CC Pharm | Digoxin

Lanoxin (Digoxin) 80/20 Clinical Summary

1. Expected Action & Mechanism

• Positive Inotrope: Inhibits the Na+/K+-ATPase pump1, raising intracellular sodium. This reverses sodium-calcium exchange to increase intracellular calcium, boosting myocardial contractility, force, and velocity12.
• Negative Chrono/Dromotrope: Increases vagal activity, slowing AV nodal conduction and prolonging refractory period to slow ventricular rate3.

2. Therapeutic Use & Selection

• Indicated for heart failure (HF) and controlling ventricular rate in chronic atrial fibrillation (AF)4. Off-label for fetal supraventricular tachyarrhythmias5.
• Benefit: Boosts cardiac output, lowers sympathetic tone/heart rate, and causes diuresis2. Beta-blockers, verapamil, and diltiazem are replacing it for AF rate control13. Does not convert acute AF to sinus3.

3. Crucial Administration Protocols

• IV: Preferred (IM causes severe pain)67. Dilute 1 mL in $\ge$4 mL sterile water, 0.9% NaCl, or D5W to prevent precipitation8. Inject slowly over $\ge$5 minutes to avoid sudden vasoconstriction8.
• Oral (PO): Tablet bioavailability is 60–80% (solution 70–85%)910. High-fiber meals decrease absorption910.

4. Dosing & Renal Safety Guidance

• Dosing must be based on lean body weight (LBW), efficacy, and serum levels4.
• Geriatric: PIM (avoid first-line); if used, limit to 125 mcg/day to reduce toxicity risk1112.
• Renal GFR Adjustments (Half-life 36–48h)13:
  • >50 mL/min: No adjustment14.
  • 10–50 mL/min: Give 25%–75% of dose every 36h14.
  • <10 mL/min: Give 10%–25% of dose every 48h14.
  • Dialysis: Not removed by dialysis15.

5. Adverse Reactions & Toxicity

• Severe Risks: AV block, bradycardia, VT/VF, cardiac arrest, hyperkalemia, bowel ischemia/necrosis1617.
• Toxicity Signs: Blurred/yellow vision (xanthopsia), GI distress (nausea, vomiting, anorexia), and CNS changes (confusion, delirium, hallucinations)16more_horiz.

6. Priority Nursing Pearls (The 20% to Know)

• Monitoring: Track heart rate (bradycardia risk)16, toxicity, and clinical efficacy4.
• Labs: Monitor GFR/CrCl, potassium (hypokalemia is an adverse reaction; hyperkalemia occurs in toxicity), and digoxin levels16more_horiz.
• Interactions: Digoxin is a P-gp substrate; P-gp inhibitors/inducers trigger drug interactions13. WPW use increases ventricular response risk4.