Antimicrobial Therapy Principles Flashcards

A patient with a penicillin allergy requiring treatment for syphilis should receive which alternative?

Answer: Doxycycline

Doxycycline is the recommended alternative for penicillin-allergic patients with syphilis when desensitization is not possible.

Which pharmacokinetic parameter best predicts efficacy of aminoglycoside antibiotics?

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.

A clinician selects empiric broad-spectrum antibiotics for a patient with septic shock. Once culture results return, the appropriate next step is:

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.

Which mechanism underlies MRSA resistance to beta-lactam antibiotics?

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.

A patient develops C. difficile infection after antibiotic therapy. Which drug class most commonly precipitates this complication?

Answer: Fluoroquinolones

Fluoroquinolones, along with clindamycin and broad-spectrum cephalosporins, are among the highest-risk antibiotics for inducing C. difficile infection.

Post-antibiotic effect (PAE) refers to which phenomenon?

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.

Which antibiotic class acts by inhibiting the 30S ribosomal subunit and is effective against intracellular pathogens like Chlamydia?

Answer: Tetracyclines

Tetracyclines bind the 30S ribosomal subunit, inhibiting protein synthesis, and concentrate intracellularly to target organisms like Chlamydia.