Diuretics Flashcards
Loop of henle
Out–> 25% Na, K, water, Mg, Ca
In–> nothing
Loop diuretics work here
Proximal convoluted tubule (PCT)
Out –> 40-60% of NaCl, K, Water, HCO3, glucose, amino acids
In –> creatinine, antibiotics, diuretics, Uric acid
Osmotic diuretics & carbonic anhydrase inhibitors work here
Distal convoluted tubule (DCT)
Out–> 15% of Na, Ca, water,
In–> K, H+, urea
In the proximal part –> thiazides and PTH
In the distal part –> osmotic, K-sparing & aldosterone
Collecting duct and tubule
Out–> water
In–> nothing
Osmotic diuretics work here
Loop diuretics (furosemide,bumetanide)
Inhibit the Na/K/2Cl co-transporter in the thick ascending LOH
Prevent Na and K reabsorption causing loss of 15-25% of filtrate–> good for treating fluid salt overload
Can cause low Na,K,Ca,Mg but high urea
When to use Loop diuretics
Fluid or salt overload
Pulmonary oedema, chronic heart failure, renal failure, cirrhosis with ascites, nephrotic syndrome, hypertension if there is renal impairment, acute hypercalcaemia
Side effects of loop diuretics
Can cause low Na,K,Ca,Mg and high urea (gout)
Hypotension & metabolic alkalosis
Ototoxicity with large parenteral doses
Thiazides diuretics (bendroflumethaizide, indapamide, metolazone)
Inhibit Na/Cl cotransporter in the DCT to prevent the reabsorption of Na and Cl but also have a direct vasodilation effect.
Also decreases calcium loss
Used to treat hypertension, chronic heart failure, and can be used to prevent stone formation in idiopathic familial hypercalciuria
Side effects of thiazides
Low Na,K,Mg but high Ca, urea, glucose and lipids
Can be used paradoxically to treat nephrogenic diabetes insipidus
Use with cardiac glycosides is risky because hypercalcaemia will potentiate their action
Potassium sparing diuretics (amiloride, eperenone, triamterene)
Works by blocking apical sodium channels in the late distal tubule to prevent Na reabsorption which reduces K loss from the blood
Alone they have a weak diuretic effect but are added to others to prevent K loss
Uses of K sparing diuretics
Hypertension, heart failure, conn’s syndrome, ascites, LV dysfunction secondary to MI
Add to other diuretics to block potassium loss
Side effects of K sparing diuretics
Low sodium and high potassium
Hypotension
Spirolactone
Aldosterone receptor antagonist
Blocks synthesis of sodium channels and Na/K ATPase
Reduces sodium reabsorption –> slower effect than others
Useful in heart failure but can cause painful gynaecomastia
Diuretics in renal failure
If eGFR is <30ml/min a large dose of loop diuretics is required to regain get same effect as in healthy patients due to nephron hypertropy in the distal tubule
Avoid K-sparing diuretics due to risk of hyperkalaemia and thiazides are of limited use
