Did You Know? Loop Diuretics

Jan 24, 2022 | Clinical Insight

Main Indications:

  • Fluid retention in heart failure and kidney disease
  • Hypertension

Special notes:

  • The loop diuretics are more potent diuretics than thiazides, but less effective antihypertensives in most patients.1
  • Loop diuretics are recommended over thiazides in patients with renal impairment (GFR < 30 ml/min) due to decreased efficacy of the thiazides in this patient population. However, a thiazide can be added to a loop to enhance diuresis.2

How Do They Work?

  • Loop diuretics work in the loop of Henle in the kidney (Fig. 1). They reduce sodium reabsorption, which causes the elimination of water and sodium from the body.
Fig. 1

Differences:

Bioavailability: A measure of the rate and fraction of the initial dose of a drug that successfully reaches either; the site of action or the bodily fluid domain from which the drug’s intended targets have unimpeded access3:

  • Furosemide is 10-100% (varies from patient to patient)
  • Bumetanide and Torsemide are both about 80-100 %

Half-life:

  • Furosemide and Bumetanide 4-6 hours
  • Torsemide has a much longer half-life, allowing for once daily dosing: ~12-16 hours

Equivalent Dosing4:

  • Furosemide 40 mg=Torsemide 20 mg=Bumex 1 mg=Ethacrynic acid 50 mg
  • Ethacrynic acid is a loop diuretic that can be used in those with a Sulfa allergy as it does not contain a sulfa group. This particular loop is more ototoxic than the other loop diuretics.

Monitoring:

  • Electrolytes
    • Diuretics can cause hypokalemia and potassium supplementation is often required. General rule: 20 mEq of potassium per 40 mg of Furosemide.
    • Magnesium loss can also be seen and therefore should be checked at least annually
  • Weights, blood pressure, and renal function should also be monitored

References:

  1. Cheng JW. Essential hypertension. In: Zeind CS, Carvalho MG. Koda-Kimble & Young’s Applied Therapeutics: the Clinical Use of Drugs. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2018: 132-61.
  2. Singh H, Marrs JC. Heart failure. In: Zeind CS, Carvalho MG. Koda-Kimble & Young’s Applied Therapeutics: the Clinical Use of Drugs. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2018: 261-305.
  3. Currie GM. Pharmacology, Part 2: Introduction to Pharmacokinetics. J Nucl Med Technol. 2018 Sep;46(3):221-230.
  4. Pham D, et al. Card Fail Rev 2017; 3:108-12.

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Brandi VanValkenburg

Brandi provides personalized care as a pharmacy consultant with HealthDirect's northeastern region.  She has been serving our clients for over 10 years. 

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