Pharmacology Antimicrobial Therapy Principles 2 — Questions and Answers
Question 1: A patient with a penicillin allergy requiring treatment for syphilis should receive which alternative?
- Doxycycline (Correct answer)
- Azithromycin
- Ceftriaxone
- Ciprofloxacin
Correct answer: Doxycycline
Doxycycline is the recommended alternative for penicillin-allergic patients with syphilis when desensitization is not possible.
Question 2: Which pharmacokinetic parameter best predicts efficacy of aminoglycoside antibiotics?
- Time above MIC
- AUC/MIC ratio
- Peak concentration/MIC ratio (Correct answer)
- Trough concentration
Correct answer: Peak concentration/MIC ratio
Aminoglycosides exhibit concentration-dependent killing, so the peak/MIC ratio (Cmax/MIC) is the primary PK/PD predictor of efficacy.
Question 3: A clinician selects empiric broad-spectrum antibiotics for a patient with septic shock. Once culture results return, the appropriate next step is:
- Continue broad-spectrum therapy for 14 days
- De-escalate to the narrowest effective agent (Correct answer)
- Add a second antibiotic for synergy
- Discontinue antibiotics if cultures are negative
Correct answer: De-escalate to the narrowest effective agent
Antibiotic stewardship principles require de-escalation to the narrowest-spectrum agent once culture and sensitivity results are available.
Question 4: Which mechanism underlies MRSA resistance to beta-lactam antibiotics?
- Production of beta-lactamase
- Efflux pump overexpression
- Acquisition of mecA gene encoding altered PBP2a (Correct answer)
- Loss of outer membrane porins
Correct answer: Acquisition of mecA gene encoding altered PBP2a
MRSA carries the mecA gene encoding PBP2a, a penicillin-binding protein with low affinity for all beta-lactam antibiotics.
Question 5: A patient develops C. difficile infection after antibiotic therapy. Which drug class most commonly precipitates this complication?
- Aminoglycosides
- Fluoroquinolones (Correct answer)
- Tetracyclines
- Nitrofurantoin
Correct answer: Fluoroquinolones
Fluoroquinolones, along with clindamycin and broad-spectrum cephalosporins, are among the highest-risk antibiotics for inducing C. difficile infection.
Question 6: Post-antibiotic effect (PAE) refers to which phenomenon?
- Persistent bactericidal activity after serum drug levels fall below MIC (Correct answer)
- Antibiotic accumulation in tissue after dosing ends
- Rebound bacterial growth upon drug discontinuation
- Development of resistance after a short antibiotic course
Correct answer: Persistent bactericidal activity after serum drug levels fall below MIC
PAE is the continued suppression of bacterial growth that persists even after antibiotic concentrations drop below the MIC.
Question 7: Which antibiotic class acts by inhibiting the 30S ribosomal subunit and is effective against intracellular pathogens like Chlamydia?
- Macrolides
- Tetracyclines (Correct answer)
- Fluoroquinolones
- Carbapenems
Correct answer: Tetracyclines
Tetracyclines bind the 30S ribosomal subunit, inhibiting protein synthesis, and concentrate intracellularly to target organisms like Chlamydia.
Pharmacology Antimicrobial Therapy Principles 2
A patient with a penicillin allergy requiring treatment for syphilis should receive which alternative?