The highest concentration reached in the compartment of reference, usually plasma (see Cmax and plasma concentration), divided by the MIC.

Cmax/MIC is a PK/PD index that integrates PK (Cmax) and PD (MIC as a measure of potency).

If Cmax/MIC correlates best with outcome, a drug exhibits a concentration-dependent pattern of activity (e.g, the aminoglycosides, the fluoroquinolones, daptomycin, colistin, metronidazole). The amount of the drug rather than the dosing frequency determines the clinical efficacy. fCmax/MIC refers to the unbound fraction of the drug.