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## Vancomycin - Single Level Analysis [Advanced version]

Patient:     Location:
Drug:
Patient Age (yrs):   ?        Weight:
Current dose being given mg    Current dosing interval: hrs
Current infusion time (hrs):

## Single level drawn - Trough

Trough level obtained:   mcg/ml
When was the trough drawn?:
Enter number of hours before next dose:   hrs
[Hint:   0.01 = <1 minute before next dose.   0.08 = ~5 minutes before next dose]
Desired peak:  mcg/ml   Desired trough:    mcg/ml
Select Vd Method:
Volume of distribution
:   L/kg
Range: 0.5 - 0.95 (Usual: 0.7 L/kg)

## Background

Ambrose-Winter’s Single Trough Method
Principles:
A population Vd is used to estimate the [Peak].
This calculated [Peak] and measured [Trough] are then used to calculate an elimination rate constant (kel).

[Peak]=measured [Trough] + Dose/Vd
kel = ln ([Peak]/[Trough])/Tau
Infusion equations are then used to calculate a new Tau and Dose.

Ambrose-Winter’s volume of distribution equation:
where Vd (L) = (0.17 × [age in years]) + (0.22 × [TBW in kg]) + 15
(Note: TBW even if obese)

#### Reference

Ambrose PJ, Winter ME. In: Winter ME. Basic clinical pharmacokinetics, 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2004:451-76.

Alternate expression of kel equation:

Normally kel = (Ln C1 / C2) / (t2 - t1)
C1= actual or extrapolated Peak; or post peak level
C2= actual or extrapolated trough; or random level
Drawn at least 1.5 x estimated half-life after first level.
(t2 - t1) = Time difference between levels.

Equation 15.5 page 455:
cmax =  [cmin + dose (s) (f)] / Vd

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