Digoxin Toxicity in an Older Adult After a New Antibiotic
A 78-year-old woman with chronic heart failure and atrial fibrillation lives alone and takes digoxin 0.25 mg once daily and furosemide 40 mg twice daily. Ten days ago, her general practitioner started clarithromycin 500 mg twice daily for acute bronchitis. She now presents to the outpatient department with nausea, anorexia, and halos around lights. Her pulse is 48/min and irregular; blood pressure is 104/62 mmHg. Her serum potassium is 3.1 mmol/L, creatinine is 1.6 mg/dL, and serum digoxin is 2.6 ng/mL. She says she has not missed any digoxin doses and sometimes takes an extra dose when she feels her heart racing.
1. Explain the likely cause of her symptoms and identify the factors that increased her risk of digoxin toxicity.
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Her symptoms-nausea, anorexia, and halos around lights-plus bradycardia and a digoxin level of 2.6 ng/mL indicate digoxin toxicity. Clarithromycin is the likely precipitant: it inhibits P-glycoprotein and increases digoxin absorption and levels. Furosemide has caused hypokalaemia (3.1 mmol/L), which increases binding of digoxin to sodium-potassium ATPase and potentiates toxicity. Age 78 and creatinine 1.6 mg/dL reduce renal clearance. Her occasional extra doses also increase risk. The usual therapeutic range is 0.5–2.0 ng/mL, so 2.6 is above range.
2. What immediate nursing actions and monitoring would you take before the next dose of digoxin is due?
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Hold the next digoxin dose and notify the prescriber immediately. Obtain a 12-lead ECG and continuous cardiac monitoring for bradycardia, heart block, or ventricular arrhythmias. Recheck potassium, magnesium, renal function, and digoxin level as ordered; treat hypokalaemia cautiously because rapid correction can worsen toxicity in some settings. Do not give calcium, which can be harmful in digoxin toxicity. Assess pulse and blood pressure every 15–30 minutes, monitor urine output, and keep the patient on bed rest with fall precautions. Prepare digoxin immune Fab if severe arrhythmia or hyperkalaemia develops. Review all medicines for interacting drugs, including over-the-counter products.
3. What would you teach her and her family before discharge?
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Teach her to take digoxin exactly as prescribed and never to take an extra dose, even if she feels palpitations. Explain that clarithromycin and some other antibiotics can raise digoxin levels, so she should tell every prescriber and pharmacist that she takes digoxin. Teach her to check her pulse before each dose and to hold it and call the clinic if it is below 60/min or irregular. Report nausea, vomiting, anorexia, visual changes, or confusion. Continue potassium-rich foods unless restricted, keep follow-up appointments for blood tests, and use a pill organiser. Ask a family member to check on her.