Excretion

Question 1

Glomerular Filtration

Answer 1

About 10% of renal arterial blood supply gets filtered

􀁺 Normal GFR range is 120-130 mL/min

􀁺 Mild-to-moderate renal impairment is GFR of 30-60 mL/min

􀁺 Severe renal impairment is GFR of 15-30 mL/min

􀁺 Renal failure is GFR

Question 2

Tubular Transport

Answer 2

Tubular transport: modification of glomerular filtrate to
form urine

􀁺 Active transport from urine is very important for Na+, Cl-, HCO3-,glucose, and amino acids, but not for xenobiotics

􀁺 Endocytosis is important for proteins and polypeptides that arefiltered; get reabsorbed by cells in the proximal tubule

􀁺 Passive reabsorption and active secretion are the most
important processes for drugs

Question 3

Tubular Transport : Active Secretion

Answer 3

Active transport from plasma to urine

􀁺 ATP-binding cassette transporters
􀁺 Organic anion secretion; organic acid ionized at physiological pH
􀁺 Organic cation secretion; organic base ionized at physiological
pH

􀁺 These transport systems can “strip” drugs from the proteins they are bound to: as drug is secreted into tubule, more dissociates from protein to maintain equilibrium

Question 4

Tubular Transport: Passive Reabsorption

Answer 4

Passive movement of substances from tubular fluid to blood

􀁺 99% of water is reabsorbed; follows salt passively
􀁺 Lipophilic substances will diffuse back into the blood as their tubule concentration increases

􀁺 Hydrophilic substances remain in the tubule and become more concentrated as water is reabsorbed

􀁺 Weak acids and bases
􀁺 If urine is made more acidic, excretion of weak bases
􀁺 If urine is made more basic, excretion of weak acids

Question 5

Cockcroft-Gault equation

Answer 5

CrCL in mL/min; multiply by 0.85 for females
􀁺 Normal males = 97-137 mL/min
􀁺 Normal females = 88-128 mL/min

􀁺 Used to estimate creatinine clearance in patients with impaired renalfunction so that dosing adjustments can be made for drugs that are mostly or entirely excreted by the kidney