Which medication should be discontinued in an elderly patient with hypertension, diabetes type 2, and DVT, on metformin, atorvastatin, lisinopril, and furosemide, with impaired renal function, hyperkalemia, and prolonged PT and APTT, who is being treated with heparin?

Lisinopril Should Be Stopped Immediately

In this elderly patient with hyperkalemia (K+ 6.0 mEq/L) and declining renal function, lisinopril must be discontinued immediately as it is the primary cause of the life-threatening hyperkalemia. 1, 2, 3

Why Lisinopril Must Be Stopped

The ACE inhibitor is directly causing the hyperkalemia through blockade of angiotensin II-mediated aldosterone release, which reduces renal potassium excretion. 1 This patient has reached a potassium level of 6.0 mEq/L, which represents moderate-to-severe hyperkalemia requiring immediate intervention. 1, 2, 3

High-Risk Profile for ACE Inhibitor-Induced Hyperkalemia

This patient has the perfect storm of risk factors:

• Elderly diabetic patients on ACE inhibitors have significantly increased hyperkalemia risk, particularly with declining renal function (creatinine 120 μmol/L, up from baseline 115 μmol/L). 1, 2
• The combination of ACE inhibitor with diabetes and renal insufficiency creates a particularly dangerous scenario for hyperkalemia. 1
• The American Geriatrics Society specifically warns that ACE inhibitors in elderly diabetic patients significantly increase hyperkalemia risk when combined with declining renal function. 2

Guideline-Based Thresholds

• The European Society of Cardiology recommends discontinuing RAAS inhibitors immediately when potassium exceeds 6.5 mEq/L, and this patient at 6.0 mEq/L is approaching this critical threshold. 1, 3
• The American College of Cardiology identifies discontinuing ACE inhibitors as the primary intervention in moderate hyperkalemia with declining renal function. 1, 2, 3

Why Other Medications Should NOT Be Stopped

Heparin (Option A) - Continue

• Heparin is essential for treating the acute DVT and preventing life-threatening pulmonary embolism. 2
• While heparin can cause hyperkalemia through aldosterone suppression, this typically occurs only with prolonged use (>7 days) and is far less pronounced than ACE inhibitor-induced hyperkalemia. 2, 3
• The prolonged PT/APTT is expected with therapeutic heparin anticoagulation for DVT treatment. 2

Furosemide (Option B) - Continue

• Loop diuretics like furosemide actually reduce hyperkalemia risk by promoting urinary potassium excretion and should be continued. 1, 2, 3
• The European Society of Cardiology specifically recommends continuing loop diuretics to promote potassium excretion and help lower serum potassium. 1, 3
• Discontinuing furosemide would worsen the hyperkalemia and is counterproductive. 1

Metformin (Option D) - Continue

• Metformin does not cause hyperkalemia and has no direct effect on potassium homeostasis. 1, 2, 3
• Metformin is safe to continue with eGFR ≥30 mL/min/1.73 m². 1
• The patient's creatinine of 120 μmol/L (approximately 1.4 mg/dL) corresponds to an eGFR well above 30 mL/min/1.73 m² in an elderly patient, making metformin continuation safe. 4
• The American Diabetes Association confirms metformin may be used safely in patients with eGFR ≥30 mL/min/1.73 m². 4

Immediate Management Steps After Stopping Lisinopril

1. Obtain ECG immediately to assess for hyperkalemia-related cardiac changes (peaked T waves, widened QRS complex, which can progress to life-threatening arrhythmias). 1, 3

2. Recheck potassium and creatinine within 24-48 hours after stopping lisinopril to confirm improvement. 1, 3

3. If potassium remains elevated above 5.5 mEq/L after stopping lisinopril, initiate sodium zirconium cyclosilicate or patiromer (newer potassium binders). 1, 3

4. Avoid sodium polystyrene sulfonate (Kayexalate) in this elderly patient due to serious gastrointestinal adverse events including colonic necrosis. 1, 3

Long-Term Blood Pressure Management

• Once potassium normalizes to 4.0-5.0 mEq/L, consider alternative antihypertensive agents that do not affect potassium homeostasis, such as calcium channel blockers (amlodipine). 1, 3
• If cardio-renal protection from RAAS inhibition is deemed essential after hyperkalemia resolution, newer potassium binders can enable reintroduction of lisinopril at lower doses with close monitoring. 1, 3

Critical Pitfalls to Avoid

• Do not continue ACE inhibitors hoping the hyperkalemia will resolve spontaneously - this can lead to life-threatening cardiac arrhythmias. 1
• Do not discontinue furosemide - this will worsen hyperkalemia and fluid overload. 1
• Do not stop heparin - the DVT requires anticoagulation to prevent pulmonary embolism, which carries significant mortality risk. 2
• Do not use older potassium binders like Kayexalate in elderly patients - they carry significant gastrointestinal toxicity risk. 1, 3

Answer: C - Lisinopril