Cmax is the maximum (or peak)serumconcentration that a drug achieves in a specifiedcompartment or test area of the body after the drug has been administered and before the administration of a second dose.[1] It is a standard measurement inpharmacokinetics.
Cmax is the opposite ofCmin, which is the minimum (or trough) concentration that a drug achieves after dosing. The related pharmacokinetic parametertmax is the time at which theCmax is observed.[2]
After an intravenous administration,Cmax andtmax are closely dependent on the experimental protocol, since the concentrations are always decreasing after the dose. But after oral administration,Cmax andtmax are dependent on the extent, and the rate of drug absorption and the disposition profile of the drug. They could be used to characterize the properties of different formulations in the same subject.[3]
Short term drugside effects are most likely to occur at or near theCmax, whereas the therapeutic effect of drug with sustained duration of action usually occurs at concentrations slightly above theCmin.[citation needed]
TheCmax is often measured in an effort to showbioequivalence (BE) between a generic and innovator drug product.[4] According to the FDA, drug qualitybioavailability (BA) and BE rely on pharmacokinetic measurements such asAUC andCmax that are reflective of systemic exposure.[5]