So Bored I Started Seeing Yellow: A Review of Digoxin Toxicity

An 87-year-old male was brought in by EMS from a nursing home for altered mental status. As per nursing home’s staff, the patient has been less responsive since yesterday. No fever or change in medication was reported. You are not able to get a hold of the patient’s primary care physician or his nurse.

As the triage nurse is placing the patient on the monitor, you review prior medical records. The patient has a history of congestive heart failure, hypertension, diabetes, rheumatoid arthritis, and hypothyroidism. He has no recent hospitalizations. He is currently on aspirin, lisinopril, carvedilol, digoxin, and levothyroxine. As you review his last office visit, you realize that the patient’s digoxin dose was recently increased.

You start to think about possible digoxin toxicity….

1- What is digoxin?

Digoxin is a cardiac glycoside used in heart failure patients to increase cardiac output through its positive inotropic effect.

2- What is digoxin’s mechanism of action?

Digoxin works by inhibiting Na+/K+ ATPase, whose function works to increase intracellular Na+ and extracellular K+.

3- What is the most common electrolyte abnormality associated with digoxin toxicity?

Hyperkalemia

4- What are the symptoms of digoxin toxicity?

Digoxin side effects can be categorized into non-cardiac vs. cardiac symptoms/signs. Patients who overdose on digoxin initially present with gastrointestinal symptoms in the first 1-2 hours such as nausea, vomiting, and abdominal pain. Patients may also complain of blurry, yellow vision (xanthopsia). Neurological findings such as a headache, confusion, and delirium may be common in elderly.

In severe digoxin toxicity, these symptoms can progress rapidly to those related to cardiac dysrhythmias caused by AV nodal blockade and hyperkalemia such as bradydysrhythmias or ventricular fibrillation.

5- What is the most common ECG finding in a setting of digoxin toxicity?

Premature ventricular contractions (PVCs)

6- Which is the drug of choice for treating digoxin toxicity?

Digoxin-specific antibody

7- What are the indications to administer digoxin-specific antibody?

-Ventricular dysrhythmias

-Symptomatic bradycardia unresponsive to atropine

-Hyperkalemia >5.0 mEq/L in presence of digoxin intoxication

-Co-ingestions of cardiotoxic drugs (beta-blockers, cyclic antidepressants)

-Acute digoxin ingestion of > 10mg in adults or > 4mg in children

-Acute digoxin ingestions with post distribution digoxin >10ng/mL (by 6 hours post ingestion)

-Chronic digoxin ingestion leading to steady-state serum digoxin concentrations of > 4ng/ml

8- What is the correct dose of digoxin-specific antibody

when:

a) neither the digoxin level nor amount ingested is known?

10 vials of Fab fragments (can start with 5 in children)

Repeat if clinical response is inadequate

b) an amount of digoxin is known but concentration is unknown?

Calculate the total body load (TBL)

TBL = Digoxin dose (mg) ingested x 0.8

# of vials = TBL / 0.5 (round up to whole number)

c) digoxin concentration is known?

# vials = [serum digoxin concentration (ng/ml) x patient’s weight in kg] / 100

d) there is a cardiac arrest?

20 vials

9- The administration of which medication may be contraindicated in a setting of digoxin toxicity?

Intravenous calcium is believed to be contraindicated in patients with digoxin toxicity. It was theorized in a 1936 case report that calcium may cause an irreversible non-contractile state (stone heart) by impairing diastolic relaxation in the presence of Na/K channel blockade by digoxin.

Bonus Question: Digoxin is derived from what common flowering plant?

Foxglove