Hypokalaemia in Heart Failure on Furosemide: Oral Potassium Replacement

Patient B-217 is a 66-year-old man with heart failure with reduced ejection fraction. He presents with a 3-day history of increasing weakness and fatigue. He is already established on furosemide 40 mg by mouth once daily, lisinopril 5 mg by mouth once daily, and bisoprolol 2.5 mg by mouth once daily. There are no known drug allergies. On examination he is comfortable, blood pressure 128/78 mmHg, heart rate 92 bpm with a regular rhythm, respiratory rate 16 per minute and oxygen saturations 96% on room air. There is no acute pulmonary oedema, but he has mild bilateral ankle oedema. His weight is 78 kg. Investigation results from this admission: serum sodium 134 mmol/L, serum potassium 2.9 mmol/L, serum creatinine 1.0 mg/dL (eGFR 90 mL/min/1.73 m2), urea 6.5 mmol/L, and a venous blood gas shows a mild metabolic alkalosis with a bicarbonate of 30 mmol/L. An ECG shows normal sinus rhythm with prominent U waves. A serum magnesium level has not been measured. You are asked to prescribe appropriate oral potassium replacement and to comment on the management of his diuretic therapy.