GlossaryPharmacokineticsAUC (Area Under Curve)
Pharmacokinetics

AUC (Area Under Curve)

Also known as: area under the curve · total exposure

AUC (area under the curve) is your total exposure to a drug over time: the area under its blood concentration-time curve.

Plot drug concentration in blood against time and AUC is the area under that line, in units such as ng·h/mL. It combines how high levels go and how long they stay there into one number, which is why regulators use it to measure how much drug was absorbed. Several versions exist: AUC0-t runs from dosing to the last measurable sample, AUC0-∞ extrapolates to infinity, and AUC0-τ covers one dosing interval at steady state.

AUC is tied to clearance by a simple relationship: AUC = F × Dose / CL, where F is bioavailability and CL is clearance. For a given bioavailability, clearance is the only parameter that controls overall exposure. So when pharmacokinetics are linear, doubling the dose doubles AUC, and splitting a weekly amount into smaller, more frequent doses leaves weekly AUC unchanged; it changes the shape of the curve (peaks and troughs), not the area.

Why it matters

When you compare two schedules or two products, AUC tells you whether total exposure is the same; Cmax and Cmin tell you how that exposure is spread over time. Comparing compounds by milligrams alone misses differences in both bioavailability and clearance.

Label data let you check the relationship yourself. Semaglutide's label reports an apparent clearance of about 0.05 L/h and a mean steady-state concentration of about 123 ng/mL at 1 mg once weekly. The arithmetic in the example below, using only the clearance and the dose, lands within a few percent of that measured value, which is a useful sanity check on any exposure estimate you build.

How to calculate it

  1. From measured samples, use the trapezoidal rule: for each pair of neighboring time points, average the two concentrations and multiply by the time between them.
  2. Add the slices to get AUC0-t.
  3. To extrapolate to infinity, add the last measured concentration divided by the terminal rate constant (Ct / λz).
  4. At steady state, the average concentration over an interval is AUC0-τ divided by τ.

AUC = F × Dose / CL; Cavg = AUC0-τ / τ; trapezoid slice = (C1 + C2) / 2 × (t2 − t1)

Worked example

Trapezoids with hypothetical samples of 0, 40, 30 and 10 ng/mL at 0, 2, 6 and 12 hours: (0 + 40) / 2 × 2 = 40; (40 + 30) / 2 × 4 = 140; (30 + 10) / 2 × 6 = 120. AUC0-12 = 40 + 140 + 120 = 300 ng·h/mL. Label check for semaglutide: apparent clearance already folds in F, so AUC0-τ = 1 mg ÷ 0.05 L/h = 20 mg·h/L = 20,000 ng·h/mL. Divided by the 168-hour week, Cavg = 20,000 / 168 ≈ 119 ng/mL, close to the label's ~123 ng/mL.

Common mistakes

  • Comparing compounds by milligrams instead of by exposure.
  • Believing that splitting a dose changes total exposure; with linear kinetics it changes peaks and troughs, not weekly AUC.
  • Mixing AUC versions (AUC0-24, AUC0-∞, AUC0-τ) from different studies.
  • Dropping a factor of 1,000 in unit conversions: 1 mg·h/L equals 1,000 ng·h/mL.
  • Reading a large AUC as proof of a large effect; exposure and response are separate questions.

Sources

  1. GuidelineBioavailability Studies Submitted in NDAs or INDs — General Considerations: Guidance for Industry. U.S. Food and Drug Administration (CDER), 2022.
  2. ReviewPlasma clearance. J Vet Pharmacol Ther, 2004. PMID 15601437.
  3. Prescribing informationOZEMPIC (semaglutide) injection, for subcutaneous use: Prescribing Information. Novo Nordisk (FDA-approved labeling), 2026.

Page updated . How we grade evidence: methodology.

Related Terms

Cmax

Cmax is the highest concentration a drug reaches in your blood after a dose; Tmax is how long after the dose that peak occurs.

Cmin

Cmin is the lowest concentration of a drug in your blood during a dosing interval, usually reached just before the next dose (the trough).

Half-Life

Half-life (t½) is the time it takes for the concentration of a drug in your blood plasma to fall by half.

Bioavailability

Bioavailability (F) is the fraction of a dose that reaches your bloodstream as intact drug, compared with the same dose given intravenously.

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