Medicine:Cmin

Short description: Minimum blood plasma concentration of a drug during the time between two doses

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. 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:

[math]\displaystyle{ C_{min}= \frac{SFD k_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}}\} }[/math]

[math]\displaystyle{ S }[/math]= Salt factor

[math]\displaystyle{ F }[/math]= Bioavailability

[math]\displaystyle{ D }[/math]= Dose

[math]\displaystyle{ k_\text{e} }[/math]= Elimination rate constant

[math]\displaystyle{ k_a }[/math]= Absorption rate constant

[math]\displaystyle{ V_d }[/math]= Volume of distribution

[math]\displaystyle{ \tau }[/math]= 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.