Diuretics - Osmotic and carbonic anhydrase inhibitors: Nursing pharmacology

Diuretics, also called water pills, are medications that act on the kidneys to increase diuresis, or the production of urine, to help excrete more water from the body.

Diuretics act on the kidneys’ basic unit, the nephron, to induce salt and water excretion. Zooming into the nephron, it’s made up of a glomerulus, which filters the blood.

The filtered content goes through the renal tubules, which have four parts the proximal convoluted tubule; the U-shaped loop of Henle, with a thin descending, a thin ascending, and a thick ascending limb; and finally, the distal convoluted tubule; and the collecting duct, which drain the urine out of the kidneys.

In this video, we’re going to cover two of the main classes of diuretics, osmotic diuretics and the carbonic anhydrase inhibitors.

Okay, the main osmotic diuretic is mannitol, which is a sugar alcohol that can be administered intravenously. After administration, mannitol travels through the bloodstream and attracts water out of the cells it encounters along the way.

Eventually, mannitol and the extra water reach the kidneys and get secreted by the glomerulus into the renal tubule.

Inside the tubules, mannitol increases the osmolality of the tubular fluid, which makes water stay inside the tubules to be excreted rather than be reabsorbed. Ultimately, both mannitol and water are excreted in the urine.

Osmotic diuretics are primarily used to lower intraocular pressure in glaucoma, or to lower intracranial pressure, such as following head trauma or neurosurgery.

In addition, mannitol can also be used to help excrete harmful substances that may otherwise build up in the body. Examples include myoglobin from the breakdown of muscles, and hemoglobin from the breakdown of red blood cells.

Now, an important side effect is that mannitol also pulls water from cells into the extracellular space, which could worsen edematous conditions like heart failure and pulmonary edema.