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
- Contraindicated in patient with renal impairment
- Act on the early distal convoluted tubule to block the reabsorption of sodium, potassium, and water
- Remove excess fluid (Diuresis)
- 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
- Hypertension
- 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
- Hypokalemia
- 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
- Fluid electrolyte imbalances
- End in “-thiazide”