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.
- Macrolide antibiotics
- Quinupristin/dalfopristin (probably the longest post-antibiotic effect)
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
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:
Theoretically, such drugs might benefit from continuous infusions rather than intermittent doses.