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ACE Inhibitor–Associated Hyperkalemia
5 questions · Cardiovascular, Renal and Medication Safety
Clinical Case
A 66-year-old man with hypertension, type 2 diabetes, and chronic kidney disease presents with
muscle weakness and palpitations. His medications include lisinopril 20 mg daily and
spironolactone 25 mg daily. Two weeks ago, he began using a potassium-based salt substitute.
Laboratory results:
Potassium: 6.2 mmol/L
Creatinine: 176 µmol/L, increased from baseline
eGFR: 34 mL/min/1.73 m²
Sodium: 137 mmol/L
What is the primary mechanism of action of lisinopril?
Answer and Clinical Rationale
Correct answer: C. Inhibition of angiotensin-converting enzyme
Lisinopril inhibits angiotensin-converting enzyme, reducing the conversion of angiotensin I to
angiotensin II. This lowers vasoconstriction and aldosterone secretion.
• A describes aliskiren.
• B describes angiotensin-receptor blockers.
• D describes spironolactone and eplerenone.
Which combination most likely caused this patient’s hyperkalemia?
Answer and Clinical Rationale
Correct answer: A. Lisinopril, spironolactone, and potassium salt substitute
Lisinopril reduces aldosterone production, spironolactone blocks aldosterone receptors, and the
salt substitute adds potassium. Chronic kidney disease further reduces potassium elimination.
Which ECG finding is most characteristic of early hyperkalemia?
Answer and Clinical Rationale
Correct answer: B. Peaked T waves
Tall, narrow, peaked T waves are an early ECG manifestation of hyperkalemia. More severe
hyperkalemia can cause PR prolongation, loss of P waves, QRS widening, and a sine-wave
pattern.
What is the most appropriate action?
Answer and Clinical Rationale
Correct answer: C. Arrange urgent medical assessment
A potassium level of 6.2 mmol/L with symptoms and renal deterioration is potentially
life-threatening and requires urgent medical assessment.
Which monitoring is most important after initiating or increasing an ACE inhibitor?
Answer and Clinical Rationale
Correct answer: B. Potassium and renal function
Serum potassium and creatinine should be monitored because ACE inhibitors may cause
hyperkalemia and reduced renal filtration, particularly in patients with chronic kidney disease,
dehydration, renal artery stenosis, or concurrent potassium-retaining therapy.
Open medication overview, safety review, clinical pearl, or NPLEX trap supplied with this case
Disease and medication overview
ACE inhibitors are commonly used for hypertension, diabetic kidney disease, heart failure, and
post-myocardial-infarction ventricular protection. Common adverse effects include cough,
dizziness, hyperkalemia, and increased creatinine. Angioedema is uncommon but potentially
fatal.
NPLEX exam trap
Do not assume salt substitutes are sodium-free and harmless. Many contain substantial
potassium.