AUC0t

AUC0-t, or area under the concentration–time curve from time zero to time t, is a pharmacokinetic metric that quantifies drug exposure over a defined period after administration. It represents the total amount of drug that reaches systemic circulation during the interval [0, t].

Calculation and data requirements: AUC0-t is typically computed from measured plasma concentrations at multiple time points using numerical methods such as the trapezoidal rule. If the concentration-time data are C0, C1, ..., Cn at corresponding times t0, t1, ..., tn, the trapezoidal estimate is the sum over i of (C_i + C_{i+1})/2 multiplied by (t_{i+1} − t_i). The value of t is the last sampling time. In some cases, if C0 is not measured, a C0 assumption (often zero) may be used, depending on the drug and study design. Unit choices reflect concentration units and time, commonly ng·h/mL or μg·h/L.

Relation to AUC0-∞: AUC0-∞ estimates total systemic exposure after administration by extending AUC0-t with an extrapolated tail, typically C_t divided by the elimination rate constant (k_el) or using other models. AUC0-∞ is equal to AUC0-t plus the extrapolated portion beyond t.

Applications and limitations: AUC0-t is widely used to compare drug exposure across formulations or dosing regimens, support bioequivalence assessments, and contribute to dose optimization. Its accuracy depends on adequate sampling across the interval and the appropriate handling of data below the limit of quantitation. AUC0-t can be sensitive to sampling times and may be less informative about long-term exposure if t is short.

Overall, AUC0-t provides a practical measure of exposure within a defined time window and complements broader exposure estimates like AUC0-∞.