Thiazide Diuretics

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Summary

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Key Points

  • Key Drugs
    • End in “-thiazide”
      • Hydrochlorothiazide
      • Chlorothiazide
      • Methyclothiazide
    • Thiazide-like diuretics
      • Chlorthalidone
      • Indapamide
      • Metolazone
    • Mechanism (Saunders)
      • Remove excess fluid (Diuresis)
        • Act on the early distal convoluted tubule to block the reabsorption of sodium, potassium, and water
          • Water loves sodium, so if more sodium is excreted from the body, more water will also be excreted (diuresis)
        • May act directly on arterioles to cause vasodilation, decreasing blood pressure
        • Weaker diuretic and slower onset than loop diuretics, but thiazides are still fairly potent
        • Will lead to increased urination
          • Contraindicated in patient with renal impairment
            • You can anticipate that renal function will be measured through creatinine and BUN
            • The effectiveness of the thiazide diuretic greatly decreases with a creatinine clearance less than 30 mL/min
          • Watch for signs and symptoms of dehydration
          • Take in the morning to avoid nocturia
          • Closely monitor intake and output in the hospital setting. Report urine output less than 30 mL/hour.
          • Take daily weights
            • Best way to determine fluid retention
    • Clinical Use (Saunders, mictlan)
      • Hypertension
        • Hydrochlorothiazide is often combined with an antihypertensive to control high blood pressure
      • Edema
        • Due to heart failure, liver failure, or kidney failure
    • Side Effects and Adverse Reactions (Saunders, mictlan)
      • Fluid electrolyte imbalances
        • Hypokalemia
          • Can lead to muscle cramps and life-threatening heart arrhythmias
          • Potassium supplementation is often needed, or combination with potassium-sparing diuretic like spironolactone
          • The most serious drug reaction occurs with digoxin, as hypokalemia can cause digitalis toxicity
          • Closely monitor potassium levels and hold the drug if the patient’s potassium level is less than 3.5
        • Hyperglycemia
          • Use cautiously in patients with diabetes mellitus
          • Closely monitor blood glucose levels
        • Hyponatremia
          • Low sodium increases risk of lithium toxicity, so be extremely cautious if patient is taking lithium concurrently (generally lithium and thiazides are not taken together)
        • Hypercalcemia
          • In contrast to loop diuretics, which cause hypocalcemia
        • Hypomagnesemia
        • Hypochloremia
      • Increased lithium levels/toxicity
        • Diuresis causes a compensatory increase in reabsorption of cations at the proximal tubule, which increases lithium levels
      • Hyperuricemia
        • Patients are at an increased risk of gout
      • Photosensitivity
        • Related to sulfa drug structure
      • Sulfa drug (can cause allergy)
      • Orthostatic hypotension
        • Results from volume depletion induced by diuresis