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Renal Week 3 > Pharmacokinetics > Flashcards

Flashcards in Pharmacokinetics Deck (26)
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1
Q

Define Bioavailability

A

Fraction of the administered dose that reaches the systemic circulation

2
Q

Define Clearance

A

The amount of plasma cleared of a solute in a given unit of time

3
Q

Define Elimination Rate Constant Ke

A

Fraction of total amount of drug eliminated per unit time

4
Q

Define fe

A

Amount of drug that is renally eliminated

5
Q

Define Volume of Distribution

A

Theoretical volume necessary to account for the total amount of drug if it were present throughout the body at the same concentration as the plasma

6
Q

What is Css?

A

The concentration of a Drug at steady state

7
Q

How many half lives does it take to get a drug to steady state concentration in the plasma?
• what about time needed to eliminate?

A

4-5 half lives - to build to steady state and to eliminate

8
Q

What does it mean if a drug has concentration dependent activity?

A

• It means we need to achieve a target concentration for the drug to be effective, but it doesn’t have to stay there for prolonged periods of time e.g. AMINOGLYCOSIDES

9
Q

Why would you want to just SPACE the dosing interval for aminoglycoside therapy rather than reduce dose and administer at the same intervals?

A

SPACE:
• if you space wider the Troughs you fall below the dangerous plasma concentration

LOWER DOSE:
• if you lower dose then you will either fall below the effective concentration (bad when you’re using a concentration dependent drug)

OR

• you will persistently stay close to the toxic concentration

10
Q

NOTE: Pay attention to things like nausea and vomiting when trying to figure out why a patient’s drug may not be working

A

NOTE: Pay attention to things like nausea and vomiting when trying to figure out why a patient’s drug may not be working

11
Q

What should be an important consideration related to protein loss in patients with kidney disease?

A

Determine if the drug is Protein bound or not

12
Q

How does reduced albumin affect a drug that is protein bound typically?

A

Reduce Albumin:
• Drugs that are protein bound will INCREASE their free/ACTIVE concentration in the serum => this may lead to increased activity

• Unless drug is reliant on protein for appropriate delivery to tissue

13
Q

Before changing up the dosing on a protein bound drug, what should you do?

A

• Use something like the Sheiner-Tozer equation to get an estimate of how much of the drug is FREE

14
Q

Suppose you start administering a drug that is Hepatically eliminated with low fe (kidney excretion) to a patient with good liver function, but days later the patient starts to show signs of toxicity. What is a possible explanation?

A

• Certain drugs like like Moriphine are metabolized by the liver BUT THEN THE METABOLITES are excreted through the kidneys

15
Q

T or F: there is overall less elmination of all protein bound drugs.

A

FALSE, drugs like Penicillin are protein bound but are still excreted extremely efficiently by the proximal tubules.

16
Q

What happens if you give drug X and Y that are both excreted in the renal tubules but drug X is excreted more efficiently?

A

You will OD on drug Y because X will be eliminated from the system at the expense of maintaining levels of Y

17
Q

What are inhibitors of the organic Cation and Anion transporters in the Proximal Tubule?

A

Cation:
• Cimetidine
• Trimethoprim

Anion:
• Probenecid

18
Q

How can pH affect reabsorption?

A

Reabsorption of most drugs is passive, thus Uncharged, Lipophilic molecules are the most readily absorbed

• Changing pH can have huge effects on ADME - SOOOO watch out for acidotic/alkalotic pts. etc.

19
Q

What would the following values for clearance tell you about absorption and secretion of the drug?
• CL = 1.0
•CL greater than 1.0
• CL less than 1.0

A

CL = 1.0 => reabsorption = secretion, or there is neither
CL greater than 1.0 => drug is SECRETED more than absorbed
CL less than 1.0 => drug is ABSORBED more than secreted

20
Q

Cockcroft and Gault formula
• what is it?
•what factors are taken into account with it?

A

C and G
• tells you creatinine clearance
• this is the most frequently used measure of GFR
• takes into account Age, Serum, Creatinine, Gender, and Weight

21
Q

T or F: Formulas used to calculate GFR do so by using lean body wt.

A

False, these formulas use Body Surface Area

22
Q

When should you look at eGFR rather than just Cockcroft and Gault for dosing?

A

Where precision is required for dosing (due to narrow therapeutic or toxic range) and/or estimates may be unreliable (e.g., due to low muscle mass), recommend methods based upon cystatin C or direct measurement of GFR.

23
Q

T or F: eGFR is a good determinant of kidney function in acute kidney disease and dialysis patients.

A

FALSE, use of eGFR in pts. with ACUTE kidney disease and dialysis pts. represents the misuse of eGFR

***DO NOT USE eGFR in pts. with unstable kidney function

24
Q

T or F: in an obese person it is most accurate to use Cockcroft and Gault in evaluation of kidney function.

A

FALSE, function will be false elevate because what you really need to be considering is lean body mass towards inc. creatinine

YOU SHOULD USE WT. or BSA adjusted formulas instead

25
Q

T or F: like in Fat people you should use body wt. or body SA adjusted GFR estimates when dealing with old people too.

A

True

26
Q

When should you do more than just look at serum creatinine to estimate GFR?

A
  • Extremes of age (elderly, children)

* Extremes of body size (obesity, low body mass index, i.e.,