Overview
Digoxin is a cardiac glycoside medication primarily used to treat heart failure and certain types of irregular heartbeats, particularly atrial fibrillation. It helps the heart beat stronger and with a more regular rhythm, improving blood circulation throughout the body.

Mechanism of Action
It works by inhibiting the sodium-potassium ATPase pump in myocardial cells. This leads to an increase in intracellular sodium, which in turn causes an accumulation of intracellular calcium via the sodium-calcium exchanger. The increased calcium enhances the contractility of the heart muscle (positive inotropic effect). It also increases vagal tone, slowing the heart rate (negative chronotropic effect).

Dosage and Administration
The dosage must be carefully individualized based on the patient’s age, lean body weight, and renal function. A typical maintenance dose ranges from 0.125 mg to 0.25 mg once daily. Due to its narrow therapeutic index, regular blood tests are required to monitor digoxin levels and prevent toxicity.

Side Effects
Side effects are often signs of toxicity and include nausea, vomiting, loss of appetite, visual disturbances (such as blurred or yellow vision), confusion, and potentially fatal arrhythmias. Hypokalemia (low potassium) significantly increases the risk of digoxin toxicity.

Contraindications
It is contraindicated in patients with ventricular fibrillation, certain types of heart block without a pacemaker, or known hypersensitivity to digoxin. Extreme caution is needed in patients with renal impairment, as the drug is primarily excreted by the kidneys.

Pregnancy and Lactation
Digoxin crosses the placenta, but it has been used during pregnancy to treat fetal and maternal arrhythmias without significant adverse effects. It is excreted in breast milk in very small amounts, and is generally considered compatible with breastfeeding.