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Tuesday, January 27, 2015

Diuretics: Everything a Nurse Needs to Know

Pharmacology, Drugs, Diuretics, Kidneys, Potassium, Medicine, Renal

Know Your Drugs: The Pharmacology of Diuretics

This post will cover the four classes of diuretics: loop diuretics, thiazide diuretics, potassium-sparring diuretics, and osmotic diuretics. In each class I'll point out the mechanism of action, therapeutic uses, and adverse effects. 

To understand this topic better you might want to check out my posts on:


The kidneys do three basic things:

1) Cleanse extracellular fluid
2) Maintain acid-base balance
3) Excrete metabolic waste. Diuretics mostly effect the maintenance of extracellular fluid (ECF).

Diuretics basically all do the same thing: block sodium and chloride reabsorption. By blocking the reabsorption of these solutes; water is retained in the nephron and that promotes the increase in excretion. Water is going to follow sodium. Very important you understand that. You might want to take a gander at my post on hyponatremia and its role in increasing intracranial pressure.

Loop Diuretics

May also be referred to as High-Ceiling Diuretics, but I mostly see Loop diuretics, so I will refer to them as such. Example: Furosemide (Lasix).

Mechanism of Action: Work to block the reabsorption of sodium and chloride in the Loop of Henle. This is where a lot of wastes are filtered so Loop Diuretics are very effective. Your patient is going to pee a lot... and if they don't, call the doctor.

Can be given orally or through IV. It's given through IV in critical situations such as pulmonary edema. It's metabolized primarily by the liver.

Therapeutic Uses: Loop Diuretics are very powerful, so if a less powerful diuretic can be used, it should be used. You'll give a loop diuretic when:
  • There is pulmonary edema and your patient has a history of congestive heart failure (CHF)
  • Edema around the liver, heart, or kidney and other diuretics haven't been useful
  • Hypertension and other diuretics haven't been useful
Adverse Effects: Think about the mechanism of action of this diuretic and how that can effect the human body.
  • Hyponatremia
  • Hypochloremia
  • Dehydration- Severe dehydration is a major risk. Observe your patient for dehydration status when giving this drug.
  • Hypotension- Again, severe dehydration. Your patient is losing fluid volume.
  • Hypokalemia- This is a huge side effect. You should have orders for labs to watch the potassium serum levels when your patient is getting ANY diuretic. 

Thiazide Diuretics

Thiazides can also be called Benzothiadiazides, but that's too hard for me to say. :) Example: Hydrochlorothiazide (HydroDIURIL).
Mechanism of Action: Thiazides work on the distal convoluted tubule. They are not as potent as Loop Diuretics. They also excrete sodium, chloride, potassium and water but they increase uric acid and glucose. These drugs only work if the patient has adequate kidney function. Loop diuretics are used when kidney function is impaired. 

Therapeutic Uses: 
  • Hypertension
  • Edema (that's mild/moderate)
  • Diabetes Insipidus (can decrease urine production by 30-50%)
Adverse Effects: Basically the same as Loop Diuretics, just probably not as severe.
  • Hyponatremia
  • Hypochloremia
  • Dehydration
  • Hypokalemia

Potassium-Sparring Diuretics

These are more modest in reference to the amount of urine they produce. As the name indicates these also decrease potassium excretion. Examples: 
  • Aldosterone Antagonists: Spironolactone. 
  • Nonaldosterone Antagonists: Triamterene and Amiloride

Mechanism of Action: Spironolactone blocks the actions of aldosterone in the distal nephron. (If you're getting lost, maybe jump to my post on the RAAS system. Seriously, that system is complicated and I don't know many people that feel confident in it. Look at it, read it. Come back to this post afterwards.)

Inhibiting aldosterone retains potassium and excretes sodium. Spironolactone indirectly inhibits aldosterone while Triamterene directly inhibits it. Basically the big take-away is that Triamterene will work faster. Spironolactone takes about 48 hours. You can read more about it, but heck, if you're still with me here, you're in good shape.

Therapeutic uses: These drugs are most likely being used because we are also using a loop or thiazide diuretic and don't want the patient to become hypokalemic.
  • Heart Failure
  • Primary Hyperaldosteronism
  • Premenstrual Syndrome
  • Polycystic Ovary Syndrome
Adverse Effects: 
  • Hyperkalemia- This is the biggest thing to remember. It can produce fatal arrhythmias. I have a whole post dedicated to it. It's most likely to occur if Spironolactone is used by itself and not together with another diuretic. 
  • Endocrine effects- gynecomastia, menstrual irregularities, hirsutism

Osmotic Diuretics

Mannitol (Osmitrol)
is the only osmotic used for diuretic effects. There's more here, but I don't think you need to know it. Not for this post at least.

Mechanism of Action: Mannitol works on the lumen of the nephron by creating osmotic force. It has no significant effect on the excretion of electrolytes. I remembered Mannitol was given to relieve intracranial pressure by thinking: "Mannitol > Manatee > Manatees live in water > Water is on the brain > give Mannitol when there is an excess of water on the brain." I don't know. I'm kind of crazy. Maybe that helps you. Who knows.

Therapeutic Uses:
  • Prevent Renal Failure
  • Reduce Intracranial Pressure (I actually gave Mannitol this week for the first time to treat intracranial pressure. It has to be given through a filter, and you should expect the physician to order a lab to check the patient's osmolality after the infusion is complete.)
  • Reduce Intraocular Pressure
Adverse Effects:
  • Edema- can cause edema anywhere in the body except for the brain. Use in caution with patients with heart disease. 
  • Headache
  • Nausea
  • Vomiting

Ok folks. That's a long post. I hope you made it through to the end.

Go have a cookie. You earned it.

You might also be interested in my other posts on:
Nurse's Guide to Beta Blockers
How to Pass Pharmacology

Let me know if you have any questions by leaving a comment below or sending me an email.




  1. Now i don't think i'll ever forget mannitol! haha
