A 58-year-old man with chronic kidney disease (eGFR 35 mL/min/1.73m²) and hypertension presents with ankle edema and dyspnea on exertion. His current medications include lisinopril and amlodipine. On examination, BP is 158/94 mmHg, JVP elevated at 8 cm, and bilateral ankle edema present. Serum electrolytes: Na⁺ 138 mEq/L, K⁺ 5.8 mEq/L, Cr 2.1 mg/dL. Echocardiography shows ejection fraction of 45%. Which diuretic is most appropriate for this patient?

Explanation

## Clinical Scenario Analysis This patient has: - Reduced renal function (eGFR 35 mL/min/1.73m²) - Heart failure with reduced ejection fraction (HFrEF, EF 45%) - Fluid overload (edema, elevated JVP, dyspnea) - Hyperkalemia (K⁺ 5.8 mEq/L) - Already on ACE inhibitor (lisinopril) ## Why Furosemide is Correct **Key Point:** Loop diuretics (furosemide) are the first-line agents for symptomatic fluid overload in HFrEF, especially with reduced renal function. **High-Yield:** Furosemide remains effective even when GFR is <30 mL/min because it is secreted into the proximal tubule via organic anion transporters—it does NOT depend on glomerular filtration alone. **Clinical Pearl:** In this patient: - Loop diuretics relieve congestion (ankle edema, dyspnea, elevated JVP) - Thiazides are ineffective when eGFR <30 mL/min - Potassium-sparing agents (spironolactone) are contraindicated due to existing hyperkalemia and reduced renal clearance - Mannitol is reserved for acute cerebral edema or acute renal failure with oliguria—not for chronic HF ## Mechanism in Reduced Renal Function Furosemide blocks the Na⁺-K⁺-2Cl⁻ cotransporter in the thick ascending limb. Even with reduced GFR, active secretion into the tubular lumen ensures drug delivery and efficacy. Dosing may need escalation (e.g., 40–80 mg) to achieve adequate natriuresis. ## Diuretic Efficacy by GFR | Diuretic Class | Effective GFR | Mechanism | Notes | |---|---|---|---| | Loop (furosemide) | >15 mL/min | Tubular secretion | Most reliable in renal impairment | | Thiazide (HCTZ) | >30 mL/min | Glomerular filtration | Ineffective in advanced CKD | | K⁺-sparing (spironolactone) | >30 mL/min | Aldosterone antagonism | Risk of hyperkalemia in CKD | | Osmotic (mannitol) | Variable | Osmotic gradient | Acute settings only; can worsen fluid overload | [cite:KD Tripathi 8e Ch 15]