Question

Which class of antibiotics characteristically shows concentration-dependent killing?

• A. Aminoglycosides
• B. Beta-lactams (penicillins)
• C. Glycopeptides (vancomycin)
• D. Macrolides (erythromycin)

Hint:

Higher peak = more kill, plus a long post-antibiotic effect: that means aminoglycosides.

Answer 1

The Correct Option is A

Step 1: Define the pharmacodynamic patterns. Antibacterial killing follows two broad patterns. In concentration-dependent killing, the rate and extent of bacterial kill rise as drug concentration increases well above the MIC; the predictive parameters are peak/MIC (C_max/MIC) and AUC/MIC. In time-dependent killing, kill plateaus once concentration exceeds about 4 x MIC, and efficacy depends on the time above MIC (T>MIC).

Step 2: Classify aminoglycosides. Aminoglycosides (gentamicin, amikacin, tobramycin) are the prototype concentration-dependent bactericidal drugs and also have a prolonged post-antibiotic effect. This is the rationale for once-daily (extended-interval) dosing - a high peak maximises killing while the trough falls low enough to limit nephro- and ototoxicity.

Step 3: Why the others are wrong. Beta-lactams and glycopeptides (vancomycin) are time-dependent; their efficacy depends on T>MIC (vancomycin is best tracked by AUC/MIC but is not concentration-dependent in the aminoglycoside sense). Macrolides are largely time-dependent/bacteriostatic.

Key fact: Aminoglycosides (with fluoroquinolones, metronidazole and daptomycin) are classic concentration-dependent killers, justifying once-daily dosing.