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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 Dosingβwithout concentrations ο 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 ο Step 1: Find Adjusted Body Weight ο π΄πππ’π π‘ππ π΅πππ¦ ππππβπ‘ = 0.4 104.5ππ β 63.9ππ + 63.9ππ ο π΄πππ’π π‘ππ π΅πππ¦ ππππβπ‘ = 80.158 ππ ο Step 2: Find LD using nomogram ο LD= 2 mg/kg * 80.158 kg= 160 mg AMG Dosingβwithout concentrations ο Step 3: Find CrCl using Adjusted Body Weight ο πΆππΆπ = 140β50 72β1.2 (80.158kg)(0.85) ο Step 4: Find MD using nomogram ο ππ· = 0.88 β 160 = 140 ππ π12 AMG Dosing Using Drug Concentrations MEMORIZE! Estimating MD with concentrations ο 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 ο TTR = 6.75 hours ο TPK= 1.25 hours ο βt= 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 ο 2. Find k 4.6 ο π= ln( 2 ) 5.5 ο π = 0.151 ο 3. Find Cmax ο πΆπππ₯ = 4.6 π β0.151(1.25β0.5) ο πΆπππ₯ = 5.15 ο 4. Find Cmin ο πΆπππ = 5.15 β π β0.151(8β0.5) ο πΆπππ = 1.65 Estimating MD with concentrations ο 5: Find Volume οπ= 80ππ (1βπ β0.151β0.5 ) 0.5β0.151(5.15β1.65βπ β0.151β0.5 ) ο V=21.25 L Estimating MD with concentrations ο 6: Find Dosing Interval ο π·ππ πππ πππ‘πππ£ππ = ln 10 1 ( ) 0.151 ο π·ππ πππ πππ‘πππ£ππ = 15.7 β + 0.5 Estimating MD with concentrations ο 7: Find Dose ο π·ππ π = 0.5 β β 10 β 0.151 β 21.25 β ο π·ππ π = 214 ππ π 24β 1βπ β0.151β24 1βπ β0.151β0.5 Estimating MD with concentrations ο Double check your calculations-- Predicted Cmax and Cmin Extended Interval Dosing Extended Interval Dosing ο Who should this be used in? ο Patients with healthy kidneys ο Who should it not be used in? Extended Interval Dosingβno drug concentration ο Initial doseβGive 7mg/kg over one hour with gentamicin ο BWβ If >20% of IBW, use adjusted body weight ο To find interval of dosing, use GFR Extended Interval Dosingβno drug concentration ο Example: ο 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? ο Adjusted BW: 87.7 kg ο CrCl: ο 116 ml/min ο Dose: ο 7mg/kg * 87.7 kg=613.9 mg ο Q24H ο Extended Interval Dosingβwith a drug concentration ο Use a drug concentration obtained 8-14 hours after giving the aminoglycoside to determine the future interval of the drug Extended Interval Dosingβwith a drug concentration ο MB is admitted to the hospital, and the medical team wants to start gentamicin extended interval dosing for her. ο Pt characteristics: ο Weight: 79 kg ο Height: 5β3β ο SCr: 1.5 ο Age: 56 ο Step 1: Find Dosing BW ο Adjusted=63.04 kg ο Step 2: Find CrCl ο CrCl=41.6 ml/min ο Step 3: Find initial dose ο 7mg/kg *63.04 kg=441.28 mg or 440 mg ο Q36 H Extended Interval Dosingβwith a drug concentration ο Adjust the Dosing Interval Based on Serum Drug Concentration ο 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? ο A. Q24 H ο B. Q36H ο C. Q48 H ο Step 1: Time interval ο 12.75 hours ο Step 2: Use nomogram Extra Practice Time IntervalβPractice ο 1/6 1245 to 1/6 1800 ο Step 1: 18-13= 5 hours ο Step 2: 15/60=0.25 hours ο Step 3: 5.25 hours ο 1/6 0900 to 1/7 1245 ο Step 1: 24-9=15 hours ο Step 2: 15 +12 hours=27 hours ο Step 3: 45minutes/60 minutes=0.75 hours ο Step 4: 27 +0.75 hours= 27.75 hours Time IntervalβPractice ο 1/8 1600 to 1/10 2345 ο 55.75 hours ο 1/6 1120 to 1/8 0335 ο 40.25 hours Questions?