Nausea, yellow-tinged vision and bradycardia in an 80-year-old woman on digoxin

An 80-year-old woman was admitted with a three-day history of progressive nausea, vomiting, and yellow-tinged vision. Her family reported that she had been increasingly lethargic. She had a background of atrial fibrillation, heart failure with preserved ejection fraction, and hypertension. Her regular medications were digoxin 125 micrograms once daily, furosemide 40 mg once daily, and lisinopril 10 mg once daily. She had been taking these for over a year. Ten days before admission, she developed an episode of gastroenteritis with diarrhoea and reduced oral intake. During that period she stopped her furosemide on her own for two days, but then resumed it. Over the subsequent week she noticed worsening nausea and vomiting, and she described the colour of objects as "yellowish". On examination, she was clinically dry, with a pulse of 42 beats per minute and blood pressure of 110/70 mmHg. Her respiratory rate was 18 per minute. There was no organomegaly. Electrocardiography showed atrial fibrillation with a slow ventricular response, and no acute ischaemic changes. Laboratory investigations showed creatinine 220 micromol/L (estimated GFR 22 mL/min/1.73 m2), compared with a baseline creatinine of 120 micromol/L (GFR 45) three months earlier. Serum potassium was 5.1 mmol/L. Her serum digoxin concentration was 3.2 ng/mL (therapeutic range 0.5-0.9 ng/mL). Her haemoglobin was 122 g/L, and liver function tests were normal. Thyroid function tests were unremarkable. She was treated with intravenous fluids. Digoxin was withheld. Over the next 48 hours, her nausea and visual symptoms resolved, and her pulse improved to 68 beats per minute. Her creatinine slowly improved to 180 micromol/L with rehydration. She remained off digoxin and was monitored for six days. She was not rechallenged with digoxin.