Diuretics Flashcards
What are diuretics uses for
Chronic heart failure
Hypertension
How do diuretics work
They increase Na+ excretion (natriuresis) which is followed osmotically by water
Where do osmotic agents act
PCT and descending limb
Where do loop diuretics act
Ascending limb
Where do Thiazides act
DCT
Where do K-sparing agents act
Collecting duct
How do osmotic diuretics act
Increase osmolality of tubular fluid in the PCT and loop of Henle and reduces passive reabsorption of H20
What are osmotic diuretics used for
Cerebral oedema
How strong are loop diuretics and how do they act
Very powerful
Block Na+/2Cl-/K+ symporter of the thick ascending limb of the loop of Henle so ions don’t leave the loop of henle which means that less water is reabsorbed into the interstitium
How do loop diuretics affect Na+ and what’s a consequence of this
Increase Na+ delivery to DCT
-Promotes K+ loss which may lead to hypokalaemia
What do loop diuretics do to macula densa cells
Decrease Na+ entry into macula densa
What other conditions are loop diuretics used in and why
Hypercalcaemia
-Reduces absorption of cations and causes loss of Ca2+ and Mg2+
What is the effect of loop diuretics on kidneys after use
Kidney becomes refractory
Uses of loop diuretics
- Chronic heart failure- reduce pulmonary oedema secondary to LVF and peripheral oedema
- Venodilators. Rapid effect in acute LVF
- REnal failure to improve diuresis
What is the mode of action of thiazides
Inhibit active Na+ reabsorption and accompanying Cl-
–>this means there’s increased solute in tubular fluid and so decreases H20 reabsorption gradient
When are thiazides used
Second line drug in hypertension
Mild to moderate heart failure
When are thiazides not useful
IN moderate renal impairment because they’re really excreted by the weak acid transporter in the PCT prior to acting on DCT
Which diuretic is useful in renal failure
Loop diuretics
What is hypokalaemia secondary to
Loop diuretics
Thiazides
How do diuretics cause hypokalaemia
Decrease Na+ in extracellular fluid
loops block Nacl entry to macula densa
Cause volume depletion: which activates the RAAS (Na+ retention and K+ loss)
Whats the problem with hypokalaemia
More negative membrane potential
Cardiac arrhythmias
Reduces activity of Na+ K+ pump- potentiates the action of digoxin
How does alkalosis occur in relation to the DCT
Na+ delivery to the DCT is associated with H+ loss which leads to alkalosis
What is the mode of action of potassium sparing diuretics
Aldosterone receptor antagonists
Na+ channel blockers (weak diuretics but in combination with K+ losing agents may reduce K+ loss)
How to stop hypokalaemia in potassium sparing diuretics
Combine with K+ losing agents
or
Combine with ACEI because they cause hyperkalaemia so may negate the effects of K-losing diuretics
What is the mode of action of aldosterone receptor antagonists
Antagonise aldosterone receptors
-Prevent insertion of Na+ pumps and channels
When are aldosterone receptor antagonists used
primary and secondary hyperaldosteronism (ascites associated with liver failure)
Low dose spironolactone used in CHF to block the actions of aldosterone on the heart
What is the mode of action of sodium channel blockers
Block luminal Na+ channels in late DCT and CD
-Na+ no longer retained at expense of K+
What is a leading cause of chronic renal failure
Diabetes
What drugs appear to slow renal damage
ACE inhibitors
How should diuretics be counselled in practice
- Best taken in morning
- Patients will experience an increase in urine flow
- Patients should avoid excess salt in diet
- May cause postural hypotension (especially in elderly)
- NSAIDs may reduce the effects of loop diuretics
- electrolytes should be monitored
How should thiazides be counselled
May uncover/worsen diabetes
May worsen gout (type of arthritis where crystals form around the joints)
