AUC Error: One vs. Two Compartment Models

Overview

When assuming a one-compartment model instead of a two-compartment model for vancomycin, the typical calculation error in the Area Under the Curve (AUC) ranges between 8% and 10% underestimation, provided that accurate peak-and-trough data are used. [1] [2]

The Direction of the Error

Underestimation (Peak-Trough Data): When utilizing first-order pharmacokinetic equations (like the Sawchuk-Zaske method) with two steady-state levels (a post-infusion peak and a trough), the one-compartment model completely cuts out the "distribution phase." Because it assumes the drug distributes instantaneously throughout the body, it effectively "chops off" the initial high-concentration curve that occurs right after the infusion finishes, leading to an underestimation of approximately 8%. [2] [3] [4] [5]

Clinical Significance

While a 10% discrepancy exists mathematically, it is generally not considered clinically significant for standard adult populations with stable renal function. For instance, if a true two-compartment model yields a 24-hour AUC of 500 mg·hr/L, a one-compartment calculation might estimate it at roughly 455 mg·hr/L. Both values fall safely within the standard therapeutic target window of 400 to 600 mg·hr/L, meaning the modeling shortcut rarely alters the actual dosing decision. [1] [2]

The Danger Exception: Trough-Only Data

The calculation error changes drastically depending on how the data is handled:

  • The 1-Compartment Model is Resilient: Research demonstrates that a one-compartment model can adequately approximate the true reference AUC using either peak-trough or trough-only data with minimal deviation. [6] [7]
  • The 2-Compartment Model Fails with Sparse Data: If a practitioner tries to force a two-compartment model using trough-only data, the software lacks the necessary mathematical anchors to chart the distribution phase. This causes the two-compartment model to heavily over-extrapolate back to the peak, introducing a massive calculation error that overestimates the AUC by 15.9% to 25.1%. [6]
Summary Comparison
Data Collection Method 1-Compartment Model Error 2-Compartment Model Error Clinical Takeaway
Peak & Trough (Two Levels) ~8% to 10% underestimation Baseline Reference (~0%) Both methods are clinically reliable.
Trough-Only (Single Level) Minimal/acceptable deviation 16% to 25% overestimation Never use a two-compartment model with a single trough sample.
References

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  1. PubMed 31725694 — vancomycin AUC calculation methods.
  2. Optimizing vancomycin therapy: a review of AUC calculation techniques. Contagion Live.
  3. Vancomycin AUC calculation. DoseMe.
  4. Curve enthusiasm: AUC-guided vancomycin dosing & monitoring. ID Stewardship.
  5. Vancomycin AUC estimation methods and their limitations. InsightRX.
  6. Comparison of AUC for vancomycin from one- and two-compartment models using sparse data. PMC8899690.
  7. Comparison of AUC for vancomycin from one- and two-compartment models using sparse data. ResearchGate.