Loop Diuretics

Furosemide and bumetanide act on the loop of Henle, producing potent diuresis used in heart failure and pulmonary edema. They cause significant potassium, sodium, magnesium, and calcium wasting, so monitor for hypokalemia (muscle weakness, dysrhythmias) and hypomagnesemia. Rapid IV administration can cause ototoxicity, especially with concurrent aminoglycosides, so IV push should be given slowly over 1-2 minutes. Because loop diuretics increase digoxin toxicity risk through hypokalemia, always check potassium before administering digoxin in a patient on both drugs.

Thiazide and Potassium-Sparing Diuretics

Thiazides (hydrochlorothiazide) are first-line for hypertension and also cause hypokalemia and hyponatremia but uniquely cause hypercalcemia by increasing calcium reabsorption, contrasting with loop diuretics. They are less effective with reduced renal function (GFR under 30). Potassium-sparing diuretics (spironolactone) block aldosterone, conserving potassium while eliminating sodium and water, making them useful in heart failure and cirrhosis but risky when combined with ACE inhibitors, ARBs, or potassium supplements due to hyperkalemia. Spironolactone also causes gynecomastia in men from its antiandrogen effect.

Monitoring and Patient Teaching

Daily weights at the same time, same scale, and same clothing are the most sensitive indicator of fluid status — a 2 lb (1 kg) overnight gain equals about 1 liter of retained fluid. Teach patients to take diuretics in the morning to avoid nocturia disrupting sleep, rise slowly to prevent orthostatic falls, and report muscle cramps or weakness suggesting electrolyte imbalance. Encourage potassium-rich foods (bananas, oranges) with potassium-wasting diuretics, but caution against potassium supplements or salt substitutes when on potassium-sparing agents.