Kidney Pharmacology


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  • Created by: Becca
  • Created on: 27-12-13 20:50
Where do osmotic diuretics work? What do they do?
Work on proximal convoluted tubule, highly specific e.g. mannitol used in cerebral oedema (increases osmolality, removes fluid from brain). Inert & freely filtered at Bowman's capsule. Increases osmolality of tubular fluid, decreases H2O reabsorption
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Where do loop diuretics work? What do they do?
Act at Loop of Henle. Very powerful diuretic, cause a large volume of urine to be excreted & cause 15-25% of filtered Na+ to be excreted, NOT reabsorbed
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How do loop diuretics act?
Block Na/2Cl/K symporter of thick AL, decrease availability to concentrate urine (prevents creation of hypertonic interstitium in medulla). Less Na entry into macula densa promotes renin release -> angiotensin II activity -> compensation -> K+ loss
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K+ loss is a complication of using loop diuretics. What else do loop diuretics cause?
Loss of transepithelial potential decreases absorption of cations -> Ca2+/Mg2+ loss (used in hypercalcaemia)
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What conditions are loop diuretics used in?
Chronic heart failure: decrease pulmonary oedema secondary to left ventricular failure & peripheral oedema. Venodilators - rapid effect in acute left ventricular failure. Used in renal failure to improve diuresis
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Where do thiazides work? What do they do? When are they used?
Act on DCT. Inhibit Na/Cl symporter, increase solute in tubular fluid -> decrease H2O reabsorption gradient & circulating volume. 3rd line drugs in hypertension (pts>55yrs) and used in mild-moderate heart failure (vascular & diuretic effects)
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When are thiazides not effective?
Ineffective in moderate renal failure as they are renally excreted/secreted by the weak acid transporter in the PCT prior to acting on DCT
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What are the guidelines/steps when deciding which diuretic to prescribe?
Step 1: A=ACEi (High renin, if 55yrs, black). Step 2: A + C. Step 3: A + C + diuretic. Step 4 (resistance): add alpha blocker/spironolactone/other diuretic -or- beta blocker
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What is hypokalaemia? How do diuretics cause hypokalaemia? What are the major clinical problems?
K+ loss, kaliuresis -> hypokalaemia, 2ndary to loop diuretics/thiazides. Diuretics: decrease Na in ECF, loops block NaCl entry, cause volume depletion, actives RAAS -> Na retention & K loss. Clinical: more -ve membrane potential, cardiac arrhythmias
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What does low body fluid osmolality/blood volume/blood pressure cause & how?
Detected by [NaCl] in macula densa/baroreceptors in afferent arterioles/sympathetic NS (B2-adrenoceptors) -> Renin release -> Increase angiotensin II production & aldosterone release -> Increased Na+ reabsorption & hence increased H2O retention
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Why does alkalosis occur?
Na+ delivery to DCT is similarly associated with H+ loss -> alkalosis
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What are potassium sparing diuretics? Where do they work?
Aldosterone receptor antagonists, work at CD. Na channel blockers - weak diuretics, reduce K loss in combination with K losing agents. ACEIs cause hyperkalaemia & so may negate effects of K-losing diuretics
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How do aldosterone receptor antagonists work? When are they used?
Antagonize aldosterone (mineralocorticoid) receptors. Prevent insertion of Na pumps & channels. Used in primary & secondary hyperaldosteronism (e.g ascites with liver failure), low dose used in CHF to block actions of aldosterone on the heart
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How do sodium channel blockers work?
Block luminal Na channels in DCT & cD. Na+ no longer retained at the expense of K+
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What clinical advice (counselling) should be given to a patient taking diuretics?
Take in morning (large volume urine produced, increased urine flow), avoid excess salt, may cause postural hypotension (especially elderly), thiazides may uncover/worsen diabetes, thiazides may worsen gout, NSAISs may reduce effects of loop diuretics
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Where do loop diuretics work? What do they do?

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Act at Loop of Henle. Very powerful diuretic, cause a large volume of urine to be excreted & cause 15-25% of filtered Na+ to be excreted, NOT reabsorbed

Card 3

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How do loop diuretics act?

Back

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Card 4

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K+ loss is a complication of using loop diuretics. What else do loop diuretics cause?

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Card 5

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What conditions are loop diuretics used in?

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