Vancomycin formulas

 

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Because there are situations where a 1- or 2-compartment model may be more appropriate, both models are included in Kinetics.  In general, if you are giving small doses (6mg/kg) more frequently, per the Lake and Peterson method, then the 2-compartment model may be more appropriate.  If you are administering larger 15-20mg/kg doses over extended dosing intervals, per older dosing methods, then the 1-compartment model may be more appropriate.

 

The vancomycin models are not hard-coded into the program.  The parameters are found in the drug model database and are fully user-editable.  You can tailor each drug model to fit your patient population, or you can create your own models.  See the Edit drug models section of the help file for further information.

 

Initial dosing 1-compartment population model

 

1.   Determine maintenance dose (MD)

 

i.   Calculate volume of distribution (Vd)

Vd = 0.7 x TBW

where:

TBW = total body weight in kg

 

ii.   Calculate elimination rate (kel) from creatinine clearance

 

Outl (outlier/Kel) model (calculates Kel)

kel = CrCl x 0.0008

 

Norm (normal/CL) model (calculates CL)

kel = (CrCl x 0.065) / Vd

where CrCl =  creatinine clearance

 

Adjust CL to IBW model

CL =  [Nonrenal + (NormCrCl x  Renal)] x (AdjBW/TBW)

where:

NormCrCl = normalized creatinine clearance

Nonrenal = 0

Renal = 0.065

AdjBW = LBW + (0.4 * (TBW-LBW))

LBW = lean body weight in kg

TBW = total body weight in kg

 

iii.  Calculate ideal dosing interval (tau)

 

tau = tinf + [ (-1 / kel) x ln (Cpmax/Cpmin)]

where:

tinf = infusion time

Cpmin = Target trough

Cpmax = Target peak

 

iv.   Calculate ideal maintenance dose

 

MD = kel  x  Vd  x  Cpmax  x  tinf  x  (1 - e-kel x tau / 1 - e-kel x tinf)

 

v.  User selects practical dosage and interval

 

vi.  Calculate expected peak & trough levels        

 

Peak = [MD / (tinf x Vd x kel)] x [(1 - e-kel x tinf) / 1-e-kel x tau)]

 

Trough =   Peak * e -kel x (tau- tinf)

 

 

Initial dosing 2 compartment population model

 

1.  Calculate dosing weight (DW)

 DW = LBW + [ (ABW - LBW) x CF ]

         where"

ABW = actual weight

CF is a correction factor for obesity: 40%

 

2.  Calculate clearance (CL) from creatinine clearance

 CL =  0.17 + (CrCl x 0.06)

         where CrCl =  creatinine clearance

 

3.   Calculate ideal dosing interval (tau)

tau = 6 x (72 / [ {10 * CL} + 1.9] )

 where CL = vancomycin clearance

 

 

4.   Calculate ideal maintenance dose

The target trough level drives the dose.

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5.    User selects practical dosage and interval

 

6.    Calculate expected peak & trough levels

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Adjust dose 1-compartment model

 

The methodology utilized is the same as that for aminoglycosides.

 

 

Adjust dose 2-compartment model

 

1.   Minimize Bayesian function

 

The Bayesian method uses population-derived pharmacokinetic parameters (ie., Vd and CL) as a starting point and then adjusts those parameters based on the serum level results taking into consideration the variability of the population-derived parameters and the variability of the drug assay procedure. To achieve that end, the least squares method based on the Bayesian algorithm estimates the parameters CL and Vd which minimize the following function:

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2.   Calculate ideal dosing interval

Same equation as initial dosing.

 

3.   Calculate ideal maintenance dose

Same equation as initial dosing, using Bayesian-derived Vd and kel.

 

4.   User selects practical dosage and interval

 

5.   Calculate expected peak & trough levels

Same equation as initial dosing.

 


See also:

Introduction

Monitoring parameters

Precautions

Bibliography

 

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