C_min

C_min is a term used in pharmacokinetics for the minimum blood plasma concentration reached by a drug prior to administration of a second dose. C_min is the opposite of C_max, the maximum concentration that the drug reaches. C_min must be above certain thresholds, such as the minimum inhibitory concentration (MIC), to achieve a therapeutic effect.

In most cases C_min is directly measurable. At steady state the minimum plasma concentration can also be calculated using the following equation:[1]

${\displaystyle C_{pmin}={\frac {SFDk_{a}}{V_{d}(k_{a}-k)}}\times \{{\frac {e^{-k\tau }}{1-e^{-k\tau }}}-{\frac {e^{-k_{a}\tau }}{1-e^{-k_{a}\tau }}}\}}$

C_min is also an important parameter in bioavailability and bioequivalence studies, it is part of the pharmacokinetic information recommended for submission of investigational new drug applications.[2]

References

1. http://www.pharmpress.com/files/docs/clinical_pharmacokinetics_samplechapter.pdf
2. https://www.fda.gov/downloads/Drugs/.../Guidances/ucm070124.pdf