Pharmacology · Year 2 · from Pharmacology
Case 1: Digoxin Toxicity in Renal Impairment
Clinical Scenario
A 78-year-old female with a history of atrial fibrillation and heart failure with reduced ejection fraction presents to the emergency department with nausea, vomiting, and visual disturbances described as "yellow halos around lights."
Patient Demographics
- Age: 78 years
- Sex: Female
- Weight: 55 kg
Chief Complaint
Nausea, vomiting, confusion, and visual changes for 2 days
History of Present Illness
The patient has been on digoxin 0.25 mg daily for rate control of atrial fibrillation for the past 5 years. She was recently started on lisinopril 10 mg for hypertension management. She reports decreased appetite, fatigue, and seeing "yellow-green halos" around lights. Her daughter notes increased confusion over the past 48 hours.
Physical Examination
- Vital Signs: BP 100/65 mmHg, HR 48 bpm (irregular), RR 16, T 36.8C, SpO2 97% on RA
- General: Elderly female appearing fatigued and confused
- Cardiovascular: Irregular rhythm, bradycardic, no murmurs
- Neurological: Oriented to person only, sluggish responses
- HEENT: Pupils reactive, patient reports blurred vision
Workup and Results
| Test | Result | Reference Range |
|---|---|---|
| Digoxin level | 3.8 ng/mL | 0.8-2.0 ng/mL |
| Potassium | 5.8 mEq/L | 3.5-5.0 mEq/L |
| Creatinine | 2.4 mg/dL | 0.6-1.2 mg/dL |
| BUN | 48 mg/dL | 7-20 mg/dL |
| Magnesium | 1.6 mEq/L | 1.5-2.5 mEq/L |
ECG Findings: Atrial fibrillation with slow ventricular response (48 bpm), bidirectional ventricular ectopy, ST segment "scooping" consistent with digoxin effect
Diagnosis
Digoxin toxicity secondary to decreased renal clearance (acute kidney injury) and drug interaction with ACE inhibitor
Pharmacokinetic Principles Illustrated
- Renal elimination: Digoxin is primarily eliminated by the kidneys (60-80%). Decreased GFR leads to drug accumulation and toxicity.
- Drug interactions: ACE inhibitors can reduce renal function and increase digoxin levels.
- Narrow therapeutic index: Digoxin has a therapeutic range of 0.8-2.0 ng/mL with toxicity occurring at levels only slightly above this range.
- Half-life prolongation: In renal impairment, digoxin half-life increases from 36-48 hours to 4-6 days.
Treatment
- Hold digoxin immediately
- Administer Digoxin Immune Fab (Digibind) for life-threatening arrhythmias
- Correct hyperkalemia with calcium gluconate, insulin/glucose, and sodium bicarbonate
- IV fluids for volume resuscitation
- Cardiac monitoring in ICU
- Temporary pacing if symptomatic bradycardia persists
Clinical Image
ECG showing characteristic digoxin effect with "scooped" ST segments. In toxicity, various arrhythmias may be seen including bidirectional ventricular tachycardia.
Image Source: Wikimedia Commons License: Public Domain URL: https://commons.wikimedia.org/wiki/File:ECG_digoxin_effect.png