Vancomycin AUC24 calculator from two levels

Estimates the vancomycin AUC over 24 hours from two steady-state levels taken after the same dose, using first-order elimination (Sawchuk-Zaske 1976, Pai 2014). It also gives the elimination rate constant, half-life, peak, trough and, with the dose, volume of distribution and clearance.

Body size and dosing
ASHP/IDSA 2020
Runs on your device

Short answer

The 24-hour vancomycin AUC is estimated from two steady-state levels taken after the same dose, using first-order elimination: k = ln(C1 ÷ C2) ÷ (t2 − t1), with the AUC over one interval scaled to 24 hours (Sawchuk-Zaske 1976; Pai 2014). The 2020 consensus guideline gives a target of 400 to 600 mg·h/L for serious MRSA infection.

Vancomycin AUC from two levels

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Estimate only. Interpret it with the patient's clinical picture and the product label.

Sources

Rybak MJ, Le J, Lodise TP, et al. Therapeutic monitoring of vancomycin for serious methicillin-resistant Staphylococcus aureus infections: a revised consensus guideline and review (ASHP, IDSA, PIDS, SIDP). Am J Health Syst Pharm. 2020;77(11):835–864. DOI 10.1093/ajhp/zxaa036 PubMed 32191793
Pai MP, Neely M, Rodvold KA, Lodise TP. Innovative approaches to optimizing the delivery of vancomycin in individual patients. Adv Drug Deliv Rev. 2014;77:50–57. DOI 10.1016/j.addr.2014.05.016 PubMed 24910345
Sawchuk RJ, Zaske DE. Pharmacokinetics of dosing regimens which utilize multiple intravenous infusions: gentamicin in burn patients. J Pharmacokinet Biopharm. 1976;4(2):183–195. DOI 10.1007/BF01086153 PubMed 950590

Formula version: Vancomycin AUC24 from two levels (first-order, steady state) · MediHelp calc v1.3.1

Formula and sources checked on 2026-11-02

When this estimate is not valid

Assumes steady state (at least the 4th dose with an unchanged regimen, later when the half-life is long, as in kidney impairment) and first-order elimination.
Sample times must be exact: levels well after the infusion (about 1 to 2 hours) and just before the next dose, times counted from the start of the infusion.
Two-level equations are not Bayesian dosing software and ignore the distribution phase and changes in kidney function.
It reports the AUC the levels imply. It does not recommend a dose or an interval.
If kidney function is changing, the estimate is out of date; repeat levels.
The 400 to 600 target is for serious MRSA infection and assumes a vancomycin MIC of 1 mg/L (broth microdilution); with an MIC of 2 mg/L it is usually not reachable safely.

Estimate only. Interpret it with the patient's clinical picture and the product label.

About this calculator

What it is: Estimates the 24-hour vancomycin AUC, half-life and extrapolated peak and trough from two steady-state levels (first-order, one compartment).
Why it is used: The 2020 ASHP/IDSA/PIDS/SIDP guideline recommends AUC-guided dosing (target AUC/MIC 400 to 600) for serious MRSA infection instead of trough-only monitoring.
How to use it: Enter the dosing interval, infusion time, the dose, and two levels with their exact times from the start of the infusion (one 1 to 2 hours after the end of the infusion, one before the next dose), at steady state.
How to read the result: AUC24 of 400 to 600 mg·h/L (assuming MIC 1 mg/L) is the target; below 400 risks failure and above 600 raises nephrotoxicity risk. The result describes the current regimen only; it does not recommend a dose, and it is out of date if kidney function is changing.

How it is calculated

k = ln(C1 ÷ C2) ÷ (t2 − t1)

The elimination rate constant k comes from the two levels (C1 at time t1 and C2 at time t2) and the time between them. All times are counted in hours from the start of the infusion.

Cmax = C1 × e^(k (t1 − tinf)) · Cmin = C2 × e^(−k (τ − t2))

The peak at the end of the infusion and the trough before the next dose are extrapolated from the levels (tinf is the infusion duration and τ the dosing interval).

AUCτ = (Cmin + Cmax) ÷ 2 × tinf + (Cmax − Cmin) ÷ k · AUC24 = AUCτ × 24 ÷ τ

The AUC over one interval is the trapezoid during the infusion plus the elimination part after it. It is scaled to 24 hours.

Vd = (dose ÷ tinf) × (1 − e^(−k × tinf)) ÷ (k × (Cmax − Cmin × e^(−k × tinf))) · CL = k × Vd

If the dose is entered, the calculator also estimates the volume of distribution (Vd) and the clearance.

The AUC24 is compared with the 400 to 600 mg·h/L target for serious MRSA infection from the 2020 consensus guideline (Rybak 2020), which assumes a vancomycin MIC of 1 mg/L. Limits: interval 4–72 h, infusion 0.25–8 h, first level 1–200 mg/L and second level 0.5–200 mg/L, which must be lower than the first and taken after it and no later than the end of the interval.

Worked example

Dosing interval 12 h and infusion 1 h. First level 30 mg/L at 3 h and second level 12 mg/L at 11 h, both counted from the start of the infusion. Dose 1000 mg:

ln(30 ÷ 12) ÷ (11 − 3) = 0.1145 /h
30 × e^(0.1145 × (3 − 1)) = 37.7 mg/L
12 × e^(−0.1145 × (12 − 11)) = 10.7 mg/L
(10.7 + 37.7) ÷ 2 × 1 = 24.2
(37.7 − 10.7) ÷ 0.1145 = 235.9
(24.2 + 235.9) × 24 ÷ 12 = 520 mg·h/L
(1000 ÷ 1) × (1 − e^(−0.1145 × 1)) ÷ (0.1145 × (37.7 − 10.7 × e^(−0.1145 × 1))) = 33.5 L

Estimated AUC24 520 mg·h/L, which is within 400 to 600. Elimination rate constant 0.115 /h, half-life 6.1 h, peak 37.7 mg/L, trough 10.7 mg/L, volume of distribution 33.5 L and clearance 3.8 L/h.

Questions

What conditions does the calculation assume?

Steady state (at least the 4th dose with an unchanged regimen, later when the half-life is long, as in kidney impairment) and first-order elimination.

How exact must the sampling times be?

Exact. Take one level well after the infusion (about 1 to 2 hours) and one just before the next dose, with times counted from the start of the infusion. A first level less than 1 hour after the infusion may still be in the distribution phase and overestimate the AUC.

Does it recommend a dose or an interval?

No. It reports the AUC that the levels imply. Two-level equations are not Bayesian dosing software and ignore the distribution phase and changes in kidney function. If kidney function is changing, repeat levels.

Is the 400 to 600 target always applicable?

The target is for serious MRSA infection and assumes a vancomycin MIC of 1 mg/L (broth microdilution). With an MIC of 2 mg/L it is usually not reachable safely.

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Estimate only. Interpret it with the patient's clinical picture and the product label.