How do diuretics work?
They act on the kidney to increase excretion of water and sodium chloride, by blocking the reabsorption of electrolytes in the distal tubules.
- They are used to oedema in cirrhosis, CCF and renal disease.
- Thiazides are used to treat hypertension.
- Loop diuretics are powerful top shelf drugs, they have a very rapid onset and short duration of action. They can causes serious electrolyte imbalance and dehydration.
- Potassium-sparing: weak diuretics, usually used with loop or thiazides to prevent hypokalaemia.
Name some thiazide diuretics?
- Metolazone: activity between thiazide & loop.
- Bendroflumethiazide: widely used.
- Mild heart failure and hypertension.
- Bind to & inhibit NaCl synporter in distal tubule.
- Contraindications: gout, NID Diabetes.
- Adverse effects: ↓Na, increases plasma glucose, uric acid and lipids.
Name some Loop diuretics?
- Furosemide: used to reduce peripheral and pulmonary oedema. Unlike thiazides, they are effective in patients with impaired renal function.
- They inhibit the Na/k/2Cl co-transporter in the ascending limb of loop of Henle.
- Diuresis usually occurs about 4hrs after dose.
- Can also be used to treat severe hypercalcaemia.
- Adverse effects: ↓K+ metabolic alkalosis, hypovolaemia, ototoxicity.
Name some potassium-sparing diuretics?
- Spironolactone: blocks aldosterone, used mainly for ascites, Conn's and heart failure.
- Amiloride & triamterene: blocks Na+ channels.
- K-sparing and ACE inhibitors together increase the likelihood of hyperkalaemia.
- Adverse effects: hyperkalaemia, anti-androgen effects such as gynaecomastia esp with spironolactone.