Overview
This lecture covers the major classes of diuretics, focusing on their sites of action, mechanisms, key indications, potential complications, and clinical strategies for their use in managing volume overload and electrolyte imbalances.
Diuretic Classes & Mechanisms
- Carbonic Anhydrase Inhibitors (e.g., acetazolamide) block carbonic anhydrase in the proximal tubule, decreasing bicarbonate and sodium reabsorption.
- Loop Diuretics (e.g., furosemide) inhibit the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle, causing loss of sodium, chloride, potassium, calcium, and magnesium.
- Thiazide Diuretics (e.g., hydrochlorothiazide) block the Na-Cl cotransporter in the early distal convoluted tubule, increasing sodium loss and enhancing calcium reabsorption.
- Potassium-Sparing Diuretics act in the late distal tubule and collecting duct by blocking ENaC channels (amiloride, triamterene) or antagonizing aldosterone (spironolactone, eplerenone).
Indications and Uses
- Carbonic Anhydrase Inhibitors: adjunct in hypervolemia with metabolic alkalosis, altitude sickness, glaucoma, and idiopathic intracranial hypertension.
- Loop Diuretics: first-line for hypervolemia (edema, heart failure, pulmonary edema), useful for hypercalcemia and hyperkalemia.
- Thiazides: adjunct in hypervolemia with hypernatremia, prevention of calcium kidney stones, osteoporosis, and hypertension.
- Potassium-Sparing Diuretics: adjunct for hypokalemia during diuresis, primary therapy for hyperaldosteronism, cirrhosis, and adjunct in heart failure to reduce mortality.
Major Complications and Side Effects
- Carbonic Anhydrase Inhibitors: metabolic acidosis.
- Loop Diuretics: hypovolemia, hypokalemia, metabolic alkalosis, hypocalcemia, hypomagnesemia, gout, and ototoxicity (especially with high doses).
- Thiazides: hyponatremia, hypokalemia, hypercalcemia, metabolic alkalosis, gout, hypotension.
- Potassium-Sparing Diuretics: hyperkalemia, metabolic acidosis, gynecomastia (with aldosterone antagonists), hyponatremia (rare), lower risk of hypovolemia.
Diuretic Dosing & Clinical Strategy
- Identify volume status (hypovolemic: stop diuretics, possibly give fluids; hypervolemic: start/adjust diuretics).
- Loop diuretics have threshold and ceiling doses; increase frequency, not above ceiling.
- Add thiazide if sodium rises, potassium-sparing if persistent hypokalemia, or carbonic anhydrase inhibitor if metabolic alkalosis develops.
- Monitor daily weights, electrolytes, renal function, and volume status indicators.
Key Terms & Definitions
- Diuresis — increased urine production via enhanced renal excretion of water and solutes.
- Natriuresis — excretion of sodium in the urine.
- Metabolic alkalosis — blood pH increases due to loss of protons or gain of bicarbonate.
- Metabolic acidosis — blood pH decreases due to accumulation of acid or loss of bicarbonate.
- Hypervolemia — excess fluid in the blood.
- Hypovolemia — decreased circulating blood volume.
Action Items / Next Steps
- Review mechanisms, locations, and side effects of each diuretic class.
- Memorize common drug names within each diuretic family.
- Practice clinical scenarios to determine appropriate diuretic choice and escalation.
- Monitor patient labs and signs for complications when prescribing diuretics.