Download 1-25-17 PPT

Pharmacokinetics
Allie Punke
[email protected]
Aminoglycoside & Vancomycin Dosing
Get your calculators out!
AMG Dosing (without drug
concentrations)
Body Weight/CrCl Application (LD)
Body Weight/CrCl Application (MD)
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 = 0.4 104.5𝑘𝑔 − 63.9𝑘𝑔 + 63.9𝑘𝑔
 𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝐵𝑜𝑑𝑦 𝑊𝑒𝑖𝑔ℎ𝑡 = 80.158 𝑘𝑔
 Step 2: Find LD using nomogram
 LD= 2 mg/kg * 80.158 kg= 160 mg
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
AMG Dosing Using Drug
Concentrations
MEMORIZE!
Estimating MD with concentrations
 1. Find TTR and TPK
Gentamicin 80 mg
Time of infusion=30 minutes
Given Q8H
Target peak is 10 ug/ml
Target trough is 1ug/ml
 TTR = 6.75 hours
 TPK= 1.25 hours
 ∆t= 5.5 hours
Date
Time
Dose #1
1/6
0830
Dose #2
1/6
1700
Dose #3
1/7
0100
TTR
SDC
SDC #1
1/6
2345
2 ug/ml
SDC #2
1/7
0215
4.6 ug/ml
2
23:45
1/6
08:30
1/6
17:00
TPK
4.6
02:15
1/7
01:00
Estimating MD with concentrations

2. Find k
4.6
 𝑘=
ln( 2 )
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
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
Estimating MD with concentrations
 6: Find Dosing Interval
 𝐷𝑜𝑠𝑖𝑛𝑔 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙 = ln
10
1
( )
0.151
 𝐷𝑜𝑠𝑖𝑛𝑔 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙 = 15.7 ℎ
+ 0.5
Estimating MD with concentrations
 7: Find Dose
 𝐷𝑜𝑠𝑒 = 0.5 ℎ ∗ 10 ∗ 0.151 ∗ 21.25 ∗
 𝐷𝑜𝑠𝑒 = 214 𝑚𝑔 𝑞 24ℎ
1−𝑒 −0.151∗24
1−𝑒 −0.151∗0.5
Estimating MD with concentrations
 Double check your calculations-- Predicted Cmax and Cmin
Extended Interval Dosing
Extended Interval Dosing
 Who should this be used in?
 Patients with healthy kidneys
 Who should it not be used in?
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
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

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
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=441.28 mg or 440 mg
 Q36 H
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
Extra Practice
Time Interval—Practice
 1/6 1245 to 1/6 1800
 Step 1: 18-13= 5 hours
 Step 2: 15/60=0.25 hours
 Step 3: 5.25 hours
 1/6 0900 to 1/7 1245
 Step 1: 24-9=15 hours
 Step 2: 15 +12 hours=27
hours
 Step 3: 45minutes/60
minutes=0.75 hours
 Step 4: 27 +0.75 hours=
27.75 hours
Time Interval—Practice
 1/8 1600 to 1/10 2345
 55.75 hours
 1/6 1120 to 1/8 0335
 40.25 hours
Questions?