Drugs that Affect Fluid and Electrolyte Balance Notes

Objectives

  • Review pathophysiology of the kidneys
  • Discuss medications for fluid imbalances and electrolyte disorders
  • Apply concepts to assessment questions

Kidney Functions

  • Cleansing of extracellular fluid (ECF)
  • Maintenance of ECF volume and composition
  • Maintenance of acid-base balance
  • Excretion of metabolic wastes and foreign substances

Diuretics Overview

  • Types of Diuretics:
    • Loop Diuretics (e.g., Furosemide)
    • Thiazide Diuretics (e.g., Hydrochlorothiazide)
    • Potassium-Sparing Diuretics (e.g., Spironolactone)
    • Osmotic Diuretics (e.g., Mannitol)

Loop Diuretics

  • Furosemide Pharmacokinetics:
    • Onset: 5 mins (IV), 30-60 mins (oral)
    • Elimination: Urine (oral 50%, IV 80%)
  • Adverse Effects:
    • Hyponatremia, Hypochloremia, Dehydration, Hypotension, Hypokalemia, Ototoxicity (rare)

Thiazide Diuretics

  • Hydrochlorothiazide Pharmacokinetics:
    • Onset: Well absorbed, reduced in CHF
    • Elimination: Urine (≥61% unchanged)
  • Adverse Effects:
    • Hyponatremia, Hypochloremia, Dehydration, Hypotension, Hypokalemia, Photosensitivity

Potassium-Sparing Diuretics

  • Spironolactone Pharmacokinetics:
    • Absorption increased by high-fat meals
    • Elimination via urine (as metabolites)
  • Adverse Effects:
    • Hyperkalemia, Gynecomastia, Menstrual irregularities, Impotence, Hirsutism, Deepening voice

Mannitol (Osmotic Diuretic)

  • Pharmacokinetics:
    • Onset: 1-3 hours
    • Elimination: Urine (~80% unchanged)
  • Adverse Effects:
    • Edema

Key Assessment Questions

  1. Antidiuretic hormone affects the kidney reabsorption of which substance?
  2. In chronic kidney disease, which diuretic might be administered?
  3. For left-sided heart failure, which assessment indicates a therapeutic effect of a loop diuretic?
  4. Recommended diuretic for initial therapy of essential hypertension?