The highest blood level a drug reaches after a dose—the peak concentration on the drug level curve.Cmax (maximum plasma concentration) is the peak drug concentration achieved after administration. It is determined by the rate and extent of absorption, volume of distribution, and early elimination. For peptide therapeutics, Cmax is clinically relevant in two contexts: efficacy (whether peak concentrations achieve therapeutic receptor occupancy) and safety (whether peak concentrations approach toxic thresholds). The Cmax/MIC ratio is a key efficacy predictor for concentration-dependent antimicrobial peptides.