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PHARMCOKINETICS ALLIE PUNKE DIALYSIS DIALYSIS • T/F: Intermittent dialysis can last hours to days and is used often in critically ill patients. • T/F: Continuous renal replacement compared to intermittent dialysis is characterized by lower blood and dialysate flow rates. • T/F: Diffusion is more useful than convection at removing drugs with a large molecular weight. DIALYSIS • T/F: Vancomycin is removed by hemodialysis. • T/F: During CVVH, the dialysate runs at about 10-40 ml/min. DIALYSIS • Be able to recognize the characteristics of a drug that make it more or less likely to be removed by dialysis. • Drug-Specific Factors: • 1. ↑ Molecular Weight= • 2. ↑ Protein Binding= • 3. ↑ Volume of distribution= DIALYSIS • Process-Specific Factors: • 1. ↑ Membrane pore size= • 2. ↑ Membrane Surface Area= • 3. ↑ KUF coefficient= • 4. ↑ Blood flow= • 5. ↑ Dialysate flow= • 6. ↑ Dialysis time= DIALYSIS • Will this drug be likely to removed by dialysis? • 1. MW=1200 Daltons, 89% protein bound, Vd= 2 L/kg • 2. MW=400 Daltons, 40% protein bound, Vd=0.23 L/kg • 3. A patient has received a toxic dose of a medication with the following drug characteristics (MW=1300 Daltons, 92% protein bound, Vd= 2.4 L/kg). The team wants the patient to receive dialysis to increase the elimination of the drug. What do you think about this recommendation? GET YOUR CALCULATORS OUT! DIALYSIS AB is a 65 kg woman receiving HD on Monday, Wednesday, and Friday from 8-1pm. For a possible infection, she was admitted to the hospital and received her first dose of Vancomycin on Saturday (Day 1) and the second dose on Monday (Day 3) at 4pm. Vancomycin plasma concentrations: Day 3 @ 7 PM: 39 mg/L Day 5 @ 8 AM: 23 mg/L Day 5 @ 1 PM: 11 mg/L 1. Calculate AB’s interdialytic CL and the intradialytic CL of Vanc. (Vd of Vanc is 0.8). DIALYSIS 2. What fraction of Vanc is eliminated by HD? 3. What supplemental dose of vanc should be given to reach a target concentration of 40 mg/L? DIALYSIS • 4. Because the concentration was drawn immediately following dialysis, will this likely underestimate or overestimate CL? Explain your answer. DIALYSIS DIALYSIS • Calculating dialysis CL can be done using: • 1. Flow Model Method • Remember that: • 2. Dialysate Recovery Method • Pro/cons: DIALYSIS • During a 3 hour dialysis session, the dialysate flow was 500 ml/min, and the blood flow rate was 300 ml/min. Pt’s hematocrit was 33%. The following Vancomycin concentrations are available: • 60 minutes: Ca=43 mg/L, Cv= 37 • 120 minutes: Ca=40 mg/L, Cv= 36, CDialysate= 3.5 mg/L, Volume collected (from 0 to 120 minutes= 38 L) • 180 minutes: Ca=38mg/L, Cv= 34 • Calculate CLD using the dialysate recovery method DIALYSIS • Calculate CLD using data at 120 minutes and the flow model method. CONTINUOUS THERAPIES CONTINUOUS THERAPIES • 1. CVVH • CL= • 2. CVVHD • CL= • 3. CVVHDF • CL= CONTINUOUS THERAPIES • A patient is receiving CVVHDF. UFR= 1.8 L/h, dialysate flow= 40 ml/min, and blood flow rate=175 ml/min. Calculate the estimate CL of a drug that is 60% protein bound by the CVVHDF. PERITONEAL DIALYSIS PERITONEAL DIALYSIS • What are some differences that need to be accounted for when a patient is undergoing peritoneal dialysis? PERITONEAL DIALYSIS Which graph represents a one time dose of antibiotics? Be able to explain these graphs! QUESTIONS? GOOD LUCK!