Renal Clearance Flashcards
Clearance renal
elimination of drugs via the kidneys
In the kidney, drugs are eliminated through:
- filtration
- secretion
- reabsorption
we estimate kidney function through the:
creatinine clearance as a biomarker
Scr means
serum creatinine
fe means
fraction eliminated
clearance
irreversible elimination of a drug from the systemic circulation
it’s not considered clearance if it’s not
made it past systemic circulation
rate of elimination
rate of elimination renal + rate of elimination hepatic
C midpoint
midpoint plasma concentration (where the drug is coming from)
ClR =
rate of urinary excretion / C midpoint
Two methods to determine renal clearance
- Urinary excretion
- fraction of total clearance
Urinary excretion
- over any time interval
- Post-dose: collect urine; collect midpoint concentration
- ClR = C urine * V urine/time all divided by C midpoint
Fraction of total clearance
provides information about the extent of renal elimination
high fe means
ClR»ClH
low fe means
ClR«ClH
fe large or small depends on
ClR relative to Cl
value for the fraction of total renal clearance
0 to 1
Components of Renal Clearance
- glomerular filtration
- secretion via transporters
- reabsorption
glomerular filtration
- movement from glomerular capillary (blood) to renal tubule at Bowman’s capsule
- directly proportional to fu
- depends on fu, GFR, and molecule size (small drug molecules)
- contributes to renal elimination
GFR
- volume of plasma filtered/min
- a measure of kidney function
20 y.o female = 110 ml/min
20 y.o male = 120 ml/min
fu formula
fu = Cu/C
fu: 0 to 1
Cu: concentration unbound
C: total concentration
Renal Secretion via transporters
- active or facilitated transport from blood to the lumen of nephron
- depends on membrane transporters
- highly subjected to drug-drug interactions
- contributes to renal elimination
- blood –> tubules
- depends on substrate
- some drug
renal tubules
network of tiny, tube-like structures in the kidneys responsible for filtering blood and reabsorbing essential substances while eliminating waste products to regulate the body’s fluid and electrolyte balance.
Proximal tubules
responsible for the initial filtration of blood, where they reabsorb essential substances like glucose, amino acids, and ions while also secreting certain waste products into the urine