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
Outlier (Kel) model (calculates Kel)
kel = CrCl x 0.0008
Normal (CL) model (calculates CL)
CL = (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 (CpTmax/CpTmin)]
where:
tinf = infusion time
CpTmin = Target trough
CpTmax = Target peak
iv. Calculate ideal maintenance dose
MD = kel x Vd x CpTmax x tinf x (1 - e-kel x tau / 1 - e-kel x tinf)
v. User selects practical dosage and interval
vi. Calculate expected steady-state peak & trough levels
CpSSmax = [MD / (tinf x Vd x kel)] x [(1 - e-kel x tinf) / 1-e-kel x tau)]
CpSSmin = CpSSmax * 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.
5. User selects practical dosage and interval
6. Calculate expected peak & trough levels
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:
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: