Name of the Cardiac Glycosides drug:
Digoxin
Mechanism of action:
- The mechanism of action of cardiac glycosides involves inhibiting the Na+, K+ ATPase enzyme, also known as the sodium-potassium pump. This causes sodium to build up inside the heart cells, decreasing the ability of the sodium-calcium exchanger to push calcium out of the cells, consequently causing calcium to build up in the sarcoplasmic reticulum. Increased intracellular calcium results in a positive inotropic effect, which in turn has the effect of increasing the force of the heart’s contractions.
- Indirectly slows conduction at SA node and AV node and centrally stimulates the vagus nerve, resulting in a negative chronotropic effect.
Indications:
- Supra ventricular Arrhythmias (atrial fibrillation and atrial flutter)
- Congestive Heart Failure
Cautions & Contraindications:
- Complete heart block and second- degree block
- Tachyarrhythmias associated with Wolf- Parkinson- white syndrome
- Ventricular tachycardia/ fibrillation
- Myocarditis/ constrictive pericarditis
- Hypertrophic cardiomyopathy
Side- Effects:
- GI disturbance
- Dizziness, hallucinations.
- Blurred or yellow vision (xanthopsia suggests toxicity)
- Arrhythmias/ conduction defects
- Rash
- Abdominal pain (suggests toxicity)
- Electrolyte Imbalance
| Digoxin |
| Availability: Oral Solution: (Lanoxin): 50 mcg/mL. Injection Solution: (Lanoxin): 100 mcg/mL, 250 mcg/mL. Tablets: (Lanoxin): 62.5 mcg, 125 mcg, 187.5 mcg, 250 mcg. |
| Administration/handling: IM rarely used (produces severe local irritation, erratic absorption). If no other route possible, give deep into muscle followed by massage. Give no more than 2 mL at any one site • IV may give undiluted or dilute with at least a 4-fold volume of Sterile Water for Injection or D5W (less may cause precipitate). • Use immediately. • Give IV slowly over at least 5 min. PO • May give without regard to food. • Tablets may be crushed. |
| Loading Dose PO: Adults, elderly: 0.75–1.5 mg. Children 10 yrs and older: 10–15 mcg/kg. Children 5–9 yrs: 20–35 mcg/kg. Children 2–4 yrs: 30–40 mcg/kg. Children 1–23 mos: 35–60 mcg/kg. Neonates, full-term: 25–35 mcg/kg. Neonates, premature: 20–30 mcg/kg. IV: Adults, elderly: 0.5–1 mg. Children 10 yrs and older: 8–12 mcg/kg. Children 5–9 yrs: 15–30 mcg/kg. Children 2–4 yrs: 25–35 mcg/kg. Children 1–23 mos: 30–50 mcg/kg. Neonates, full-term: 20–30 mcg/kg. Neonates, premature: 15–25 mcg/kg |
| Avoid doses greater than 0.125 mg/day in elderly due to decreased renal clearance |
| HF Loading dose not recommended in HF. PO: Adults, elderly: 0.125–0.25 mg once daily |
| Atrial Fibrillation Adults, elderly: Digitalizing dose (IV): Initially, 0.25–0.5 mg over several minutes. May repeat doses of 0.25 mg q6 hrs up to a maximum of 1.5 mg over 24 hrs. Maintenance dose (PO): 0.125–0.25 mg once daily. |
Metabolism and Half- Life:
Readily absorbed from GI tract. Par_x005F_x0002_tially metabolized in liver. Primarily excreted in urine. Minimally removed by haemodialysis. Half-life: 36–48 hrs (increased in renal impairment, elderly)
Monitoring:
- Check U&Es prior to initiation of treatment
- Digoxin levels should be taken 6hrs post – dose.
Drug Interactions:
- Increased risk of AV block and symptomatic bradycardia with beta blockers.
- Risk of cardiac toxicity secondary to hypokalemia with diuretics
- Plasma concentrations increased by verapamil and diltiazem.
- Plasma concentration increased by amiodarone and reduced by St. John’s wort
Nursing Considerations:
Baseline assessment:
- Assess apical pulse. If pulse is 60 or less/min (70 or less/min for children), withhold drug, contact physician.
- Blood samples are best taken 6-8 hrs after dose or just before next dose.
Intervention/evaluation:
- Monitor pulse for bradycardia, ECG for arrhythmias for 1–2 hrs after administration (excessive slowing of pulse may be first clinical sign of toxicity).
- Assess for GI disturbances, neurological abnormalities (signs of toxicity) q2–4h during loading dose (daily during maintenance).
- Monitor serum potassium, magnesium, calcium, renal function.
- Therapeutic serum level: 0.8–2 ng/mL; toxic serum level: greater than 2 ng/mL
Patient/family teaching
- Follow-up visits, blood tests are an important part of therapy.
- Follow guidelines to take apical pulse and report pulse of 60 or less/min (or as indicated by physician).
- Wear/carry identification of digoxin therapy and inform dentist, other physician of taking digoxin.
- Do not increase or skip doses.
- Do not take OTC medications without consulting physician.
- Report decreased appetite, nausea/vomiting, diarrhea, visual changes.
Important Points:
- Hypokalemia and hypercalcemia predispose to digoxin toxicity
- Narrow therapeutic index, hence, risks of toxicity
- Requires loading dose at initiation of treatment
REFERENCES
- Robert Kizior, Keith Hodgson, Saunders Nursing Drug handbook,1st edition 2024, Elsevier Publications. ISBN-9780443116070
- McGraw Hill- Drug Handbook, Seventh Edition, 2013, McGraw Hill Education Publications,9780071799430.
- April Hazard, Cynthia Sanoski, Davi’s Drug Guide for Nurses -Sixteenth Edition 2019, FA Davis Company Publications,9780803669451.
- Jones and Bartlet, Pharmacology for Nurses, Second Edition, 2020, Jones and Bartlet Learning Publications, ISBN 9781284141986.
- Nursebro.com, Search – Nursebro
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