Drugs acting on the kidneys 2

Question 1

Are potassium diuretics effective on there own ?

Answer 1

No they have weak diuretic action so are used in combination with loop or thiazide diuretics

Question 2

What is the main reason a potassium sparing diuretic would be used with a loop or thiazide ?

Answer 2

To mainly help reduce K+ excretion

Question 3

What are the 2 main types of potassium sparing diuretics ?

Answer 3

1. Inhibitors of the renal epithelial Na+ channels - Amiloride and Triameterene
2. Aldoesterone antagonists - Spironolactone and Eplereone

Question 4

Describe the action of Amiloride and triameterene

Answer 4

1. They inhibit Na+ channels in the late distal tubule and collecting ducts
2. Due to when Na+ is absorbed K+/H+ is excreted, this will result in decreased K+ loss

Question 5

Describe the mechanism of action of Aldosterone antagonists

Answer 5

1. Competitive antagonists of aldosterone at cytoplasmic aldosterone receptors
2. This decreases the number of Na+/K+ pumps in the basolateral membrane
3. Resulting in decreased Na+ reabsorption and decreased potassium exceretion

Act at the late distal tubules and collecting ducts

Question 6

What are some of the clinical uses of aldosterone antagonists ?

Answer 6

• Moderate to severe CHF
• Secondary hyperaldosteronism
• Primary hyperaldosteronism
• Resistant essential hypertension

Question 7

Describe the mechanism of action of carbonic anhydrase inhibitors

Answer 7

1. Act at the PCT, inhibit carbonic anhydrase
2. Causing increased excretion of HCO3-, Na+, K+ and H20

Question 8

Give some examples of carbonic anhydrase inhibitors and there uses

Answer 8

• Think ‘zolamide’
• Uses e.g. glaucoma, acute mountain sickness

Question 9

What is the main osmotic diuretic

Answer 9

Mannitol

Question 10

Describe the mechanism of action of osmotic diuretics (mannitol)

Answer 10

1. Act in the PCT
2. Essentially raises the concentration of solute in the PCT which helps prevent reabsorption of H20

Question 11

Why is mannitol an ideal diuretic ?

Answer 11

• Pharmacologically inert
• Not metabolised
• Doesn’t enter cells
• Freely filtered at glomerulus
• Undergoes limited reabsorption

Question 12

How is mannitol given ?

Answer 12

IV

Question 13

What are the clinical uses of mannitol ?

Answer 13

• Raised intracranial or intraoculuar pressure
• Prevention of impending acute renal failure