What Is PK (Pharmacokinetic) Related Terminologies?

Here are main PK (Pharmacokinetic) related terminologies as shown in this FDA picture:

Drug Concentration - Drug Concentration is usally measured as the amount of the drug in a unit of blood volumn.

C_max (maximum concentration) - C_max is the highest concentration of drug in the blood that is measured after the drug is taken.

T_max - T_max is the time to reach the C_max after the drug is taken.

C_min (minimum concentration) - C_min is the lowest concentration of drug in the blood that is measured after the drug is taken.

If the drug is taken as a single dose, the C_min should be closed to zero.

If the drug is taken as a repeated dose, the C_min should be the drug concentration right before the next dose.

C_min is also called "Trough".

AUC (Area Under the Curve) - AUC is the area under the curve of the drug concentration over time. AUC represents the overall amount of drug in the bloodstream after a dose.

Since drug concentrations are measured with some time intervals, not continuously, The AUC is usually calculated with an approximation that simulates the actual the drug concentration curve.

t½ (Half Life) - t½ is the amount of time it takes for the drug concentration in the blood to decline by half. The half-life is among the most important PK measurements for how often a drug has to be dosed (once-a-day or twice-a-day, etc).

SS (Steady State) - SS means that a person has been on a drug for enough time (usually one to two weeks) so that the drug concentration is not building up in the bloodstream anymore.

MTC (Minimum Toxic Concentration) - MTC is the lowest concentration of drug in the blood that toxicity usually occurs.

MEC (Minimum Effective Concentration) - MEC is the lowest concentration of drug in the blood that is required for drug effect.

TW (Therapeutic Window) - TW is the range of drug concentration between the MEC (Minimum Effective Concentration) and the MTC (Minimum Toxic Concentration).

TI (Therapeutic Index) - TI refers to several indices that are used for measuring a drug's safety. Higher TI means a safer drug. Lower TI means a dangerous drug. Two examples of TI are:

• TI = MTC/MEC - The ratio of MTC (Minimum Toxic Concentration) against MEC (Minimum Effective Concentration).
• TI = TD50/ED50 - The ratio of TD50 (the dose of drug that causes a toxic response in 50% of the population) again ED50 (the dose of drug that is therapeutically effective in 50% of the population).

 

⇒ What Is Drug ADME

⇐ What Is PK-PD Relation

⇑ PK/PD Basic Concepts

⇑⇑ PK/PD Tutorials