6.7 Cardiac Glycosides
Digoxin
Digoxin is a cardiac glycoside medication that has been used for centuries to treat heart failure. It has three effects on heart muscle: positive inotropic action (increases contractility, stroke volume and, thus, cardiac output), negative chronotropic action (decreases heart rate), and negative dromotropic action (decreases conduction of cardiac cells).[1]
Mechanism of Action: Digoxin works by inhibiting the sodium and potassium pump, which results in an increase in intracellular sodium and an influx of calcium into cardiac cells, causing the cardiac muscle fibers to contract more efficiently and increase cardiac output.[2]
Indications: This medication is used as second-line treatment for clients who have heart failure or atrial fibrillation. Due to the risk for digoxin toxicity, the clinical use of digoxin has decreased and alternative, safer medications are being used.
Nursing Considerations: Apical pulse should be taken for a full minute before administration of this medication. If the apical pulse is less than 60, the dose should be withheld, and the prescribing provider notified.
Serum digoxin levels should be monitored, with a normal therapeutic range from 0.8 to 2 ng/mL.
Serum potassium levels should also be closely monitored for clients on digoxin because hypokalemia increases the effect of digoxin and can result in digoxin toxicity. Normal potassium level is 3.5 to 5.0 mEq/L, and a result less than 3.5 should be immediately reported to the provider.
Nurses should closely monitor for signs of digoxin toxicity. Geriatric clients have an increased risk for developing digoxin toxicity. Digibind is used to treat digoxin toxicity.
Side Effects/Adverse Effects: Overdose or accumulation of digoxin causes digoxin toxicity. Signs and symptoms of digoxin toxicity are bradycardia (heart rate less than 60), nausea, vomiting, visual changes (halos), and arrhythmias. Cardiotoxicity is a serious adverse effect with ventricular dysrhythmias. Toxicity of this medication typically occurs at greater than 2 ng/mL, but some clients may have signs and symptoms at lower levels. Pediatric clients typically present with bradycardia or arrhythmias if toxicity is occurring.
Decreased renal function, hypokalemia, hypercalcemia, and hypomagnesemia may increase risk for digoxin toxicity.
Common side effects include GI symptoms, headache, weakness, dizziness, anxiety, depression, delirium, and hallucination.[3]
Health Teaching & Health Promotion The client should be instructed to follow the prescribed dosing regimen and take medications at the same time each day. The client should be cautious not to double up on medication doses. Additionally, the client should consult the health care provider if two or more doses of medication are missed for follow-up instruction.
Clients should receive health teaching regarding pulse rate monitoring and report any pulse rate less than 60. If the client experiences signs of digoxin toxicity, this should