On a concentration-time curve, which metric represents the total amount of drug absorbed systemically?

On a concentration-time curve, which metric represents the total amount of drug absorbed systemically?

• A. Cmax
• B. Tmax
• C. AUC
• D. Half-life

Answer: (C)

The main idea is that the area under the concentration–time curve (AUC) reflects total systemic exposure to the drug. By integrating concentration over all time, AUC captures how much drug has actually entered the bloodstream and how long it stays there. For a given dose and a constant clearance, AUC is proportional to the amount absorbed (often described as F×Dose, where F is bioavailability). So a larger AUC means more drug reached systemic circulation, i.e., a greater total amount absorbed. The other metrics describe different aspects but not total exposure: Cmax is just the peak concentration reached, Tmax is when that peak occurs, and half-life tells you how quickly the drug is eliminated. While these relate to how fast or how high the drug goes in the blood, they do not quantify the overall amount that has entered circulation.

The main idea is that the area under the concentration–time curve (AUC) reflects total systemic exposure to the drug. By integrating concentration over all time, AUC captures how much drug has actually entered the bloodstream and how long it stays there. For a given dose and a constant clearance, AUC is proportional to the amount absorbed (often described as F×Dose, where F is bioavailability). So a larger AUC means more drug reached systemic circulation, i.e., a greater total amount absorbed.

The other metrics describe different aspects but not total exposure: Cmax is just the peak concentration reached, Tmax is when that peak occurs, and half-life tells you how quickly the drug is eliminated. While these relate to how fast or how high the drug goes in the blood, they do not quantify the overall amount that has entered circulation.