Pharmacology Diuretics

Loop Diuretics

Loop diuretics act on the loop of Henle. They inhibit chloride transport of sodium into the circulation. Loop diuretics cause rapid diuresis, which decreases cardiac output and blood pressure.

Administration of Thiazides

Orally Diuresis usually starts within 2 hours of administration. It is important to avoid diuretics at night to minimize nocturia. If thiazide diuretics are needed twice daily, dosing times are often scheduled at 8 a.m. and 2 p.m. to minimize sleep interruption. Thiazide diuretics are often used as an adjunct to loop diuretics. Hydrochlorothiazide has not been shown to have any ill effects on humans and can be used safely during pregnancy.PO adult dosage of hydrochlorothiazide is 12.5 to 25 mg/day.

Spironolactone

Potassium-sparing diuretics The onset of spironolactone is 24 to 48 hours, with peak effects occurring in 48 to 72 hours. Terminal half-life is 10 to 35 hours. Total duration is unknown

Contraindications of Potassium-sparring diuretics

Potassium-sparing diuretics are contraindicated for patients with hyperkalemia, severe renal failure, or anuria. Spironolactone is not recommended for use in pregnancy. Spironolactone carries a black box warning for secondary malignancy.

Side effects of potassium-sparring diuretics

Spironolactone can cause endocrine side effects such as menstrual irregularities, hirsutism, impotence, and gynecomastia. The most significant adverse effect of the potassium-sparing agents is hyperkalemia.

Drug interactions with potassium-sparring diuretics

There is a significant risk for hyperkalemia if potassium-sparing diuretics are taken in conjunction with potassium supplements or angiotensin-converting enzyme (ACE) inhibitors. Potassium-sparing diuretics enhance the action of lithium, and lithium toxicity can occur. NSAIDs can decrease the diuretic effect when taken with potassium-sparing diuretics.

Thiazide diuretics

Thiazides act on the distal convoluted renal tubule, past the loop of Henle, and, like loop diuretics, they promote sodium, chloride, and water excretion. The difference between loop diuretics and thiazide diuretics is the degree to which the drugs promote diuresis. Diuresis is lower with thiazide diuretics than with loop diuretics. Thiazides cause vasodilation by directly acting on the arterioles to lower blood pressure. Thiazide diuretics also promote sodium chloride and water excretion. This results in a decrease in intravascular volume, which lowers cardiac output and blood pressure.

Hydrochlorothiazide

thiazide diuretic The half-life of hydrochlorothiazide is 6 to 15 hours, which is longer in comparison to loop diuretics. Onset occurs in 2 hours with peak effects occurring in 4 to 6 hours and duration up to 12 hours.

Drug interactions with thiazides

As with loop diuretics, a serious drug interaction can occur with digoxin. Thiazides can cause hypokalemia. Hypokalemia potentiates the action of digoxin. Digoxin toxicity can occur in the presence of hypokalemia and potentiated digoxin action. Thiazides enhance the action of lithium, and lithium toxicity can occur. Thiazides can decrease the effectiveness of some antidiabetic drugs, causing increased blood glucose levels. Thiazides also interact with antihypertensive drugs.

Contraindications of thiazides

Contraindications for thiazide diuretics include known allergy, hepatic coma, anuria, and renal failure. Thiazides are also contraindicated for use in chronic kidney disease. Symptoms of severe kidney impairment include oliguria (marked decrease in urine output), elevated blood urea nitrogen (BUN), and elevated serum creatinine.

The nurse is caring for a patient who is hypotensive after receiving a dose of furosemide. Which action of furosemide can cause hypotension? Tubular reabsorption of sodium and chloride Water retention and potassium-sparing Excess fluid loss and dehydration Decreased blood volume and cardiac output

Decreased blood volume and cardiac output

Summary of Diuretics

Diuretics are a class of drug that is used to treat hypertension and HF. There are three classes of diuretics: loop, thiazide, and potassium-sparing. Each class of diuretics works at a different point in the renal tubule. Diuretics treat peripheral edema and pulmonary edema. Depending on the condition, diuretics of different potency are used. Loop diuretics are high in potency and can cause severe dehydration. Because diuretics cause diuresis, these drugs affect electrolyte balance, fluid balance, and blood pressure. Diuretics are associated with risks and potential adverse effects. The effects of diuretics can be direct, such as reduction in blood pressure from fluid loss, or indirect, such as dizziness caused by the decrease in blood pressure. It is important for the nurse to teach patients taking diuretics how the drug works and what to expect when taking the drug. Teaching the patient what to expect can increase adherence to the medication regimen. Monitoring daily weight using the same scale at the same time is an important teaching point.

