Which antibiotic does not have concentration-dependent killing?

Which antibiotic does not have concentration-dependent killing?

• A. Ceftazidime
• B. Gentamicin
• C. Vancomycin
• D. Doxycycline

Answer: (A)

Understanding how antibiotics kill bacteria relative to drug exposure is the main idea here: some drugs’ efficacy increases with higher peak concentrations or overall exposure (concentration-dependent killing), while others depend on how long the drug level stays above the MIC (time-dependent killing). For concentration-dependent killers, higher Cmax or greater AUC relative to MIC leads to more rapid and extensive bacterial kill. Gentamicin is the classic example of this pattern, so its killing is driven by peak concentrations. Time-dependent killers, on the other hand, rely on staying above the MIC for as much of the dosing interval as possible. Pushing the dose higher doesn’t significantly boost killing unless it prolongs the time above MIC. Ceftazidime, a beta-lactam, is typically described as time-dependent. Vancomycin and doxycycline are also managed with the emphasis on time above MIC or exposure rather than peak concentration. Thus, ceftazidime exemplifies a drug whose killing is not based on achieving high peak concentrations, but rather on maintaining drug levels above the MIC for the dosing interval.

Understanding how antibiotics kill bacteria relative to drug exposure is the main idea here: some drugs’ efficacy increases with higher peak concentrations or overall exposure (concentration-dependent killing), while others depend on how long the drug level stays above the MIC (time-dependent killing).

For concentration-dependent killers, higher Cmax or greater AUC relative to MIC leads to more rapid and extensive bacterial kill. Gentamicin is the classic example of this pattern, so its killing is driven by peak concentrations.

Time-dependent killers, on the other hand, rely on staying above the MIC for as much of the dosing interval as possible. Pushing the dose higher doesn’t significantly boost killing unless it prolongs the time above MIC. Ceftazidime, a beta-lactam, is typically described as time-dependent. Vancomycin and doxycycline are also managed with the emphasis on time above MIC or exposure rather than peak concentration.

Thus, ceftazidime exemplifies a drug whose killing is not based on achieving high peak concentrations, but rather on maintaining drug levels above the MIC for the dosing interval.