How potassium sparing diuretics work?
Thiazides, loop diuretics and potassium-sparing diuretics all work on the kidneys. The kidneys have a network of tubes that make urine by filtering the blood in two stages. In the first stage, the water, salt and the waste products such as urea are filtered out from the blood, leaving behind the red and white blood cells. But lots of nutrients and other essential substances also leave the blood at this stage. In the second stage there is a backwards filter, where the kidneys re-absorb the nutrients and essential substances back into the blood. This leaves the waste products, plus some salt and water, in the kidneys. This waste leaves the kidneys as urine. Heart failure makes the kidneys re-absorb more water and salt into the blood, and so produce less urine. This is the body’s way of trying to compensate for the reduced pumping power of the heart, but it actually makes matters worse. There is a bigger volume of blood for the heart to pump, and so more work for it to do. Also the excess
