March 9 - Chronic Kidney Disease II

Question 1

What is hemodialysis?

Answer 1

In hemodialysis, the dialyzer is a semipermeable membrane which filters the blood

Question 2

What is peritoneal dialysis?

Answer 2

In peritoneal dialysis, the peritoneal membrane performs this function

Question 3

What are the issues with drug dosing and dialysis?

Answer 3

Drugs can be removed by these “filters”

Question 4

What are the advantages to peritoneal dialysis?

Answer 4

It can be done at home

It’s less expensive

Question 5

Why would someone not use peritoneal dialysis?

Answer 5

There are certain criteria: you have to have good hand-eye dexterity, you have to be able to work the machine properly (which can be problematic for the elderly), you have to use abdominal membrane so someone who has a lot of abdominal surgery wouldn’t qualify

Question 6

What are the four factors that predict drug removal?

Answer 6

Molecular weight
Protein binding
Volume distribution
Clearance (renal vs nonrenal)

Question 7

How does molecular weight predict drug removal?

Answer 7

Hemodialysis can removed drugs with molecular weight up to 20 000 Da. So drugs less than 20 000 will be removed (e.g., saquinavir, vancomycin) but anything larger than 20 000 Da will not be removed (e.g., iron dextran)..

Question 8

How does protein binding predict drug removal?

Answer 8

Primary drug binding proteins are albumin and alpha-1-glycoprotein. Their molecular weights are 69 000 and 44 100 Da, respectively. So if a drug has a high binding rate (e.g., saquinavir PB = 98%), it won’t easily be removed, however if the binding rate is low (e.g., cefotaxime PB - 13-38%) then it will be removed easier

Question 9

What is volume distribution?

Answer 9

Vd - describes the distribution of drug throughout the body. A small Vd means the drug is distributed primarily in the blood compartment (Vd around 0.2-0.3 L/kg). A large Vd means the drug is distributed widely throughout the tissues and fluids outside of the blood compartment

Question 10

How does volume distribution predict drug removal?

Answer 10

Drugs with large Vd exhibit less dialyzability as compared to those with small Vd; with a large Vd, a drug has a relatively small percentage of drug within the blood and not accessible to the dialyzer

Question 11

How does renal vs nonrenal clearance predict drug removal?

Answer 11

Dialysis replaces renal clearance, so a drug that is excreted via the kidneys will more likely be removed compared to a drug that is extensively metabolized in the liver

Question 12

Why is it important to predict drug removal?

Answer 12

As a pharmacist, we need to know if a drug will easily be removed by dialysis so that we can properly dose and administer at the right time.

Question 13

Is creatinine clearance calculation needed in someone who is receiving dialysis?

Answer 13

No, people receiving dialysis are all considered to have a CrCl < 10 ml/min

Question 14

What provides hemodialysis access?

Answer 14

AV (arteriovenous) fistula, which creates a direct connection between an artery and a vein. This is often done in the lower arm, but can be done in the upper arm as well.
There are also central lines. The advantage is that there is always IV ready to go, and the drugs are more diluted right away within the heart. However there needs to be a large blood flow and least preferred option because it is the most prone to infections

Question 15

Describe the different types of hemodialysis

Answer 15

It’s done 3 time/week in a dialysis centre. There is also nocturnal hemodialysis, which is done 6 times/week at home overnight for 6-8 hours. There’s also short hour daily, which is done 5-6 days/week for 2 hours (this one is more for the fluid abuser, i.e., people drinking more than an litre a day)

Question 16

Describe the different types of peritoneal dialysis

Answer 16

Continuous ambulatory peritoneal dialysis (CAPD); done manually, patient hangs bags with 4-5 exchanges/day, 1 long dwell at night.
Automated peritoneal dialysis (APD); patient hooks up to machine at night and machine does exchanges

Question 17

Hwo does a dialyzer work?

Answer 17

Blood flows through these straws in one direction and dialysate flows in the other direction

Question 18

What are the different ways to remove substances?

Answer 18

Diffusion
Ultrafiltration
Osmosis

Question 19

How does diffusion work in dialysis?

Answer 19

It mostly removes electrolytes. In dialysate, there are specific amounts of certain electrolytes so ensure that electrolytes are removed or replaced via their concentration gradients. Example: patients usually have high amounts of potassium, so the dialysate will have a lot less potassium to ensure its removal. Patients are often acidotic, so dialysate typically has bicarbonate that will enter the blood via diffusion

Question 20

How does ultrafiltration work in dialysis?

Answer 20

Ultrafiltration controls the volume of fluid removed from the patient. Dialysate pressure changes to achieve the prescribed fluid loss. Every patient is prescribed a “dry weight” which is what they should weigh after dialysis

Question 21

How does osmosis work in dialysis?

Answer 21

In dialysis, this refers to water movement across cell membranes in the body (e.g., either from within the red cells to the blood plasma, or from within cells of the various tissues in the body (like muscles) to the interstitial fluid (the fluid in between cells)). “Sodium profiling” can be used to increase the rate of osmosis early in the treatment by increasing the sodium level of the plasma by using a higher sodium level in the dialysate. Both osmosis and ultrafiltration are used to remove the excess fluid from the body

Question 22

What are the three most common causes of chronic kidney disease?

Answer 22

Diabetes is the most common cause (about 50% of CKD patients have diabetes)
Hypertension is the second most common cause
Glomerulonephritis is the third most common cause