Post-antibiotic effect

This is the persistence of antibiotic effect observed long after the serum concentration has fallen below the MIC. It is seen in antibiotics which inhibit some life-sustaining enzyme, or which bind tightly to cell wall components.

The post-antibiotic effect has some relationship to the kill characteristics of the antibiotic, but the relationship is not straightforward. For instance, macrolides are known for time-dependent kill characteristics, but have a strong post-antibiotic effect which probably inhibits bacterial growth rather than causing cell lysis.

Strong post-antibiotic effect

This is mainly seen in drugs which have concentration-dependent kill characteristics.

Such drugs benefit from large intermittent doses; high peak concentrations translate into better post-antibiotic effects.


Moderate post-antibiotic effect

This is seen in drugs which have time-dependent kill characteristics

  • Carbapenems
  • Fluoroquinolones
  • Glycopeptides
  • Linezolid

Weak or absent post-antibiotic effect

This is usually a feature of drugs which act at some critical point in the bacterial reproductive cycle.

The drug must therefore be present in the over-MIC concentration at that critical point.

Such drugs include:

  • β-lactams
  • Cephalosporins
  • Monobactams

Theoretically, such drugs might benefit from continuous infusions rather than intermittent doses.


Oh's Intensive Care Manual: Chapter 72  (pp. 738)  Principles  of  antibiotic  use  by Jeffrey  Lipman

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