What are Diuretics and How do they Work?

Diuretics

Welcome to this video about diuretics – before we get into the details of diuretics, let’s go over a brief review of the Anatomy & Physiology of the kidney:

– Kidney’s primary function is to regulate the volume, composition, & pH of body fluids
– The normally functioning kidney retains substances needed by the body & eliminates those not needed by way of urine.
– The nephron (pic) is the functional unit of the kidney – each kidney contains approx. 1 million nephrons.
– The nephron is made up of a glomerulus & a tubule.
– The glomerulus being a network of capillaries & the tubule being a structure of epithelial cells that is divided into 3 main segments – the proximal tubule, loop of Henle, & distal tubule – each differing in structure & function.

The nephron has 3 primary functions:

     Glomerular filtration
Tubular reabsorption
Tubular secretion (Last) Urinary excretion

Glomerular filtration is when arterial blood enters the glomerulus at a high pressure & the water, electrolytes, & other solutes are pushed out of the capillaries into the Bowman’s capsule & on to the proximal tubule.

Tubular reabsorption refers to the movement of substances from the tubule to the blood in the peritubular capillaries.

Tubular secretion indicates movement of substances from blood in the peritubular capillaries to glomerular filtrate flowing through the tubules.

DIURETICS are drugs that ↑ the excretion of water, sodium, & other electrolytes through the kidneys, thereby ↑ urine formation & output.
– Diuretics are given to manage edema, heart failure, and hypertension.
– Diuretics act at different sites in the nephron.
– Their job is to ↓ reabsorption of Na+ & water, and to ↑ urine output, therefore often referred to as a “water pill.”

There are 3 main classes of diuretics:

    Thiazide Diuretics
Loop Diuretics
Potassium-sparing Diuretics

There are 2 additional types that are not used as frequently, but I’ll mention briefly:

     Carbonic anhydrase inhibitors
Osmotic Diuretics

Thiazide diuretics
– Most commonly used diuretic
– Hydrochlorothiazide (a.k.a. HCTZ) is the most common thiazide drug used.
– Given for long-term management of heart failure & hypertension.
– They work by ↓ reabsorption of Na+, water, & chloride in the distal convoluted tubule.
– Thiazides are not strong diuretics because most sodium is reabsorbed before it reaches the distal convoluted tubule & only a small amount is reabsorbed at this site.
– Thiazide diuretics are well absorbed & accumulate only in the kidneys.
– Diuretic effect usually begins at 2 hrs & lasts 6-24 hrs.
– Thiazide diuretics are synthetic drugs that are chemically related to the sulfonamides, so they must be used cautiously in patients allergic to sulfonamide drugs.

Loop diuretics
The diuretic of choice when rapid effects are required & when renal function is impaired.

– They inhibit Na+ & Cl- reabsorption in the ascending limb of the loop of Henle (where reabsorption of most filtered Na+ occurs).
– Loop diuretics are the most effective & versatile diuretics available for clinical use.
– Furosemide (Lasix) is the most commonly used loop diuretic
– Furosemide is given for edema & hypertension
– It can be given PO, with dosage gradually increased to obtain adequate diuretic or antihypertensive response.
– If it’s necessary to remove the edema quickly, furosemide may be given by slow IV push. It is also given IVfor acute renal failure & hypertensive crisis.

Potassium-Sparing Diuretics
Act at the distal tubule to ↓ sodium reabsorption & potassium excretion.

– Potassium-sparing diuretics are weak diuretics when used alone, so are usually given in combination with a thiazide like HCTZ that is a potassium-losing diuretic.
– A major adverse effect of these drugs is hyperkalemia (too much potassium) – so patients should not be given potassium supplements, or eat foods high in potassium, or use salt substitutes (which contain KCl rather than NaCl).
Potassium-sparing diuretics include:
Spironolactone – blocks the sodium- retaining effects of aldosterone
Amiloride & Triamterene – both act directly on the distal tubule to ↓ the exchange of sodium for potassium.

Now the 2 not-so-common diuretics I mentioned:
Carbonic anhydrase inhibitors
– The weakest of the diuretics & rarely used in cardiovascular disease.
– Primary use is in the treatment of glaucoma.
Drugs in this class include:

    acetazolamide & methazolamide

Osmotic diuretics
– Inhibit the reabsorption of water & sodium and produce rapid diuresis
– They are given IV
– Common example is Mannitol – useful in treating oliguria or anuria & may prevent acute renal failure during a prolonged surgery or trauma.

Adverse effects of diuretics:
Major adverse effects are fluid & electrolyte imbalances.
– Most frequent problem with thiazide & loop diuretics is hypokalemia (K < 3.5), sometimes requiring treatment with potassium supplements.
– Thiazide & Loop diuretics = hypokalemia

		(K+ level <3.5 mEq/L)

– Potentially serious side effect of potassium-sparing diuretics is hyperkalemia (K > 5), which may lead to cardiac dysrhythmias.
– Potassium-sparing diuretics = hyperkalemia

		(K+ level >5 mEq/L)

Other adverse effects of potassium-losing diuretics (thiazides & loop diuretics) include:

    -Loss of sodium chloride, magnesium, & bicarbonate which also occurs
with diuresis, along with changes in serum & urinary calcium levels.
-Dehydration
-Hyperglycemia
-Elevated serum uric acid
-Ototoxicity (hearing impairment or loss, tinnitus, & dizziness)

Drugs that increase effects of diuretics:

   1. Aminoglycoside antibiotics
2. Antihypertensive drugs
3. Corticosteroids

Drugs that decrease effects of diuretics:

   1.  NSAID’s (ibuprofen, aspirin)
2. Oral contraceptives
3. Vasopressors (epinephrine, norepinephrine)

*Advise patient to tell their doctor they are taking diuretics before starting another medication.

Things to teach your patient:
Reduce sodium intake in the diet to help diuretic drugs be more effective (avoid table salt & obviously salty foods as they may aggravate edema & hypertension).

When taking potassium losing diuretics (HCTZ) the doctor may recommend increasing intake of potassium-containing foods (bananas, OJ) or they may prescribe a potassium supplement.
When on potassium sparing diuretics, do not use salt substitutes, as they contain potassium chloride instead of sodium chloride.
Use protection from sunlight as diuretics cause ↑ sensitivity to the sun.
Do not drink alcohol or take other medications without doctor approval.
Take diuretic early in the day, to decrease nighttime trips to the bathroom.

I’ve covered a lot of information here, so feel free to go back & review. And thank you for watching this video tutorial on DIURETICS.

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by Mometrix Test Preparation | Last Updated: May 8, 2020