2941039
Description
Flashcards by jenny schneider, updated more than 1 year ago
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Created by jenny schneider
over 9 years ago
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| Question | Answer |
| What are three different types of dialysis techniques? | haemodialysis CRRT (haemofiltration) Peritoneal dialysis |
| What is the purpose of dialysis? | Used to remove wastes/toxins from body when kidneys are no longer able to do this |
| Describe haemodialysis | Blood is diverted from body into machine. Blood passes on one side of semipermeable membrane and dialysis fluid is on other side of membrane. Transfer of molecules/solutes between fluids occurs |
| what are the mechanisms by which solutes/drugs may be removed from body during haemodialysis? | diffusion (most common) driven by concentration gradient adsorption to membrane convection - solvent going through membrane drags drug/solute with it (solvent drag) |
| What determines drug dialysability ( the ability of dialysis to remove drug from body?) | MW (small molecules can pass through pores, large molecules cannot) protein binding: highly protein bound will not be removed- only free drug able to cross membraneVd: if drug has large Vd then there is very little drug in blood that can be removed water solubility: dialysate used is aqueous solution, in general drugs with high water solubility will be dialysed to greater extent than lipid soluble drugs plasma clearance: renal clearance is replaced by dialysis clearance; if drug normally undergoes extensive hepatic CL and little renal CL then contribution of CL by dialysis will be small |
| What other factors (besides those relating to the properties of drug and its pharmacokinetics) can influecn how much drug is removed by haemodialysis? | type of dialysis membrane used (there are conventional membranes, high efficiency membranes and high flux membranes - high flux have membrane with larger pores and are more permeable to larger molecules) flow rate of blood and flow rate of dialysate |
| What are two ways we can estimate disalysis CL of a drug? | Method 1: we can measure concentration of drug going in to dialyser and measure concentraiton in blood as it exits the dialyser. Using this we can calculate the extraction ratio ((Cin-Cout)/Cin) and multiply this by blood flow rate to get CL due to dialysis Method 2: we can collect all the watse dialysate fluid and measure a single serum concentration midpoint of the dialysis procedure CLd=excretion rate/Cp where excretion rate = concentration of drug in dialysate x volume of dialyste/time of dialysis |
| How do haemodialysis and heamofiltration (CRRT techniques) differ? | haemodialysis is intermittient- dialysis sessions of a few hours every few days; haemofiltration is continuous 24h per day treatment haemofiltration involves using ultrafiltration where plasma water ir filtered off while haemodialysis uses diffusion across membrane into dialysate fluid on other side |
| Which od the following drugs will be most extensively removed by haemofiltration? (SC=sieving coefficient) pencillin SC=0.68 Diazepam SC=0.02 Cefotaxime SC=1.06 | Cefotaxime as it has the largest sieving coefficient |
| How is peritoneal dialysis performed? | patient has catheter in abdomen and dialysis fluid is placed in the peritoneal cavity. The peritoneal membrane is the membrane in this type of dialysis. Waste (and drug) passes from blood) across the peritoneal membrane into dialysis fluid. The fluid dwells in the peritoneal cavity for a set time and is then drained out. |
| What factors will influence the clearance of drugs from blood by peritoneal dialysis | MW (need to be able to cross membrane) Vd (if large, very little drug in blood to remove) Protein binding (only free drug can cross membrane) dwell time (how long dialysis fluid is left in place) status of peritoneal membrane (inflammation due to infection allows for more exchange in both directions - from blood to fluid and from fluid to bloow |
| True or False: Drug may also be delivered to the body using peritoneal dialysis- by placing drug in the dialysis fluid | True |
| Explain what is happening here | patient who has high levels of lithium in body undergoes haemodialysis (marked by lack line at top). Haemodialysis is removing drug from blood. When HD is ceased, because removal of drug from blood was so rapid, the drug has to re-equilibrate from tissues and we see a rise in lithium blood levels again |
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