Vancomycin Calculator - ClinCalc.com (2024)

This calculator was retired November 2020 and is no longer updated. See the new, updated version of this calculator - now with support for Bayesian modeling.

About This Calculator

This vancomycin calculator uses a variety of published pharmaco*kinetic equations and principles to estimate a vancomycin dosing regimen for a patient. A regimen can be completely empiric, where the vancomycin dose is based on body weight and creatinine clearance, or a regimen may be calculated based on one or more vancomycin levels.

Our vancomycin calculator was specifically designed to help students and clinicians understand the process of calculating a vancomycin regimen. When a vancomycin regimen is calculated, each step in the dosing process is fully enumerated and visible by clicking the "Equations" tab.

In addition to being designed for students, this calculator was also intended with the practicing clinician in mind. All dosing regimens are rounded to the nearest 250 mg with appropriate dosing intervals (eg, Q8hr, Q12hr, Q24hr) to reflect clinical practice. Additionally, after calculating a dosing regimen, a pharmaco*kinetic progress note template is automatically generated for your convenience.

Major Updates to this Calculator

• 2015-06-07 - Drug elimination is accounted for during the infusion time. Read more

• Inappropriate Populations for This Calculator
• Population Estimate of Kel
• Estimate of Kel from a Trough Level
• Population Estimate of Vd
• Actual or Ideal Dosing Body Weight
• Core Pharmaco*kinetic Equations
• Therapeutic Targets: Trough Level
• Therapeutic Targets: AUC:MIC
• Vancomycin Loading Dose

Inappropriate Populations for This Calculator

This calculator is NOT appropriate for the following patient populations or may require a higher degree of clinical judgment:

Population Estimate of Kel

Because vancomycin is primarily renally eliminated, the elimination constant (Kel) is directly related to creatinine clearance (CrCl). While several population estimates exist, this calculator uses the Creighton equation 1 to estimate Kel for a given CrCl using the co*ckcroft-Gault method:2

$$ K_{el} = 0.00083*(CrCl) + 0.0044 $$

Importantly, this method relies on an accurate creatinine clearance; therefore, this method may not be appropriate in patients with unstable renal function or other characteristics that make creatinine clearance difficult to estimate (eg, obesity, elderly, amputations, etc.). Furthermore, it should be emphasized that this is merely an estimate of Kel -- there are many other equations to generate an estimate.

Estimate of Kel from a Trough Level

This calculator can use a single vancomycin trough to estimate true vancomycin clearance (rather than a population estimate from creatinine clearance). This calculator assumes that the vancomycin trough is drawn at steady state, which occurs prior to the fourth vancomycin dose (assuming a consistent dose and dosing regimen).3

Population Estimate of Vd

By default, this calculator suggests a population estimate volume of distribution (Vd) of 0.7 L/kg for vancomycin. There is actually a large variation in the literature, with Vd being described between 0.5 and 1 L/kg.4 There is some evidence that patients with reduced creatinine clearance (CrCl < 60 mL/min) have a larger Vd of 0.83 L/kg, whereas patients with preserved renal function (CrCl ≥ 60 mL/min) have a smaller Vd of 0.57 L/kg.5

Actual or Ideal Dosing Body Weight

Although data are limited, it is recommended that vancomycin be initially dosed on actual body weight (not ideal or adjusted weight), even in obese patients.3 Clinically, this dose may be capped at a specific weight (eg, 120 kg) or dose (eg, 2500 mg), although this practice has not been prospectively studied.

While vancomycin is dosed on actual body weight, it should be noted that creatinine clearance (which may be used to empirically estimate Kel) is based on ideal or adjusted body weight. For more information on the appropriate body weight, see Creatinine Clearance - Adjustments for Obesity.

Core Pharmaco*kinetic Equations

This vancomycin calculator uses three "core" clinical pharmaco*kinetic equations that are well described for intermittent intravenous infusions assuming a one-compartment model.4:

$$ Cp=Cp^0*e^{(-kt)} $$

This equation describes how an initial drug concentration (Cp⁰) declines to a final drug concentration (Cp) over a specified period of time (t) assuming an elimination constant (k).

$$ \Delta C = \frac{Dose}{Vd} $$

This equation describes the change in concentration (ΔC = C_final - C_initial) is related to a given dose and volume of distribution (Vd).

$$ Dose = \frac{C_{peak}*T_{infusion}*Vd*K_{el}*(1-e^{(-K_{el}*Tau)})}{(1-e^{(-K_{el}*T_{infusion})})} $$

This large equation calculates an appropriate drug dose assuming a goal peak drug level (C_peak), volume of distribution (Vd), elimination constant (Kel), dosing frequency (Tau), and infusion time (T_infusion).

Therapeutic Targets: Trough Level

Because an AUC:MIC goal value is difficult to calculate, many clinicians continue to use a goal vancomycin trough level as the therapeutic target of choice. As mentioned in guidelines,3 an AUC of 400 may be achieved with a peak of about 40 mcg/mL and a trough of about 15 mcg/mL. This method is often used as an alternative to direct AUC calculations.

Current guidelines make the following suggestions regarding the optimal vancomycin trough level:3

• All patients should achieve a minimum trough level of > 10 mcg/mL
• Patients with complicated infections should have a goal vancomycin trough of 15 to 20 mcg/mL. Complicated infections include:
  • Pathogen MIC of 1 mcg/mL
  • Bacteremia
  • Endocarditis

  • Osteomyelitis
  • Meningitis
  • Hospital-acquired pneumonia caused by Staph aureus

Therapeutic Targets: AUC:MIC

Although vancomycin has been on the market since the 1950s, there is still considerable controversy regarding the optimal monitoring parameter to maximize efficacy and minimize toxicity. Current guidelines recommend an AUC:MIC ratio of ≥ 400, although this goal is largely based on weak evidence.3^,6^,7^,8

In order for an AUC:MIC ratio to be calculated, both a peak and trough level must be known. Because only trough levels are drawn clinically, a peak level must be estimated. The following equation is used to estimate vancomycin's area under the curve (AUC):5

$$ \\ Lin\;trap = \frac{Trough+Peak}{2}*(T_{infusion}) \\ Log\;trap = \frac{(Peak-Trough)*(Tau-T_{infusion})}{\ln(\frac{Peak}{Trough})} \\ AUC_{0-Tau} = (Lin\;trap) + (Log\;trap) \\ AUC_{0-24} = AUC_{0-Tau}*(24/Tau) = AUC\;in\;mcg*h/mL $$

For more information about AUC:MIC and pharmacodynamic killing, see Vancomycin AUC:MIC versus T>MIC.

Vancomycin Loading Dose

In seriously ill patients, a loading dose of 25-30 mg/kg (actual body weight) may be considered.3 This practice has a theoretical benefit of attaining therapeutic vancomycin levels earlier, but has not been extensively studied. This approach is not supported by evidence from large clinical trials, therefore, the safety and efficacy of a loading dose practice has not been established.

Regardless, based on expert opinion, the following patient populations may be considered for such a loading dose when MRSA is suspected:9

One common question is a maximum vancomycin loading dose. As stated above, there is a lack of evidence supporting loading doses, let alone loading doses in morbidly obese patients. While not recommended by the guidelines, many institutions will "cap" a loading dose at approximately 2000 to 3000 mg. This calculator, when providing a loading dose, will cap at 3000 mg. A vancomycin loading dose cap of 3000 mg represents a maximum weight of 120 kg for a dose of 25 mg/kg.

References and Additional Reading