Area under the concentration-time profile (AUC) is an important measurement of exposure (see Fig. 1.1). Assessment of AUC tends to be a more "robust" measurement of drug exposure than the measurement of drug concentrations in blood/plasma at a single timepoint. Errors in drug concentration measurements at single timepoints generally have much less impact on AUC.
AUC is expressed as units of concentration x time (e.g., mg x h/mL). Under linear conditions, AUC increases proportionally with dose.
For a reasonable estimation of AUC, collection of plasma/blood samples should occur long enough such that the portion of the AUC that is extrapolated beyond the last measured concentration accounts for <30% of the AUC estimate.
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