Vancomycin - Single Level Analysis [Advanced version]
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Patient:
Location:
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Drug:
Patient Age (yrs):
? Weight:
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Current dose being given: mg
Current dosing interval: hrs
Current infusion time (hrs):
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Single level drawn - Trough
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Trough level obtained:
mcg/ml
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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]
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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) |
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Background
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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 |
Related pharmacokinetic calculators
Allows the user to estimate the actual (extrapolated) trough based on the elimination rate constant and the number of hours the level was drawn before the next scheduled dose. A
supratherapeutic level may be actually therapeutic if it was drawn just before the next dose.
This new program can be used 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.
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
If you would like to enter the time since the last dose was given, use this version. This new version may be especially useful if the trough was drawn late and thenext dose was
delayed. Example: current regimen vanco 1 gram q12h. Trough wasdrawn 12.5 hours after the last dose.
The GlobalRPh vancomycin single-level calculator uses the Vd recommended in Bauer’s text: 0.7 L/kg. Use the advanced version if you wish to manipulate this value.
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