1. Allie Punke apunke@uthsc.edu
Pharmacokinetics
Allie Punke

2. Aminoglycoside & Vancomycin Dosing
Get your calculators out!

3. AMG Dosing (without drug concentrations)

4. Body Weight/CrCl Application (LD)

5. Body Weight/CrCl Application (MD)

6. AMG Dosing—without concentrations
A 50 year old woman is admitted to the hospital for a life threatening infection. She weighs 230 pounds and is 5 feet 8 inches. Her SCr is 1.2. The medical team wants to start her on gentamicin. Find her LD and MD
Step 1: Find Adjusted Body Weight
𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝐵𝑜𝑑𝑦 𝑊𝑒𝑖𝑔ℎ𝑡= 𝑘𝑔−63.9𝑘𝑔 +63.9𝑘𝑔
𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝐵𝑜𝑑𝑦 𝑊𝑒𝑖𝑔ℎ𝑡= 𝑘𝑔
Step 2: Find LD using nomogram
LD= 2 mg/kg * kg= 160 mg

7. AMG Dosing—without concentrations
Step 3: Find CrCl using Adjusted Body Weight
𝐶𝑟𝐶𝑙= 140−50 72∗1.2 (80.158kg)(0.85)
Step 4: Find MD using nomogram
𝑀𝐷=0.88∗160=140 𝑚𝑔 𝑄12

8. AMG Dosing Using Drug Concentrations

9. MEMORIZE!

10. Estimating MD with concentrations
1. Find TTR and TPK
TTR = 6.75 hours
TPK= 1.25 hours
∆t= 5.5 hours
Gentamicin 80 mg
Time of infusion=30 minutes
Given Q8H
Target peak is 10 ug/ml
Target trough is 1ug/ml
TTR
Date
Time
SDC
Dose #1
1/6
0830
Dose #2
1700
Dose #3
1/7
0100
SDC #1
2345
2 ug/ml
SDC #2
0215
4.6 ug/ml
TPK 2
23:45
4.6
02:15
1/6
08:30
1/6
17:00
1/7
01:00

11. Estimating MD with concentrations
2. Find k
𝑘= ln⁡( ) 5.5
𝑘=0.151
3. Find Cmax
𝐶𝑚𝑎𝑥= 4.6 𝑒 −0.151(1.25−0.5)
𝐶𝑚𝑎𝑥=5.15
4. Find Cmin
𝐶𝑚𝑖𝑛=5.15∗ 𝑒 −0.151(8−0.5)
𝐶𝑚𝑖𝑛=1.65

12. Estimating MD with concentrations
5: Find Volume
𝑉= 80𝑚𝑔 (1− 𝑒 −0.151∗0.5 ) 0.5∗0.151(5.15−1.65∗ 𝑒 −0.151∗0.5 )
V=21.25 L

13. Estimating MD with concentrations
6: Find Dosing Interval
𝐷𝑜𝑠𝑖𝑛𝑔 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙=ln⁡ ( 10 1 )
𝐷𝑜𝑠𝑖𝑛𝑔 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙=15.7 ℎ

14. Estimating MD with concentrations
7: Find Dose
𝐷𝑜𝑠𝑒=0.5 ℎ∗10∗0.151∗21.25∗ 1− 𝑒 −0.151∗24 1− 𝑒 −0.151∗0.5
𝐷𝑜𝑠𝑒=214 𝑚𝑔 𝑞 24ℎ

15. Estimating MD with concentrations
Double check your calculations-- Predicted Cmax and Cmin

16. Extended Interval Dosing

17. Extended Interval Dosing
Who should this be used in?
Patients with healthy kidneys
Who should it not be used in?

18. Extended Interval Dosing—no drug concentration
Initial dose—Give 7mg/kg over one hour with gentamicin
BW– If >20% of IBW, use adjusted body weight
To find interval of dosing, use GFR

19. Extended Interval Dosing—no drug concentration
Example:
A 24 year old male patient is admitted to the hospital. He weighs 234 pounds and is 5 feet 11 inches. SCr is 1.2. What initial dose of gentamicin should be used in this patient?
Adjusted BW:
87.7 kg
CrCl:
116 ml/min
Dose:
7mg/kg * 87.7 kg=613.9 mg
Q24H

20. Extended Interval Dosing—with a drug concentration
Use a drug concentration obtained 8-14 hours after giving the aminoglycoside to determine the future interval of the drug

21. Extended Interval Dosing—with a drug concentration
MB is admitted to the hospital, and the medical team wants to start gentamicin extended interval dosing for her.
Pt characteristics:
Weight: 79 kg
Height: 5’3”
SCr: 1.5
Age: 56
Step 1: Find Dosing BW
Adjusted=63.04 kg
Step 2: Find CrCl
CrCl=41.6 ml/min
Step 3: Find initial dose
7mg/kg *63.04 kg= mg or 440 mg
Q36 H

22. Extended Interval Dosing—with a drug concentration
Adjust the Dosing Interval Based on Serum Drug Concentration
MB is dosed with gentamicin starting at 1100 on 1/10. A post dose blood sample is collected at 2345 on 1/10. The gentamicin level is 7 ug/ml. What should the dosing interval be?
A. Q24 H
B. Q36H
C. Q48 H
Step 1: Time interval
12.75 hours
Step 2: Use nomogram
48 hours

23. Extra Practice

24. Time Interval—Practice
1/ to 1/6 1800
Step 1: 18-13= 5 hours
Step 2: 15/60=0.25 hours
Step 3: 5.25 hours
1/ to 1/7 1245
Step 1: 24-9=15 hours
Step 2: hours=27 hours
Step 3: 45minutes/60 minutes=0.75 hours
Step 4: hours= hours

25. Time Interval—Practice
1/ to 1/
55.75 hours
1/ to 1/8 0335
40.25 hours

26. Questions?