21. CPK OF VANCOMYCIN

Question 1

Describe the difference between AG & vancomycin (VANC)

Answer 1

• AG is concentration-dependent (gram-positive & negative pathogens)
• VANC is time-dependent (gram-positive pathogens)

Question 2

What is the PD target for vancomycin?

Answer 2

AUC 0-24 / MIC

Question 3

What is the target AUC 0-24 / MIC range for vancomycin dosing?

Answer 3

400-600 mg*h/L

assuming MIC of 1ug/mL

Question 4

What is the common LD for vancomycin?

Answer 4

• 20-35 mg/kg
• Preference is 25 mg/kg

Question 5

What is the maximum LD for vancomycin?

Answer 5

3000 mg

Question 6

What is the common MD for vancomycin for pts with normal renal function?

Answer 6

15-20 mg/kg q8-12h
(based on TBW)

Question 7

What is the max infusion rate for vancomycin?

Answer 7

Max infusion rate → 10-15 mg/min

Question 8

How is the dosing interval determined?

Answer 8

dependent on renal function (CrCl)

Question 9

What patients are indicated for a LD of vancomycin?

Answer 9

• Critically-ill or ICU residence
• Requiring dialysis or kidney replacement therapy (KRT)
• Initiating continuous infusion dosing (LD 15-20 mg/kg)

Question 10

Why would a LD be used for vancomycin?

Answer 10

Useful to rapidly achieve targeted serum concentrations & decrease risk of subtherapeutic concentrations during 1st days of treatment

Question 11

What are the 2 potential methods of vancomycin dosing in clinical practice?

Answer 11

1. calculate dose based on m/kg & estimate dosing interval based on CrCl
2. initial dosing using population parameters

Question 12

What are the target Cmax & Cmin for vancomycin when calculating initial dosing based on population parameters?

Answer 12

Cmax 30-35 μg/mL (target ∼ 32.5 μg/mL)
Cmin 10-15 μg/mL (target ∼ 12.5 μg/mL)

Question 13

List the steps of initial vancomycin dosing using population parameters

Answer 13

1. select desired Cmax & Cmin concentrations to achieve the target AUC 0-24 / MIC ratio
2. Calculate correct pt weight
3. Estimate CrCl
4. Calculate the population estimate for k
5. Calculate the population estimate for half-life
6. Calculate the population estimate for volume of distribution (V) using TBW
7. Calculate the population estimate for the dosing interval (tau) & round up to closest practical dosing interval
8. Calculate the maintenance dose (MD), in mg, using the desired Cmax & round to the nearest 250 mg
9. Calculate actual Cmin & Cmax (always double check calculations !)
10. Estimate 24-hour AUC

Question 14

What parameters are used to monitor vancomycin dosing?

Answer 14

24-hour AUC/MIC ratio (400-600)

Trough concentration (>/= 10ug/mL)

Question 15

Explain the 2 methods for monitoring vancomycin dosing

Answer 15

1. Obtain 2 concentrations at or near steady-state (peak concentrations obtained 1-2 hours post-infusion and trough concentration during the same dosing interval), then utilize pharmacokinetic equations to determine AUC and optimize dose
2. Utilize Bayesian software programs embedded with a pharmacokinetic model based on richly sampled vancomycin data as the “Bayesian prior” and obtain 1 or 2 vancomycin concentrations (with at least one trough) - pt does not need to be at steady state

Question 16

When should repeat concentrations be checked for vancomycin dosing?

Answer 16

After dosing changes (depending on duration)
If renal function changes significantly

Question 17

When should once weekly vancomycin concentrations be taken?

Answer 17

for longer courses