Week 6D Renal Clearance

Question 1

• Drug excretion via kidney is the major route of
elimination of drugs
• Renal drug excretion is the net effect of 3
different processes:

Answer 1

Glomerular filtration (GFR) – a passive process by
which small molecules and drugs are filtered through
the glomerulus of the nephron.
– Active secretion – a carrier-mediated transport
system that requires energy.
– Tubular reabsorption – a passive process that follows
Fick’s law of diffusion or active transport.

Question 2

renal clearance

Answer 2

V of drug contained in plasma removed by kidney per unit time (Ex. L/h).

Question 3

estimation of renal function

Answer 3

Calculation of creatinine clearance

Question 4

drug dosing in renal disease

Answer 4

– Fraction excreted unchanged in urine (feu)

– Fraction of normal renal function

Question 5

renal drug transport

Answer 5

– Tubular secretion
– Tubular reabsorption
– Drug-drug interactions (DDI)

Question 6

Creatinine clearance

caution if:

Answer 6

obese --> BMI = 30-39 use AIBW
morbidly obese --> BMI ³ 40 use LBW
emaciated --> Use ABW, round Crs<1mg/dL
extensive 3rd spacing --> Use estimate of dry weight
changing CrS --> Do not use equation

Question 7

Factors Affecting PK in Renal

Dysfunction

Answer 7

• Fraction of dose excreted unchanged in urine (fe).
• Kidney function
• Dose

Question 8

Fraction of dose excreted unchanged in

urine (fe):

Answer 8

Drugs are eliminated by the kidney to different extents, ranging from 100% (fe=1) to 0% (fe=0).
– fe is determined from CLR relative to CLT.
–Drugs with higher fe (>60%) will require dosage adjustment

Question 9

example
– Drug A, fe = 0.95, Drug B, fe = 0.10
• A 50% reduction in renal clearance will result in
what change in total clearance for these drugs?

Answer 9

0. 95 x 0.5 = 47.5%

0. 10 x 0.5 = 5%

Question 10

greater renal dysfunction =

Answer 10

greater reduction in CLR and CLT)

Question 11

normal creatinine clearance

Answer 11

120 mL/min-70 kg