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Digitalis – Effects, Uses and Side Effects

Digitalis refers to heart-active compounds derived from the foxglove plant, used to treat heart failure and certain cardiac arrhythmias.

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Things worth knowing about "Digitalis"

Digitalis refers to heart-active compounds derived from the foxglove plant, used to treat heart failure and certain cardiac arrhythmias.

What is Digitalis?

Digitalis is a collective term for cardiac glycosides originally derived from plants of the genus Digitalis, commonly known as foxglove. The most well-known compounds are digoxin and digitoxin. These substances are among the oldest known heart medications and have been used in medicine since the 18th century. Today, they are primarily recognized for treating chronic heart failure and arrhythmias such as atrial fibrillation.

Mechanism of Action

Cardiac glycosides work by inhibiting the sodium-potassium ATPase enzyme in heart muscle cells. This inhibition leads to an increase in intracellular sodium, which in turn raises intracellular calcium levels. The result is a stronger, more efficient contraction of the heart muscle -- an effect known as positive inotropy.

At the same time, digitalis slows conduction through the atrioventricular (AV) node, reducing heart rate. This is referred to as a negative chronotropic and negative dromotropic effect, which is particularly valuable in managing atrial fibrillation.

Indications

Chronic heart failure: Digitalis improves the pumping function of the heart and can relieve symptoms such as shortness of breath and fluid retention.
Atrial fibrillation: By slowing AV conduction, it helps control ventricular rate.
Atrial flutter: Similar use as in atrial fibrillation for rate control.

Dosage and Treatment Guidance

Cardiac glycosides have a narrow therapeutic index, meaning the difference between an effective and a toxic dose is small. Dosage must therefore be individually adjusted and carefully monitored. Regular blood level checks (serum digoxin levels) and potassium monitoring are essential, as low potassium (hypokalemia) significantly increases the risk of toxicity.

The typical therapeutic serum concentration of digoxin for heart failure is 0.5 to 0.9 ng/mL. Special caution is required in elderly patients and those with impaired kidney function, as drug elimination may be slowed.

Side Effects

Side effects often occur with overdose and are referred to as digitalis toxicity. Common signs include:

Nausea, vomiting, and loss of appetite
Cardiac arrhythmias (e.g., AV block, ventricular extrasystoles)
Visual disturbances (yellow or green tinting of vision, blurred vision)
Confusion and headache
Weakness and fatigue

In cases of severe poisoning, the antidote digoxin-specific antibody fragments (DigiFab) is available.

Drug Interactions

Cardiac glycosides can interact with numerous other medications:

Diuretics: Can cause potassium depletion, increasing the risk of digitalis toxicity.
Amiodarone, verapamil, quinidine: Increase serum digoxin levels.
Antacids and cholestyramine: May reduce the absorption of digitalis compounds.
St. John's Wort: Can lower digoxin levels and reduce its effectiveness.

Contraindications

Second- or third-degree AV block (without a pacemaker)
Hypertrophic obstructive cardiomyopathy
Known hypersensitivity to cardiac glycosides
Wolff-Parkinson-White syndrome

References

Ponikowski P et al. - 2016 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. European Heart Journal, 2016.
Brunton LL, Knollmann BC (eds.) - Goodman & Gilman's The Pharmacological Basis of Therapeutics, 13th edition, McGraw-Hill, 2017.
Digitalis Investigation Group - The effect of digoxin on mortality and morbidity in patients with heart failure. New England Journal of Medicine, 1997; 336(8):525-533.

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