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

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 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

Estimating MD with concentrations 2. Find k 𝑘= ln⁡( 4.6 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 + 0.5 𝐷𝑜𝑠𝑖𝑛𝑔 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙=15.7 ℎ

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

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 48 hours

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?