Diuretics: Classes, Electrolyte Effects, and Nursing Safety

This note reviews the three major classes of diuretics, where they act in the nephron, their electrolyte effects, common side effects, and the nursing priorities that keep patients safe. Diuretics are high-yield on nursing exams because small mistakes — like giving spironolactone with a potassium supplement — can cause life-threatening dysrhythmias.

Diuretic Classes

• Loop diuretics — example: furosemide. "Loops lose K⁺."
• Thiazide diuretics — example: hydrochlorothiazide. Moderate-strength diuretic.
• Potassium-sparing diuretics — example: spironolactone. Potassium saver.

Site of Action

• Loop diuretics: Loop of Henle
• Thiazide diuretics: Distal tubule
• Potassium-sparing diuretics: Collecting duct

Electrolyte Effects

• Loop: ↓ potassium, ↓ sodium, ↓ calcium
• Thiazide: ↓ potassium, ↓ sodium, ↑ calcium
• Potassium-sparing: ↑ potassium, ↓ sodium, no change in calcium

Common Side Effects

• Loop: hypokalemia, dehydration, ototoxicity
• Thiazide: hypokalemia, hyperglycemia, hypercalcemia
• Potassium-sparing: hyperkalemia, gynecomastia

Labs to Monitor

• Potassium — risk of dysrhythmias
• Sodium — dehydration risk
• BUN / Creatinine — renal function
• Glucose — thiazides can increase glucose

Nursing Safety Rules

• Check potassium before administration.
• Give diuretics in the morning to avoid nighttime voiding.
• Monitor daily weights to track fluid status.
• Assess blood pressure before and after dosing.
• Encourage potassium-rich foods — but not with potassium-sparing diuretics.

Drug-Specific Exam Pearls

• Loop diuretics are the strongest and are used for pulmonary edema.
• Thiazides are used for long-term hypertension control.
• Potassium-sparing diuretics are often combined with loop or thiazide agents to balance potassium loss.

Common Exam Traps

• Confusing which diuretics lose vs. save potassium.
• Giving spironolactone with potassium supplements (→ hyperkalemia).
• Ignoring abnormal potassium labs before administration.
• Administering diuretics at bedtime.
• Forgetting to monitor daily weights.

Key takeaways

• Loop diuretics are the strongest and lower potassium — watch for hypokalemia and ototoxicity.
• Thiazides lower potassium but raise calcium and glucose.
• Potassium-sparing diuretics raise potassium — never combine with K⁺ supplements.
• Always check potassium before giving any diuretic; electrolyte imbalances cause dysrhythmias.
• Give diuretics in the morning and monitor daily weights, BP, and renal labs.