What are the different types of diuretics and when to prescribe each one?

Types of Diuretics and When to Prescribe Each

Loop Diuretics: First-Line for Heart Failure and Severe Fluid Overload

Loop diuretics (furosemide, bumetanide, torsemide) are the primary diuretics for heart failure and any condition requiring significant fluid removal, and should be prescribed to all patients with evidence of fluid retention. 1

When to Prescribe Loop Diuretics:

• Heart failure with any degree of fluid retention - Loop diuretics improve symptoms and reduce mortality/morbidity compared to placebo 1
• Acute decompensated heart failure - Start with IV furosemide 20-40 mg for new-onset cases, or at least equivalent to home oral dose for chronic patients 1, 2
• Chronic kidney disease (GFR <30 mL/min) - Loop diuretics maintain efficacy even in severe renal impairment, unlike thiazides 1, 3
• Severe edema requiring rapid diuresis - Loop diuretics produce more intense (though shorter) diuresis than thiazides 1

Dosing Algorithm:

• Initial dose: Furosemide 20-40 mg, bumetanide 0.5-1.0 mg, or torsemide 10-20 mg 1, 3
• Titration: Increase by 20-40 mg furosemide equivalents every 6-8 hours until adequate diuresis achieved 1, 4
• Maximum doses: Furosemide up to 600 mg/day, bumetanide 10 mg/day, torsemide 200 mg/day 1, 3
• Maintenance: Use lowest dose that maintains euvolemia; patients can self-adjust based on daily weights 1

Drug Selection Within Class:

• Furosemide is most commonly used but has variable oral bioavailability 3
• Torsemide is preferred when once-daily dosing desired or in heart failure due to superior bioavailability and longer duration (12-16 hours vs 6-8 hours) 1, 3
• Bumetanide has shortest duration (4-6 hours) but most consistent absorption 3

Thiazide Diuretics: First-Line for Hypertension, Adjunct for Resistant Edema

Thiazide diuretics (hydrochlorothiazide, chlorthalidone, metolazone) are the preferred initial diuretic for uncomplicated hypertension but become ineffective as monotherapy when GFR falls below 30 mL/min. 1, 5

When to Prescribe Thiazides:

• Primary hypertension without heart failure - Thiazides reduce cardiovascular events and are acceptable first-line agents 1, 5
• Mild fluid retention with preserved renal function (GFR >30 mL/min) 1
• Combination therapy for diuretic resistance - Add to loop diuretics when progressive decrease in efficacy observed (the "braking phenomenon") 1, 6

Critical Dosing for Resistant Edema:

• Metolazone 2.5-10 mg once daily PLUS loop diuretic - This combination provides synergistic sequential nephron blockade for severe resistant edema 1
• Monitor closely: Check electrolytes and creatinine every 5-7 days when using combination therapy due to high risk of severe electrolyte depletion 1, 7

Important Contraindication:

• Do NOT use thiazides alone when GFR <30 mL/min - They are ineffective as monotherapy in moderate-severe renal impairment 1, 3
• Exception: Thiazides can be used synergistically WITH loop diuretics even in severe renal dysfunction 1

Mineralocorticoid Receptor Antagonists (MRAs): Disease-Modifying in Heart Failure

Spironolactone and eplerenone are NOT primarily diuretics but disease-modifying agents that reduce mortality in heart failure with reduced ejection fraction (HFrEF). 1

When to Prescribe MRAs:

• All patients with HFrEF (LVEF <40%) and NYHA Class II-IV symptoms - Start spironolactone 25 mg or eplerenone 25 mg daily, target 50 mg daily 1
• Post-myocardial infarction with heart failure 1
• Persistent hypokalemia despite ACE inhibitor and loop diuretic - Use amiloride or triamterene instead of spironolactone 1

Critical Safety Monitoring:

• Check potassium and creatinine after 5-7 days, then weekly until stable 1
• Contraindicated if baseline potassium >5.0 mEq/L or creatinine >2.5 mg/dL 1
• Avoid during ACE inhibitor initiation - Wait until ACE inhibitor dose stable 1

Algorithmic Approach to Diuretic Selection

Step 1: Identify Primary Indication

• Hypertension alone → Start thiazide (hydrochlorothiazide 25 mg or chlorthalidone 12.5 mg) 1, 5
• Heart failure with fluid retention → Start loop diuretic (furosemide 20-40 mg) 1
• Acute pulmonary edema → IV furosemide 40-80 mg bolus 1, 2

Step 2: Assess Renal Function

• GFR >30 mL/min → Thiazides effective as monotherapy 1
• GFR <30 mL/min → Loop diuretics required; thiazides ineffective alone 1, 3

Step 3: Evaluate Response After 6-8 Hours

• Adequate diuresis (>100 mL/hour urine output) → Continue current dose 2
• Inadequate response → Double loop diuretic dose OR add thiazide for sequential blockade 1, 6

Step 4: Address Diuretic Resistance

• First: Increase loop diuretic dose to maximum (furosemide 240-600 mg/day) 1
• Second: Add metolazone 2.5-10 mg daily for synergistic effect 1
• Third: Consider IV continuous infusion if boluses failing 2
• Fourth: Consider acetazolamide if hyponatremia present (thiazides worsen this) 6
• Last resort: Ultrafiltration for refractory resistance 6

Common Pitfalls and How to Avoid Them

Pitfall 1: Using Thiazides in Advanced CKD

Error: Prescribing hydrochlorothiazide monotherapy when GFR <30 mL/min 1
Solution: Switch to loop diuretic; only use thiazides in combination with loop diuretics in this setting 1, 3

Pitfall 2: Inadequate Electrolyte Monitoring

Error: Not checking potassium/magnesium when combining diuretics 1, 7
Solution: Check electrolytes within 5-7 days of any dose change or combination therapy 1

Pitfall 3: Starting MRAs Too Early

Error: Adding spironolactone during ACE inhibitor titration 1
Solution: Wait until ACE inhibitor dose stable, then add MRA with close potassium monitoring 1

Pitfall 4: Giving Diuretics in Hypotension

Error: Administering diuretics when systolic BP <90 mmHg 1, 8
**Solution**: Avoid diuretics entirely; consider vasodilators if SBP >110 mmHg or inotropes/vasopressors if cardiogenic shock 1, 8

Pitfall 5: Underdosing Loop Diuretics

Error: Using furosemide 20 mg twice daily for severe heart failure 1
Solution: Titrate aggressively to 240-600 mg/day if needed to achieve euvolemia 1, 4

Special Clinical Scenarios

Acute Heart Failure with Hypertension (SBP >140 mmHg)

• Start with IV vasodilators (nitroglycerin) PLUS loop diuretics 1
• IV furosemide 40-80 mg bolus, can repeat or switch to continuous infusion 1, 2

Acute Heart Failure with Normotension (SBP 90-140 mmHg)

• Loop diuretics are primary therapy 1
• Start furosemide 20-40 mg IV, titrate based on urine output 1, 2

Chronic Heart Failure Maintenance

• Loop diuretic at lowest effective dose PLUS MRA (spironolactone 25-50 mg) 1
• Patients should monitor daily weights and adjust loop diuretic dose within prescribed range 1

Resistant Edema Despite High-Dose Loop Diuretic

• Add metolazone 2.5 mg daily - This is the most powerful combination 1
• Alternative: Add hydrochlorothiazide 25-50 mg twice daily 1
• Monitor electrolytes every 5-7 days due to profound diuresis risk 1, 7