41. Diuretics Flashcards
What is the general action of diuretics?
Explain the various permeabilites along the loop of Henle
What are the 5 classes if diuretic?
Deminish Na+ reabsorption at different sites of nephron. Increase urinary Na+ and water loss.
Descending limb = permeable to water, ascending = permeable to NaCl (active pump)
Carbonic anhydrase inhibitors, loop, thiazide, potassium sparing diuretics, osmotic diuretics
Give an example of a carbonic anhydrase inhibitor.
How does it work?
Carbonic anhydrase main use is not as a diuretic - list 3 other things it is used for
List some SEs of carbonic anhydrase inhibitors
Acetazolamide
Inhibits carbonic anhydrase which usually converts H2CO3 to CO2 and H2O and back to allow it to enter the PCT cell from the lumen (urine), and then converts it back to H+ and HCO3- (bicarbonate is reabsorbed into the blood and H+ is excreted). Thus lose bicarbonate and Na/H exchanger not working so block Na+ reabsorption. Causes acidosis.
Galucoma, epilepsy, mountain sickness (compensates for low O2 -> breathe more -> blow off CO2 -> acidosis)
Metabolic acidosis (contra indicated in significant CKD), sedation, sulphonamide antibiotics (bone marrow suppression)
Give 2 examples of loop diuretics.
How do they work?
Why do people on these often get kidney stones and deafness?
What would you use diuretics to treat?
What are the SEs?
Frusemide, bumetanide
Act mainly on ascending limb of LoH, inhibit Na/K/Cl co-transporter responsible for transporting thse ions from the tubular lumen into the epithelial cell. H2O follows by osmosis. Inhibiting this has a potent diuretic effect. Also causes reduced Ca2+ and Mg2+ absoption across cell. Also causes vasodilation of capacitance veins - imp for heart failure (reduces preload).
Ca2+ remains in filtrate -> lots in urine. Deafness: a similar Na/K/Cl co-transpoter in inner ear - loop diuretics can affect this too
Hypertension, heart failure, volume overload from CKD
Hypokalaemia, hypocalcaemia, dehydration, kidney stones, deafness
List some thiazide and thiazide-like diuretics
How do they work?
What are they used for?
What are some SEs?
Thiazide: bendroflumethiazide, Thiazide-like: chlorthalidone, indapamide, metolazone
Inhibit Na/Cl co-transporter in DCT, preventing Na+ reabsorption and its osmotically associated H2O -> diuresis and initall fall in ECF volume. Overtime RAAs tends to reverse this. Na+ is delived to the cell from the blood via Na/Ca co-transporter, causing increased Ca2+ aborption.
Primarily an antihypertensive. Also can be used for reducing plasma volume and peripheral resistance.
Electrolyte effects (hypokalemia, hypercalcaemia, hyponatraemia), hyperglycaemia (interferes with insulin), hypercholestreolaemia
What are the 2 types of potassium sparing diuretics? Give examples for each.
How do they work?
ENaC antagonists: amiloride, triamterene
Aldosterone antagonists: spironolactone, eplerenone
Amiloride acts on DCT: inhibits Na+ reabsorption (and thus H2O) via ENaC, causing Na+ and H2O excretion and K+ retention. This counteracts K+ losses associated with loop and thiazide therapy. Often used in combinaton
Spironolactone acts on DCT: competitively bind to aldosterone receptors, increasing Na+ and H2O excretion and K+ retention via inhibiting expression of Na/K ATPase channels
What are some clinical uses of amiloride?
What are some SEs of amiloride?
What are some clinical uses of aldosterone inhibitors?
What are some SEs of aldosterone inhibitors?
Heart failure, hypokalaemia (from other diuretics) (so can use combiniation = co-amilofruse, co-amilozide), cirrhosis
Hyperkalaemia, hyponatraemia
Hyperaldosteronism (Conns), heart failure, hypokalaemia (from other diuretics), cirrhosis
HYPERKALAEMIA!!!!! REALLY POTENT HYPERKALAEMICOGENIC AGENT!!! B/c not a blocker - interferes with synthesis instead. Gynecomastia, hyponatraemia (cirrhosis)
What is an osmotic diuretic - how does it work? Give an example.
When might they be used?
What are some SEs?
Any osmotically active molecule that is freely filtered in the glomerulus, and is not reabsorbed by the tubules. In tubular lumen (mainly works in PCT andLoH descending limb), inhibits H2O reabsorption, and inhibits resorption of all solutes (Na+, K+, urea…), molecule drags Na+ from interstital space. E.g. mannitol
Cerebral oedema (dehydrates brain abit, drags fluid out of tissues), oliguric acute renal failure
Transient fluid overload (-> pulmonary oedema), non-pharmacological osmotic diuretics (glucose -> low K and Na, urea)
When should you not give diuretics?
When hypotensive, dehydrated, hypokalaemic (loop/thiazide), hyperkalaemic (amiloride, aldosterone antagonists), post-surgery with poor urine output (leave or give fluid instead)
