Cmax (pharmacology)

Cmax is a term used in pharmacokinetics refers to the maximum (or peak) serum concentration that a drug achieves in a specified compartment or test area of the body after the drug has been administrated and prior to the administration of a second dose. Cmax is the opposite of Cmin, which is the minimum (or trough) concentration that a drug achieves after dosing.

Tmax is the term used in pharmacokinetics to describe the time at which the Cmax is observed.

After an intravenous administration, Cmax and Tmax are closely dependent on the experimental protocol, since the concentrations are always decreasing after the dose. But after oral administration,Cmax and Tmax 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.

Short term drug side effects are most likely to occur at or near the Cmax whereas the therapeutic effect of drug with sustained duration of action usually occurs at concentrations slightly above the Cmin.

The Cmax is often measured in an effort to show bioequivalence between a generic and innovator drug product. According to FDA, drug quality BA (bioavailability) and BE (bioequivalence) rely on pharmacokinetic measures such as AUC and Cmax that are reflective of systemic exposure.