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Digoxin

Digoxin is a cardiac glycoside extracted from the foxglove plant, digitalis. It is widely used in the treatment of various heart conditions, namely atrial fibrillation, atrial flutter and congestive heart failure that cannot be controlled by other medication. more...

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The main effects of digoxin are on the heart, its extracardiac effects are responsible for most of the side effects, i.e. nausea, vomiting, diarrhea and confusion.

Its main cardiac effects are:

A decrease of conduction of electrical impulses through the AV node, making it a commonly used drug in controlling the heart rate during atrial fibrillation or atrial flutter.
An increase of force of contraction via inhibition of the Na⁺/K⁺ ATPase pump (see below).

Mechanism of action

Digoxin binds to a site on the extracellular aspect of the α-subunit of the Na⁺/K⁺ ATPase pump in the membranes of heart cells (myocytes). This causes an increase in the level of sodium ions in the myocytes, which then leads to a rise in the level of calcium ions. The proposed mechanism is the following: inhibition of the Na⁺/K⁺ pump leads to increased Na⁺ levels, which in turn slows down the extrusion of Ca²⁺ via the Na⁺/Ca²⁺ exchange pump. Increased amounts of Ca²⁺ are then stored in the sarcoplasmic reticulum and released by each action potential, which is unchanged by digoxin. This is a different mechanism from that of catecholamines.

Digoxin also increases vagal activity via its central action on the central nervous system, thus decreasing the conduction of electrical impulses through the AV node. This is important for its clinical use in different arrhythmias (see below).

Clinical use

Today, the most common indications for digoxin are probably atrial fibrillation and atrial flutter with rapid ventricular response. High ventricular rate leads to insufficient diastolic filling time. By slowing down the conduction in the AV node and increasing its refractory period, digoxin can reduce the ventricular rate. The arrhythmia itself is not affected, but the pumping function of the heart improves owing to improved filling.

The use of digoxin in congestive heart failure during sinus rhythm is controversial. In theory the increased force of contraction should lead to improved pumping function of the heart, but its effect on prognosis is disputable and digoxin is no longer the first choice for congestive heart failure. However, it can still be useful in patients who remain symptomatic despite proper diuretic and ACE inhibitor treatment.

Digoxin is usually given by mouth, but can also be given by IV injection in urgent situations (the IV injection should be slow, heart rhythm should be monitored). The half life is about 36 hours, digoxin is given once daily, usually in 125μg or 250μg dosing. In patients with decreased kidney function the half life is considerably longer, calling for a reduction in dosing or a switch to a different glycoside (digitoxin).

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Digoxin increases mortality among women with congestive heart failure - Patient Oriented Evidence that Matters
From Journal of Family Practice, 2/1/03 by Sharon See

Rathore SS, Wang Y, Krumholz HM. Sex-based differences in the effect of digoxin for the treatment of heart failure. N Engl J Med 2002; 347:1403-11.

* PRACTICE RECOMMENDATIONS

Digoxin increases mortality in women with congestive heart failure, compared with men; however, the clinical significance of this is unknown since gender is a nonmodifiable risk factor. More importantly, there is a suggestion of harm when looking at women treated with digoxin versus placebo. Since there are other therapies with definite benefit in congestive heart failure (angiotensin-converting enzyme inhibitors, beta-blockers, spironolactone), it is prudent to reconsider the use of digoxin in women with ejection fractions less than 45%.

* BACKGROUND

Is there a difference in the effect of digoxin for heart failure between women and men? This study is a subgroup analysis of the Digitalis Investigaton Group Trial (DIG), which, in 1997, showed that digoxin did not affect mortality in the treatment of heart failure. This subgroup analysis reexamined the data and looked for sex-based differences, which is important because women account for the majority of deaths from congestive heart failure.

* POPULATION STUDIED

The researchers from the original DIG trial enrolled 6800 patients who had stable heart failure with an ejection fraction of 45% or less and who were in normal sinus rhythm. Overall, the women in the study were older than the men, had a shorter duration of heart failure, had a higher median ejection fraction, and had greater disease severity as classified by the New York Heart Association system. The reported results, however, adjust for these differences.

* STUDY DESIGN AND VALIDITY

This is a post hoc analysis of the DIG trial, a randomized, double-blinded, placebo-controlled study of 5281 men and 1519 women randomized to receive either digoxin or placebo. This reanalysis of the DIG data looked at the outcomes separately for men and women.

This analysis (based on sex) was not planned when the trial was conceived. There is considerable risk with a post hoc analysis of this type. The authors statistically controlled for baseline differences between the sexes. Unfortunately, the study was not originally set up to evaluate differences by sex, and there was a disproportionate number of men. Another limitation is that it relies a great deal on statistical adjustments. There is also a risk that an association may occur by chance to multiple analyses.

* OUTCOMES MEASURED

The primary outcome was death from any cause within an average of 37 months (range 24 to 48 months). Other outcomes included death from cardiovascular disease, death from worsening heart failure, and hospitalization for heart failure.

* RESULTS

The investigators reported that women on digoxin had a significantly higher mortality compared with men (33.1% vs 35.2%, P=.034). Mortality was not significantly higher in women receiving digoxin compared with women receiving placebo (33.1% vs 28.9%, respectively; 95% confidence interval [CI], 20.5 to 8.8). However, after adjusting for other factors (eg, age, race, ejection fraction), digoxin use was associated with a significant increase in mortality in women compared with men (hazard ratio 1.23; 95% CI, 1.02-1.47; number needed to harm=22; 95% CI, 11-227).

There was no overall increase in mortality in men taking digoxin versus placebo. There was no significant difference between men and women regarding the secondary outcomes of death from cardiovascular disease or death from worsening heart failure. Higher rates of hospitalization in women with worsening heart failure approached statistical significance when compared with men (30.2% vs 25.8%, P=.053). There was no significant difference in rate of hospitalization for other causes.

Sharon See, PharmD and Patricio Bruno, DO, St. John's University, College of Pharmacy and Allied Health Professions, Jamaica, NY, and Department of Family Practice, Beth Israel Medical Center, New York, NY. E-mail: sees@stjohns.edu and patricbruno@cs.com.

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