Diuretics DSA Flashcards
List the carbonic anhydrase inhibitors
Acetazolamide
Brinzolamide
Dorzolamide
Methazolamide
List the loop diuretics
Bumetanide
Ethacrynic acid
Furosemide (Lasix)
Torsemide
List the thiazide diuretics
Bendroflumethiazide Chlorothiazide Chlorthalidone Hydrochlorothiazide Hydroflumethiazide Indapamide Methyclothiazide Metolazone Polythiazide Trichlormethiazide
List the potassium-sparing diuretics
Mineralocorticoid antagonists (aldosterone antagonists)
- eplerenone
- spironolactone (Aldactone)
Inhibitors of renal sodium channels
- amiloride
- triamterene
List agents that alter water excretion
Osmotic diuretics
- Mannitol
- isosorbide
Antidiuretic hormone antagonists
-conivaptan
What do diuretics do?
Increase sodium excretion and the amount of urine produced by kidney
Used to adjust volume and/or composition of body fluids in a variety of clinical situations: HTN, heart and renal failure, nephrotic syndrome, and cirrhosis)
Compare and contrast diuretic vs natriuretic
Diuretic increases urine volume
-can exert their effects on a variety of targets, such as specific membrane transport proteins, enzymes, and hormone receptors
Natriuretic causes an increase in renal sodium excretion
What are reabsorbed in the proximal tubule?
Sodium bicarbonate (NaHCO3, 85%), NaCl (65% Na), glucose (100%), amino acids (100%) and other organic solutes into blood via specific transport systems in early PCT Potassium (65%) via paracellular pathway Water (65%) passively
What initiates the NaHCO3 reabsorption in the PCT?
Na/H exchanger (NHE3) located in luminal membrane of proximal tubule epithelial ecll
In the PCT, what catalyzes the formation of H2CO3 from CO2 and water?
Membrane-bound and cytoplasmic forms of carbonic anhydrase
What does the Na/K ATPase in the basolateral membrane do in all portions of the nephron?
Pumps reabsorbe Na into interstitium to maintain low intracellular Na concentration
What do acid secretory systems do in the straight segment of the proximal tubule (late proximal tubule)?
Secrete organic acids (uric acid, NSAIDS, diuretics, antibiotics, etc) into the luminal fluid from the blood
Diuretics are delivered to the luminal side of the tubule where most of them act
What is reabsorbed from the thin descending limb of loop of Henle?
Water
Describe reabsorption in the thin ascending limb of loop of Henle
Relatively water impermeable
Impermeable to other ions/solutes
What does the thick ascending limb of loop of Henle reabsorb?
Na (25% of filtered Na)
Impermeable to water
NaCl reabsorption into the interstitial space dilutes the tubular fluid
What is the NaCl transport system in the luminal membrane of the thick ascending loop of Henle?
Na/K/2Cl cotransporter (NKCC2 or NK2CL)
Establishes ion concentration gradient in the interstitium (both renal cortex and medulla)
In the loop of Henle, what does the increase in K concentration in the cells cause?
Causes back diffusion of K into the tubular lumen, allowing a lumen-positive electrical potential to drive reabsorption of cations (Mg2+, Ca2+) via paracellular pathway
Therefore, inhibition of salt transport in the thick limb reduces the lumen-positive potential and causes an increase in urinary excretion of divalent cations in addition to NaCL
Describe reabsorption in the distal convoluted tubule
10% NaCl reabsorbed. Further dilutes tubular fluid
Transported via thiazide-sensitive Na and Cl cotransporter (NCC)
Relatively impermeable to water
Ca2+ is passively reabsorbed by calcium channels (regulated by PTH)
Describe reabsorption and secretion in the collecting tubule (CCT)
Responsible for 2-5% of NaCl reabsorption through epithelial sodium channel (ENaC)
Most important site of K secretion by kidney and site at which virtually all diuretic-induced changes in K balance occur
Where do diuretics act in relation to CCT?
Upstream of CCT
Will increase Na delivery, which will enhance K secretion
Describe the Na/K ATPase pump in CCT
Basolateral. Pumps Na out of cell and into interstitium/blood while pumping K into the cell, where it can exit down the concentration gradient into the lumen/urine
Describe the H-ATPase pump in the CCT
H is secreted by proton pumps into the lumen and increases urine acidity
What does aldosterone do in the CCT?
Increases expression of both ENaC and basolateral Na/K ATPase pumps, leading to increase in Na reabsorption and K secretion, which causes retention of water, increase in blood volume, and increase in blood pressure
What dos antidiuretic hormone (ADH/vasopressin) do in the CCT?
Controls permeability of CCT to water by controlling expression levels of functional aquaporin-2 (AQP2) water channels that insert into the apical membrane
- In absence of ADH, CCT (and collecting duct) is impermeable to water, and dilute urine is produced
- ADH levels are regulated by serum osmolality and volume status
- Alcohol decreases ADH release and increases urine production
What is the protypical carbonic anhydrase (CA) inhibitor?
Acetazolamide
Describe the pharmacokinetics of carbonic anhydrase (CA) inhibitors
Well absorbed following oral administration
Excretion of drug is by secretion in proximal tubule segment (dosing must be reduced in renal in sufficiency)
Excreted drug is unchanged (no hepatic metabolism)
Describe the pharmcodynamics (MOA) of carbonic anhydrase (CA) inhibitors
Cause inhibition of membrane-bound and cytoplasmic forms of carbonic anhydrase, resulting in nearly complete abolition of NaHCO3 reabsorption in proximal tubule (primary site of action)
Describe the results of carbonic anhydrase inhibition
Decreased H formation inside PCT cell, decreased NHE3 activity, increased Na and HCO3 in lumen, and increased diuresis
Up to 45% of whole kidney HCO3 reabsorption is inhibited
Urine pH is increased, and body pH is decreased (increase in urine pH from HCO3 diuresis is apparent within 30 min)
Diuretic efficacy decreases significantly with use over several days (HCO3 depletion leads to enhanced NaCl reabsorption by remainder of nephron, defeating purpose of diuretic action)
As a result of systemic toxicity and eventual NaCl reabsorption, major clinical applications involve targeting CA at other sites other than kidney
Describe the toxicity of carbonic anhydrase (CA) inhibitors
Metabolic acidosis and bicarbonaturia predictably occur from chronic reduction of body HCO3 stores Renal stones can occur because calcium salts are more insoluble as urine pH become more alkaline Potassium wasting (hypokalemia) due to increased Na in CCT, which enhances K secretion (can be counteracted with simultaneous administration of KCl) Drowsiness and paresthesias with large doses Hypersensitivity reactions (fever, rashes, bone marrow suppression due to sulfonamide group) are more rare than above effects