Administration of Potassium-Sparing Diuretics

Dosing of potassium-sparing diuretics can be daily or split into two to four divided doses, depending on patient needs and response. It takes much longer for diuresis to begin with potassium-sparing diuretics than with loop and thiazide diuretics. It is important to assess potassium levels before administration. Because potassium-sparing diuretics cause the body to hold onto potassium, potassium levels can increase with this medication, even when diuresis is present. Spironolactone is not recommended for use in pregnancy.Usual adult dosage of spironolactone is 25 to 200 mg/day.

The nurse is caring for a patient who has heart failure and has developed bilateral crackles in the lungs. Based on onset of action, which diuretic would the nurse anticipate to be prescribed to quickly decrease the fluid? Furosemide Hydrochlorothiazide Spironolactone Amiloride

Furosemide

Furosemide (Lasix)

Furosemide is the most common loop diuretic. It causes a vasodilatory effect, increasing blood flow to the kidneys before diuresis. Loop diuretics begin to work in the body very quickly.

Contraindications of loop diuretics

Hepatic coma, known drug allergy, hypovolemia, and anuria are absolute contraindications. Allergy to sulfonamides was once considered an absolute contraindication. However, evidence indicates that cross-reactions are unlikely. Furosemide carries a black box warning due its diuresis potency. This drug can cause profound water and electrolyte depletion. Careful monitoring is required, and dosage must be based on individual patient response.

Drug Interactions with loop diuretics

If the patient takes digoxin while taking a loop diuretic, this can lead to digoxin toxicity. Monitoring potassium levels is essential as hypokalemia can increase the risk for digoxin toxicity and make the patient more susceptible to dysrhythmias. Other drugs that interact with loop diuretics include aminoglycosides, vancomycin, corticosteroids, lithium, nonsteroidal antiinflammatory drugs (NSAIDs), and antidiabetic drugs.

Administration of loop diuretics

PO Administration Dosing of furosemide can be daily, twice a day, or even every other day, depending on patient needs and response. Diuresis usually starts within an hour of administration. It is important to avoid diuretics at night to minimize nocturia. If loop diuretics are needed twice daily, dosing times are often scheduled at 8 a.m. and 2 p.m. to minimize sleep interruption. If the medication causes stomach upset, it can be taken with food. Parenteral Administration Administer IV doses of furosemide slowly at a rate of 20 mg/min to avoid ototoxicity. Ototoxicity or hearing loss caused by rapid administration or high doses is usually reversible. Monitor the IV site to ensure patency before IV administration. IV administration can cause rapid diuresis, which can lead to incontinence. Because of rapid diuresis, positional hypotension can occur.

Potassium-sparing diuretics

Potassium-sparing diuretics work in the collecting tubules of the kidneys. They act by promoting sodium and water excretion and potassium retention. Spironolactone prevents aldosterone's action, and effects can take 1 to 2 days. The diuretic effect of potassium-sparing diuretics is weak when compared to thiazide and loop diuretics. Potassium-sparing diuretics are often used in conjunction with thiazide or loop diuretics to counteract the potassium-wasting effects.

Side effects of thiazide diuretics

Side effects include hyperuricemia, nausea, vomiting, anorexia, rash, and orthostatic hypotension. Thiazide diuretics do not cause the side effect of ototoxicity (hearing loss). Adverse effects of thiazide diuretics are very similar to the adverse effects of loop diuretics. Adverse effects may include hyponatremia, hypochloremia, dehydration, hypokalemia, and hyperglycemia.

Side effects of loop diuretics

Side effects include ototoxicity (hearing loss), rash, pruritus, nausea, diarrhea, and hyperuricemia. Adverse effects may include hypokalemia, severe dehydration, hyponatremia, hypochloremia, hypotension, hyperglycemia, renal failure, thrombocytopenia, and circulatory collapse.