C_min is a term used in pharmacokinetics for the minimum blood plasma concentration reached by a drug during a dosing interval, which is the time interval between administration of two doses. This definition is slightly different from C_trough, the concentration immediately prior to administration of the next dose.^[1] 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.^[2]

In most cases C_min is directly measurable. At steady state the minimum plasma concentration can also be calculated using the following equation:^[3]

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

${\displaystyle S}$= Salt factor

${\displaystyle F}$= Bioavailability

${\displaystyle D}$= Dose

${\displaystyle k_{\text{e}}}$= Elimination rate constant

${\displaystyle k_{a}}$= Absorption rate constant

${\displaystyle V_{d}}$= Volume of distribution

${\displaystyle \tau }$= Dosing interval

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.^[4]

References