Glycosides and Congestive Heart Failure

Original Editor - Lauren Pulliam Southern Top Contributors - Lucinda hampton, Kim Jackson, Lauren Pulliam Southern, Beau Lawrence and Aminat Abolade

Introduction

Digoxin, sold under the brand name Lanoxin among others, is a medication used amongst, other things, congestive heart failure CHF. Digoxin increases the force of myocardial contraction,prolongs refractory period of the AV node, and decreases conduction through the SA and AV nodes.

Digoxin is no longer the first choice for heart failure as it may increase the risk of death

Currently, the recommendation for heart failure is a triple therapy of ACE inhibitor, beta blocker and Aldosterone receptor antagonist diuretics . Digoxin is a third-line therapy.

Glycosides

The two types of glycosides used to treat CHF are

• Digoxin, the primary one used. Digoxin is a positive inotropic agent that activates the sodium-calcium membrane exchange pump which increases the intracellular calcium concentrations. This increase in calcium will lead to stronger contractions of the heart.  Digoxin also reduces sympathetic responses via the vagus nerve, which will reduce overall heart rate. The combination of increased contractility and reduced heart rate creates a more efficient pump for cardiac output.
• Digitoxin -  similar in structure and effects to digoxin however the effects are longer-lasting. Unlike digoxin (which is eliminated from the body via the kidneys), it is eliminated via the liver, so could be used in patients with poor kidney function. Today it is rarely used in Western medical practice. The evidence for its effectiveness is not as strong as digoxin.

Administration and Pharmocokinetics

Digoxin is traditionally taken orally, with doses between 0.125mg- 0.25mg daily, with large storage taking place in skeletal muscles.

It is mostly absorbed through the small intestine and metabolized in the liver through hydrolysis, oxidation, and conjugation. Approximately 70% of digoxin is cleared through the kidneys and has a half-life of 36 hours. Toxicity is a common adverse effect caused by higher concentrations of serum Digoxin. Monitoring blood concentrations is important to prevent toxicity, especially if the patient has renal complications or is elderly. Serum digoxin concentration levels should remain between 0.5 nmol/L to 0.9 nmol/L, depending on the body weight of the patient. Chronic toxicity, more common than acute toxicity, may occur if these concentrations reach above the therapeutic dose for a prolonged period of time.

Side effects caused by Toxicity

• dysrhythmias
• anorexia, nausea, vomiting
• altered mental status,
• drowsiness,
• visual disturbances,
• altered potassium levels.

Physiotherapy Implications

Identifying signs the signs of toxicity are critical for a physical therapists to maintain patient safety. Despite these potential negative effects, patients on digoxin can participate in physical therapy better than without the medication. Due to digoxin’s effect on cardiac output, the heart is able to more effectively pump blood into the system, improving the exercise tolerance of the patient.