Thiazide Diuretics

Summary

The thiazide diuretics include drugs that end in thiazide, such as chlorothiazide and hydrochlorothiazide. It also includes the thiazide-like diuretics metolazone, chlorthalidone, and indapamide.

These medications work in the distal convoluted tubule of the kidney, where they increase urine output by blocking sodium and chloride reabsorption. Thiazide diuretics are sulfa drugs. They require healthy kidney function for their effect.

Clinically, thiazides are used to treat edema and heart failure. They are also a first-choice treatment for hypertension.

Side effects of thiazides include hypotension, hypercholesterolemia, hyperuricemia, dehydration, hyperglycemia, photosensitivity and orthostatic hypotension. Thiazide diuretics can also cause hyponatremia, so they should be used cautiously in patients taking lithium. They can also cause hypokalemia and should be used with caution in patients taking digoxin. Other side effects include hypercalcemia and hypomagnesemia.

Patients on thiazide diuretics should measure their weight daily to monitor their fluid status, and take the diuretic in the morning to prevent frequent nighttime urination.


Key Points

• Thiazide Diuretics
  • Drug Names
    • -thiazide Ending
      • Hydrochlorothiazide (HCTZ)
      • Chlorothiazide
    • Thiazide-like drugs
      • Indapamide
      • Chlorthalidone
      • Metolazone
  • Mechanism
    • Acts in the distal convoluted tubule
    • Blocks reabsorption of sodium and chloride
      • This increases the amount of sodium and chloride excreted in the urine
      • Fluid follows these electrolytes, thus increasing urine output
    • Needs normal renal function
      • Monitor GFR, creatinine clearance, and BUN
      • Thiazide diuretics will not have desired effects in patients with severe kidney damage
    • Sulfa drug
      • Patients allergic to other sulfa drugs (e.g. sulfonamides, sulfasalazine) may also be sensitive to thiazide diuretics
  • Clinical Use
    • Hypertension
      • First choice drug
      • Diuresis decreases the amount of water in the body, including in the blood vessels, thus decreasing blood pressure
    • Edema
      • Thiazide diuretics help treat peripheral edema, a common side effect of heart failure
      • Can also be used to treat edema from liver failure or kidney disease
    • Heart Failure
      • By removing fluid, thiazide diuretics decrease blood volume and reduce the workload of the heart
    • Kidney Stones (Renal Calculi)
      • Kidney stones are often made of calcium deposits, and thiazide diuretics actually retain calcium in the body
      • Less calcium + more fluid in the urine → less risk of developing kidney stones
  • Side Effects
    • Electrolyte Imbalances
      • Hypokalemia
        • Often called “potassium wasting”
        • Encourage patients to eat a high potassium diet
        • Use digoxin with caution - hypokalemia can cause digoxin toxicity
      • Hyponatremia
        • Use lithium with caution - hyponatremia can cause lithium toxicity
      • Hypercalcemia
        • Unlike loop diuretics, which cause hypocalcemia, thiazide diuretics actually retain calcium in the body
      • Hypomagnesemia
    • Hyperglycemia
      • Use with caution in diabetic patients
      • Monitor blood glucose levels
    • Hyperuricemia
      • Increases uric acid levels, putting patient at an increased risk for developing gout
    • Hypercholesterolemia
      • Increases cholesterol levels
      • Use with caution in patients who have high cholesterol
    • Hypotension
      • If too much fluid is removed from the body, the blood pressure can drop below normal levels
    • Orthostatic hypotension
      • A drop in blood pressure seen when changing positions (e.g. laying or sitting to standing)
      • Educate patients to change positions slowly to avoid dizziness and falls
    • Dehydration
      • Maintain adequate fluid intake to prevent dehydration
    • Photosensitivity
      • Use sunscreen and protective clothing when outdoors
  • Nursing Considerations
    • Take daily weights
      • One of the best way to monitor fluid retention/loss in the body is by weighing the patient daily
      • For best results, weigh around the same time each day with the same amount of clothing
      • Weight gain should be reported, as it is an indication that the patient may not be losing fluid like they’re supposed to
    • Administer early in the day
      • Administering too close to bedtime can cause nocturia, disrupting the patient’s sleep patterns and increasing their risk for falls