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.

In addition, as more water gets pulled into the blood vessels, the concentration of sodium will go down, causing dilutional hyponatremia.

This is especially likely to happen in clients with renal impairment, since they can’t excrete the mannitol, and in heart failure, where the heart can’t handle the increased blood volume.

Other side effects of mannitol are dehydration, hypotension, confusion, headache, nausea and vomiting, which occur due to the rapid fluid shift.Because of these side effects, mannitol is contraindicated in clients with severe hypovolemia, severe renal impairment and anuria; and should be used with caution in clients with edematous conditions, such as heart failure and pulmonary edema.Alright, moving on to carbonic anhydrase inhibitors, which usually end in -zolamide, such as acetazolamide that can be administered orally and intravenously; as well as brinzolamide and dorzolamide, which are administered topically in the eyes, and are actually the most commonly used carbonic anhydrase inhibitors.

Now, as the name suggests, these diuretics inhibit the enzyme carbonic anhydrase, which is found at the apical surface of the tubular cells, facing the tubular lumen.

Long story short, this enzyme catalyzes a reaction where bicarbonate is produced and reabsorbed into the tubular cells. Then, a sodium bicarbonate cotransporter snatches up the bicarbonate and a nearby sodium, and shuttles both into the blood, decreasing their excretion in the urine.

Carbonic anhydrase also increases hydrogen secretion into the tubules to ultimately be excreted. Moreover, this enzyme is also present in the eyes, where it stimulates aqueous humor production.

OK, so once administered, carbonic anhydrase inhibitors bind to the carbonic anhydrase enzymes and inhibit them. Now, acetazolamide acts in the kidneys, where it causes more bicarbonate and sodium to get excreted in the urine, along with water that follows sodium.

However, their diuretic effect is pretty weak, so they are only used as adjunct to other diuretics, or to treat edematous states like pulmonary edema or ascites when there’s also alkalosis, where they will help excrete bicarbonate from the blood to decrease its alkalinity.

In addition, carbonic anhydrase inhibitors are given to clients with cystinuria, where there’s too much cystine in the urine, or gout where there’s too much uric acid in the blood and urine.

The use of carbonic anhydrase inhibitors in these clients raises the pH of the urine, which makes it less favorable for the precipitation of cystine and uric acid crystals, therefore preventing the formation of kidney stones.

Now, on the other hand, brinzolamide and dorzolamide act on carbonic anhydrase enzymes in the eyes. This results in a decreased production of the aqueous humor, which helps lower the intraocular pressure in open-angle glaucoma.

The main side effect of carbonic anhydrase inhibitors is metabolic acidosis, since bicarbonate is lost in the urine. In addition, carbonic anhydrase inhibitors can also cause other electrolyte abnormalities, such as hypokalemia and hyperchloremia; as well as altered blood glucose levels, which can lead to hypo- or hyperglycemia.

This can manifest as neurological side effects like headache, seizures, mental status changes, and paraesthesia. Carbonic anhydrase inhibitors can also cause gastrointestinal side effects, such as altered sense of taste, mostly a bitter or rancid taste, as well as nausea, vomiting, and diarrhea.

Finally, acetazolamide can cause more serious side effects like hepatic necrosis, agranulocytosis, or low blood levels of granulocytes, as well as aplastic anemia, where the bone marrow stops producing all blood cells, leading to pancytopenia.Now, carbonic anhydrase inhibitors are contraindicated in clients with severe renal disease, as well as hepatic diseases like cirrhosis, because these medications can make it harder for the liver to remove ammonia from the blood, which results in hyperammonemia.

In addition, these medications are contraindicated in clients who present with electrolyte abnormalities, such as hyponatremia or hyperkalemia.

Carbonic anhydrase inhibitors should be used with caution in clients with respiratory acidosis, like chronic obstructive pulmonary disease or COPD, in which they exacerbate the underlying acidosis and electrolyte abnormalities.Finally, carbonic anhydrase inhibitors are sulfa medications, so they’re contraindicated in clients with sulfa allergy.Alright, before administering intravenous mannitol to a client with cerebral edema, ensure they have a patent IV and that an indwelling urinary catheter is in place.

