16 – Diuretics Flashcards
What are the 4 types of diuretic classes?
- Loop diuretics
- Thiazides
- Potassium-sparing diuretics
- Osmotic diuretics (BEST)
What are the sites of Na reabsorption
- Proximal tubule: 60%
- Thick ascending tubule: 25%
- Distal tubule: 7%
- Late distal tubule/collecting duct: 3%
What is the major force for filtration in the nephron?
- Blood pressure
Where is the nephron impermeable to water?
- Thick ascending loop: hypotonic in filtrate
- Distal tubule and collecting duct: permeability is controlled by ADH
What is the main osmotic diuretic?
- Mannitol
Where is the site of action for osmotic diuretics?
- Proximal tubule
- *and entire nephron
o in FILTRATE and exerting osmotic action - VERY LARGE DIURETIC EFFECT
- Use in an emergency
What is the main loop diuretic?
- Furosemide
Where is the site of action for loop diuretics?
- Thick ascending loop of Henle
- 2nd best (used in vet med quite a bit)
- More gradual effects
What is the mechanism of loop diuretics?
- ‘High-ceiling’ diuretics (=large therapeutic effect)
- Inhibit Na/K/2Cl symporter in ASCENDING loop of Henle
- *initially get a mix of natriuretic/kaliuretic effect in ascending limb
- Secondarily: causes Ca and Mg loss in urine
Loop diuretics: initially get a mix of natriuretic/kaliuretic effect in ascending limb leading to…
- Increased volume of NaCl (and K)-enriched fluid to late distal tubule and collecting duct
- Stimulates Na exchange for K in distal tubule and collecting duct
- *end result=strong kaliuretic effect
Kaliuretic definition
- Extra K in urinary filtrate
What is the main thiazide diuretic?
- Hydrochlorothiazide
Where is the site of action for Thiazide diuretics?
- Early portion of distal tubule
- Safer, but less diuresis
What is the mechanism of thiazides?
- Primarily early portion of distal tubule to INHIBIT Na/Cl symporter (natriuresis and diuresis)
o Na exchanged for K in distal tubule and collecting duct
o *less kaliuresis than with furosemide (loop diuretic) - *natriuretic effect TO kaliuretic effect
What is the main potassium-sparing diuretic?
- Spironolactone
Where is the site of action for K-sparing diuretics?
- Late distal tubule and collecting duct
o Usually Na is exchanged for K (body wants to conserve Na and K is excreted) - *prevent Na from being exchanged for K=Na will be lost
What is the mechanism of K-sparing diuretics?
- NOT a transport inhibitor
- Mineralocorticoid (aldosterone) receptor ANTAGONIST
- Minor diuretic effect
- Prevents transcription of Na channel and Na pump genes of late distal tubule and collecting duct=pee out Na instead of K
- *PREVENTS HYPOKALEMIA
- Anti-steroid hormone side effects (limits it’s use)
Since K-sparing diuretics prevent hypokalemia they may be used in combination with
- Other diuretics
Clinical trial of co-treatment of Pimobendan in Doberman DCM
- Seems effective in canine mitral valve failure
Anti-steroid hormone side effects of K-sparing diuretics in males
- Breast growth in males
