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Vancomycin - Single Level Analysis

Patient:     Location:
Drug:    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 since last dose:   hrs

Important note:  This version was requested because the actual dosing interval may deviate from the medical order (nurse infused dose early/late etc).  The time below should reflect the number of hours since the last dose was given. If the trough level was drawn 12.5 hours after the last dose, enter 12.5.   Note: program will use this as the new dosing interval in order to take into account the extended elimination time.  In the original version the denominator is calculated by subtracting the dosing interval from the time the trough was drawn. 

Desired peak:  mcg/ml   Desired trough:    mcg/ml


A new program was created to determine when to administer the next dose of vancomycin after a supratherapeutic trough is obtained.  An estimated elimination rate constant is generated from the creatinine clearance which is then used to determine the timing of the next dose based on the desired target trough concentration.

I also updated our current trough calculator to also generate an estimated vancomycin kel value based on the creatinine clearance.  Use this program if the vancomcyin level is drawn early and you want to estimate the actual trough just before the next dose to determine if the current regimen is appropriate - link to new program.)


Ambrose-Winter’s Single Trough Method
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.

Side note: the GlobalRPh calculator uses the Vd recommended in Bauer's text: 0.7 L/kg.
    Use the advanced version if you wish to manipulate this value.


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

Alternate expression of kel equation:
single level

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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