Your client could also have an intracranial pressure, or ICP monitor in place as well. Then perform a baseline assessment of your client, including vital signs, lung sounds, SpO2, weight, BUN, creatinine, electrolytes, and blood osmolality or mOsm.

Also review urinalysis results and ensure your client’s urine output is at least 30 to 50 mL/hr. Next, assess your client’s baseline neurological status, including level of consciousness, as well as their current ICP.

Then, check the mannitol solution for the presence of crystals that can sometimes form in the solution. If crystals are present, place the solution in a warm water bath and gently shake it to help the crystals dissolve; then cool the solution to body temperature.

As you set up the IV administration tubing, be sure to use an in-line filter. Lastly, explain to your client that the medication is given to pull water out of brain tissue, which will decrease swelling and relieve pressure, and let them know they should report trouble breathing, headache, blurred vision, or pain at the IV site while the medication is infusing.During administration of mannitol, closely monitor your client’s response to the medication, including decreased ICP, improved level of consciousness, and increased urine output.

Monitor your client closely for signs of fluid overload as fluid from the tissues enters the intravascular space; then monitor for hypovolemia and hypotension as the kidneys work to remove the excess fluid.

Continue to monitor vital signs, lung sounds, SpO2, intake and output, BUN, creatinine, and electrolytes. Also be sure to keep a close eye on the blood sodium and osmolality, and notify the healthcare provider if the blood sodium is more than 150 mEq/L, or if the blood osmolality is more than 320 mOsm.

Lastly, as the medication infuses, continue to monitor your client’s IV site closely for any signs of infiltration. After administration of mannitol, continue to monitor your client’s neurological status, and watch indications of a rebound in their ICP, which can sometimes occur with mannitol administration.Now, if you are caring for a client who has peripheral edema along with metabolic alkalosis, a carbonic anhydrase inhibitor such as IV acetazolamide can be prescribed to help decrease your client’s edema and promote renal elimination of excess bicarbonate and water.

Before administering the medication, ensure your client has a patent IV and obtain a baseline blood gas analysis, CBC, as well as blood glucose, BUN, creatinine, and liver function tests.

Then, explain to your client how the medication will help decrease their edema and correct their metabolic imbalance. During administration, periodically monitor their CBC and blood gas analysis.

If your client has diabetes, keep a close eye on their glucose levels. Finally, monitor for the therapeutic effect of decreased edema and a return to a normal acid-base balance.

Alright, as a quick recap …. Diuretics are medications that act on the kidneys to increase diuresis, or the production of urine, to help excrete more water from the body.

Mannitol is an osmotic diuretic that can be used to lower intraocular and intracranial pressure. It works by increasing osmotic pressure, which pulls water into the intravascular space.

It is freely filtered by the kidneys and eliminated in the urine. Side effects include dilutional hyponatremia, hypovolemia, and dehydration.

Mannitol is contraindicated in severe renal failure and should be used with caution in clients with heart failure or pulmonary edema.

Carbonic anhydrase inhibitors are used to decrease the production of aqueous humor in clients with open-angle glaucoma, or to decrease peripheral edema, especially when there’s also alkalosis.

Side effects include metabolic acidosis, electrolyte imbalance, and altered glucose metabolism. Nursing considerations when administering osmotic diuretics and carbonic anhydrase inhibitors include conducting a thorough baseline assessment, monitoring for side effects, and evaluating the therapeutic response.

When administering mannitol, special attention is focused on ensuring a crystal-free solution and using a filter for administration.

and clients with heart failure, common area Dima. Carbonic anhydrase Inhibitors are used to decrease the production of aqueous humor and clients with open-angle glaucoma or to decrease peripheral edema especially when it's also alkalosis side effects, include metabolic acidosis, electrolyte imbalance and alter glucose metabolism.

Nursing considerations, when administering osmotic diuretics and Carbonic anhydrase. Inhibitors, include conducting a thorough, Baseline assessment, monitoring for side effects and evaluating the therapeutic response.

When administering. Mannitol special attention is focused on ensuring a crystal free solution and using a filter for administration.