Digoxin side effects

INTRODUCTION

Digoxin is derived from foxglove (a flowering plant of the plant genus digitalis). According to the National Capital Poison Center, “all parts of the plant are poisonous, possibly even deadly, if swallowed.”

MECHANISM OF ACTION

Fundamentally, digoxin is a poison. It exerts its therapeutic effect by poisoning a cell membrane protein known as the sodium-potassium ATPase (Na+/K+ pump). When this pump is poisoned, sodium accumulates within the cell (the therapeutic target being cardiac muscle cells). Another cell membrane protein called the sodium-calcium exchanger normally exchanges intracellular calcium for extracellular sodium. However, when the concentration of sodium inside the cell is high (as is the case for someone taking digoxin), the sodium-calcium exchanger shuts down. The consequence? Calcium accumulates within the cardiac muscle cell, which causes the heart to contract more forcefully. This can be useful for patients with heart failure.

Digoxin also stimulates the vagus nerve, which has the effect of slowing the conduction of electrical impulses. For this reason, digoxin can also be used to treat atrial fibrillation.

SIDE EFFECTS

The probability that an individual will experience side effects from digoxin is roughly 1 in 5 (20%). Side effects tend to affect one of three systems: #1 cardiac conduction system (e.g., bradycardia, tachycardia, atrioventricular (AV) block, ventricular arrhythmia); #2 central nervous system (e.g., headache, weakness, dizziness, apathy, confusion, depression, anxiety, delirium, hallucinations); #3 gastrointestinal system (e.g., diarrhea, nausea/vomiting, abdominal pain, intestinal ischemia, intestinal hemorrhagic necrosis).

DIGOXIN TOXICITY

Digoxin is a “narrow therapeutic index drug,” meaning that the difference between a dose that will result in therapeutic failure and a dose that will cause life-threatening toxicity is very small. Somewhere in the middle (a very narrow window) is the therapeutic window. That’s what doctors are aiming for, and the thing is… it is slightly different in every patient. So, the doctor will consider the clinical response of the patient in conjunction with the serum concentration of digoxin to optimize the dose and avoid overt toxicity.

“Digoxin toxicity” is a condition characterized by nausea/vomiting, cardiovascular symptoms (e.g., cardiac arrhythmias), yellow-green visual color disturbances/halo effect, dizziness, and fatigue (Cummings et al.). The symptoms can vary from one patient to another. For instance, many elderly patients exhibit vague symptoms such as dizziness and fatigue, making the diagnosis more difficult. If toxicity is suspected, the physician will order a blood test to check the serum digoxin level. Digoxin toxicity is most likely to occur when the serum digoxin concentration exceeds 2.0 ng/mL.

DIGOXIN TOXICITY TREATMENTS

If digoxin toxicity does occur, treatment do exist. For instance, in the case of a large overdose, an antidote can be given (digoxin immune Fab), which is 80-90% effective in reversing digoxin toxicity. Despite the availability of this and other treatments, digoxin toxicity is a very serious condition. Consider the following quote: “When treated promptly, the outcomes are good, but any delay in treatment can lead to death” (Cummings et al.).

PROBABILITY OF DIGOXIN TOXICITY: 1-4%

In any given patient taking digoxin, the risk of digoxin toxicity is somewhere between 1 in 100 (1%) and 1 in 25 (4%). The risk rises with age. For instance, in those age greater than 40, the risk of toxicity is 1%; however, in those age greater than 85, the risk is closer to 4% (David et al.).

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REFERENCES

Digoxin [package insert]. Eatontown, NJ: Hikma Pharmaceuticals USA Inc; 2019.

Cummings ED, Swoboda HD. Digoxin Toxicity. [Updated 2023 Mar 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470568/

David MNV, Shetty M. Digoxin. In: StatPearls. Treasure Island (FL): StatPearls Publishing; January 19, 2023.

One response to “Digoxin side effects”

  1. Lawrence Watkins Avatar

    Way cool! Some extremely valid points! I appreciate you penning this write-up and the rest of the site is also really good.

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