Cmax

Cmax, short for maximum plasma concentration, is a pharmacokinetic parameter that represents the highest concentration of a drug observed in the bloodstream after administration. It is derived from the concentration-time profile following dosing and is often reported alongside Tmax, the time required to reach Cmax. Cmax reflects peak systemic exposure and is influenced by dose, route of administration, formulation, absorption rate, distribution, and clearance.

Measurement and interpretation typically involve sampling plasma at multiple time points after dosing and identifying the maximum concentration recorded. Cmax can be affected by factors such as food intake, gastric pH, gastrointestinal motility, drug formulation (immediate vs. extended release), and patient-specific variables like age and organ function. In drug development and regulatory science, Cmax is a key component of bioequivalence studies, where it is often compared between products to ensure similar peak exposure. Regulatory criteria commonly require that Cmax and the total exposure, represented by the area under the curve (AUC), fall within predefined ranges when products are deemed equivalent.

Cmax is related to various pharmacodynamic indices, such as Cmax/MIC for antimicrobials, but it has limitations. A single peak concentration can be sensitive to sampling timing and may not capture total exposure or the drug’s overall effect. Consequently, Cmax is interpreted together with AUC and other factors to guide dose selection, regimen optimization, and assessments of safety and efficacy.