penicillin G
• Azithromycin

Correct Answer: Doxycycline

Q22. Efflux pump-mediated resistance commonly reduces intracellular concentration of which antibiotic class?

• Tetracyclines and macrolides
• Beta-lactams only
• Glycopeptides
• Trimethoprim only

Correct Answer: Tetracyclines and macrolides

Q23. Which antibiotic is most associated with Clostridioides difficile overgrowth and severe pseudomembranous colitis?

• Clindamycin
• Gentamicin
• Trimethoprim alone
• Nitrofurantoin

Correct Answer: Clindamycin

Q24. Carbapenems like imipenem are particularly useful clinically because they:

• Are orally active and eliminate Gram-positive cocci only
• Have broad-spectrum activity including many resistant Gram-negative organisms
• Specifically inhibit folate synthesis
• Are first-line for MRSA infections

Correct Answer: Have broad-spectrum activity including many resistant Gram-negative organisms

Q25. Which antibiotic’s dosing strategy uses once-daily high peak dosing to maximize concentration-dependent killing and post-antibiotic effect?

• Aminoglycosides
• Beta-lactams
• Macrolides
• Sulfonamides

Correct Answer: Aminoglycosides

Q26. Mechanism of action of sulfonamides is best described as:

• Inhibition of bacterial DNA gyrase
• Competitive inhibition of dihydropteroate synthase in folate pathway
• Binding to D-Ala-D-Ala to block cell wall synthesis
• Intercalation into DNA causing strand breaks

Correct Answer: Competitive inhibition of dihydropteroate synthase in folate pathway

Q27. Which antibiotic class commonly prolongs the QT interval and can cause torsades de pointes?

• Macrolides and fluoroquinolones
• Beta-lactams
• Tetracyclines
• Glycopeptides

Correct Answer: Macrolides and fluoroquinolones

Q28. A patient with suspected meningitis needs empiric therapy that penetrates CSF well; which antibiotic is commonly used because of good CSF penetration?

• Vancomycin and third-generation cephalosporin (e.g., ceftriaxone)
• Oral amoxicillin alone
• Topical mupirocin
• Gentamicin monotherapy

Correct Answer: Vancomycin and third-generation cephalosporin (e.g., ceftriaxone)

Q29. Which resistance mechanism involves modification of the antibiotic binding site on the ribosome to prevent drug binding?

• Enzymatic degradation of antibiotic
• Target site alteration (e.g., methylation of rRNA)
• Increased renal clearance
• Overproduction of folate pathway enzymes

Correct Answer: Target site alteration (e.g., methylation of rRNA)

Q30. Combination therapy of a beta-lactam with an aminoglycoside is often used because the beta-lactam:

• Blocks renal elimination of the aminoglycoside
• Facilitates aminoglycoside entry by disrupting the cell wall, producing synergy
• Directly inhibits aminoglycoside-modifying enzymes
• Is antagonistic and should be avoided

Correct Answer: Facilitates aminoglycoside entry by disrupting the cell wall, producing synergy

G S Sachin

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.

Mail- Sachin@pharmacyfreak.com