A 58-year-old man with chronic kidney disease stage 3b (eGFR 35 mL/min/1.73m²) and hypertension presents with ankle edema and a blood pressure of 152/94 mmHg. Serum potassium is 5.8 mEq/L (normal 3.5–5.0), and urinalysis shows 2+ proteinuria. He is currently on lisinopril 10 mg daily. His physician decides to add a diuretic to improve volume status and blood pressure control. Which diuretic is most appropriate in this clinical scenario?

Explanation

## Clinical Context This patient has CKD stage 3b with hyperkalemia (K⁺ = 5.8 mEq/L) and is already on an ACE inhibitor (lisinopril), which reduces aldosterone and increases serum potassium. Adding a potassium-sparing agent would worsen hyperkalemia. ## Why Furosemide Is Correct **Key Point:** Loop diuretics (furosemide) are the diuretics of choice in CKD stage 3–4 because they: - Remain effective even when GFR < 30 mL/min (unlike thiazides) - Promote urinary potassium excretion, helping to lower serum K⁺ - Reduce volume overload and hypertension - Do not accumulate in renal failure **Clinical Pearl:** In a patient already on an ACE inhibitor with hyperkalemia, adding a loop diuretic addresses both the volume problem AND the potassium problem by increasing urinary K⁺ losses. ## Why Other Diuretics Fail in This Setting | Diuretic | Problem in This Patient | |----------|-------------------------| | **Spironolactone** | Potassium-sparing; would worsen hyperkalemia (K⁺ already 5.8). Contraindicated with ACE-I + CKD. | | **Hydrochlorothiazide** | Ineffective in CKD stage 3b (eGFR < 40); poor natriuretic effect. Also causes hypokalemia but not the issue here. | | **Amiloride** | Potassium-sparing; same problem as spironolactone. Dangerous in hyperkalemia + ACE-I. | **High-Yield:** Loop diuretics are first-line for edema + CKD stage 3–4. Potassium-sparing diuretics are contraindicated when serum K⁺ is elevated or when combined with ACE-I/ARB in renal impairment. **Mnemonic — Diuretic Choice by GFR:** - **GFR > 30:** Thiazides or loop diuretics - **GFR < 30:** Loop diuretics only (thiazides lose efficacy) - **Hyperkalemia present:** Avoid potassium-sparing agents; use loop diuretics