Captopril and Potassium: Interaction Details

a) Captopril combined with potassium supplements may induce hyperkalemia. Five congestive heart failure patients were administered captopril concurrently with existing potassium supplements. An increase in serum potassium was observed in all patients. Until potassium or captopril were discontinued or the doses reduced, the serum potassium levels remained elevated ¹.

b) An 81-year old woman with a history of congestive heart failure and acute myocardial infarction presented to the hospital with chest discomfort. The patient had been taking diltiazem, furosemide, digoxin, isosorbide mononitrate, and aspirin regularly in addition to captopril 25 mg three times daily. The patient was also taking potassium 1200 mg twice daily due to persistent hypokalemia during an earlier hospitalization. Upon examination and measurement of serum electrolytes, the patient had a slow atrial fibrillation, heart rate of 36 beats per minute, and a serum potassium level of 8.2 mmol/L. After treatment with calcium gluconate, dextrose, insulin, furosemide, and sodium polystyrene sulfonate, the patient's serum potassium level decreased to 5.4 mmol/L and normal sinus rhythm returned. The authors noted that life-threatening hyperkalemia may occur late during the course of treatment with ACE inhibitors, and suggested monitoring of renal function and potassium ².

c) A 59-year old man was admitted to the hospital for treatment of an acute exacerbation of congestive heart failure and hypertension ³. The patient's serum potassium level on admission was 4.3 mEq/L. Captopril 12.5 mg every eight hours was then added to the patient's regimen of furosemide and oral nitrates. The patient's serum potassium level began to increase slowly over the next few days to a level of 5.0 mEq/L. A review of the patient's chart showed that he had been on a salt-restricted diet. The patient had been using several hospital-provided salt substitute packages during every meal, which contained approximately 13 mEq of potassium per gram. When the salt substitute was discontinued, serum potassium levels fell to 4.8 mEq/L.

d) A 64-year old woman presented to the emergency room with a 36-hour history of intermittent vomiting ⁴. The patient was being treated with lisinopril 10 mg daily, and theophylline 600 mg daily. The patient had lost 33.8 kg over the previous six months on a daily diet consisting of a protein supplement containing 48 mmol potassium and an evening salad containing a salt substitute with 72 mmol potassium. The patient complained of severe weakness, had a serum potassium level of 9.7 mmol/L, and showed electrocardiographic changes consistent with hyperkalemia, including a widening of the QRS complex. After the patient was treated with calcium gluconate, insulin, dextrose, and sodium bicarbonate intravenously, serum potassium levels decreased to normal over the next 12 hours. The authors suggested that the patient experienced life-threatening hyperkalemia due to lisinopril inhibition of aldosterone secretion in addition to a diet containing more than 120 mmol potassium per day.

e) Two patients who experienced hyperkalemia due to the addition of salt substitutes containing potassium have been described. The first patient, a 67-year-old male taking atenolol 100 mg daily, furosemide 40 mg daily, aspirin 75 mg daily, and lisinopril 20 mg daily, presented with a three-day history of dizziness and vomiting. His serum potassium was 7.6 mmol/L, and treatment with insulin and dextrose was initiated. An electrocardiogram showed a marked sinus bradycardia, and the patient suffered a brief cardiac arrest. It was discovered that the patient had been adding 70 mmol of potassium daily to his diet in the form of a salt substitute one week prior to admission, which was believed to be the cause of his hyperkalemia. The second patient, a 64-year-old male, was started on enalapril 2.5 mg twice daily for hypertension and had a serum potassium level of 5 mmol/L. Four months later, his potassium had increased to 7 mmol/L. The hyperkalemia was corrected with insulin and dextrose, while the enalapril was discontinued. The patient mentioned that he had started using a salt substitute, and further investigation revealed that he was adding 133 mmol of potassium daily into his diet from the salt substitute. Enalapril was restarted, the salt substitute was discontinued, and two months later his potassium was 5.7 mmol/L ⁵.