Inj.digoxin
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Injection Digoxin (Inj. Digoxin)
Overview
Digoxin is a cardiac glycoside extracted from Digitalis lanata. The injectable form is used when rapid digitalization is needed or oral administration is not feasible.
Brand Names: Lanoxin, Lanoxin Pediatric
Class: Antiarrhythmic agent, Positive inotrope
Class: Antiarrhythmic agent, Positive inotrope
Available Formulations
| Preparation | Concentration | Volume |
|---|---|---|
| Lanoxin Pediatric (IV) | 100 mcg/mL | 1 mL |
| Lanoxin / Generics (IV) | 250 mcg/mL | 2 mL |
Both formulations may contain propylene glycol and alcohol.
Mechanism of Action
Digoxin inhibits Na⁺/K⁺-ATPase, the enzyme that regulates intracellular Na⁺ and K⁺:
- ↑ Intracellular Na⁺ → stimulates Na⁺/Ca²⁺ exchanger → ↑ intracellular Ca²⁺
- Acts directly on cardiac muscle and indirectly via the autonomic nervous system
- Enhances central and peripheral vagal tone
Resulting Effects
- Positive inotropic effect — increased force and velocity of myocardial contraction
- Vagomimetic effect — slowing of SA node discharge, prolongation of AV nodal refractoriness
- Neurohormonal deactivation — decreases sympathetic nervous system activity
Pharmacokinetics (IV)
| Parameter | Value |
|---|---|
| Onset of action (IV) | Within minutes |
| Peak effect (IV) | 1.5–3 hours |
| Peak effect (oral) | 4–6 hours |
| Half-life | 36–48 hours |
| Elimination | Excreted unchanged by kidneys |
| Oral bioavailability (tablet) | 60–75% |
Indications
- Atrial fibrillation / atrial flutter — IV to acutely slow ventricular rate (main adult use)
- Heart failure — positive inotropic support (oral more common; IV used acutely)
- Paediatric arrhythmias — broader range than adults (SVT, AF, atrial flutter)
Note: Digoxin has largely been replaced for most SVTs by adenosine, verapamil, and beta-blockers due to slower onset and lower success rate. — Roberts & Hedges' Clinical Procedures in Emergency Medicine
Dosing
Adults — Acute IV Loading (Digitalizing)
- IV loading dose: 0.5–1.0 mg (given in divided doses)
- Initial dose: ½ of total digitalizing dose (TDD), then ¼ TDD every 4–8 hours × 2 doses
- Obtain ECG 6 hours after each dose to assess for toxicity
For Rate Control in AF (Emergency)
- IV loading: 10–15 mcg/kg, followed by individual parenteral dosing until desired rate is achieved
Chronic oral maintenance: 0.125–0.25 mg/day as a single dose (adjust for renal function)
Paediatric Digitalizing & Maintenance Doses (IV/IM) — mcg/kg/24 hr
| Age | TDD (IV/IM) | Daily Maintenance (IV/IM) |
|---|---|---|
| Premature neonate | 15 | 3–4 |
| Full-term neonate | 20 | 6–8 |
| 1 month – <2 years | 30–40 | 7.5–9 |
| 2–10 years | 20–30 | 6–8 |
| >10 years (<100 kg) | 8–12 | 2–3 |
Digitalizing schedule: Initial ½ TDD, then ¼ TDD Q8–18 hr × 2 doses; ECG 6 hr after dose.
- <10 yr: Maintenance dose ÷ BID
- ≥10 yr: Maintenance dose once daily
— The Harriet Lane Handbook, 23rd Edition
Electrophysiologic Effects
| Parameter | Effect |
|---|---|
| Sinus rate | Minimal change (may decrease in heart failure) |
| PR interval | Generally unchanged (may prolong in AV node disease) |
| QRS | Unaffected |
| QT interval | Unaffected |
| ST-T changes | Characteristic changes seen — do not indicate toxicity |
| AV nodal refractoriness | Prolonged (main antiarrhythmic mechanism) |
— Braunwald's Heart Disease
Contraindications
- Ventricular dysrhythmias / ventricular tachycardia
- WPW (Wolff-Parkinson-White) or LGL syndrome — may cause rapid ventricular response or VF
- Sinus node disease / SA node dysfunction
- AV block (2nd or 3rd degree)
- Patients with preserved LV systolic function (heart failure with preserved EF)
Cautions / Special Populations
- Renal failure — digoxin excreted unchanged by kidneys; dose reduction required (some dialysis patients need 0.125 mg every other day)
- Hypokalemia, hypomagnesemia — increase risk of toxicity
- Calcium channel blockers (verapamil, diltiazem) — may result in heart block; also raise digoxin levels
- Adenosine — enhanced depressant effects on SA and AV nodes
- Idiopathic hypertrophic subaortic stenosis, restrictive cardiomyopathy, constrictive pericarditis, amyloid heart disease — particularly susceptible to toxicity
Toxicity
Signs & Symptoms
- Cardiac: Bradycardia, AV block, dysrhythmias (PVCs, junctional rhythm, VT)
- GI: Nausea, vomiting, anorexia (often early)
- Neurological: Visual disturbances (yellow/green halos, blurred vision), confusion
Toxic Serum Level
- Therapeutic range: 0.5–2.0 ng/mL
- Toxicity more likely at >2 ng/mL (but can occur within therapeutic range with electrolyte disturbances)
Treatment of Toxicity — Digoxin Immune Fab (DigiFab)
Dosing based on amount ingested:
- TBL (mg) = mg digoxin ingested × 0.8
- # of vials = TBL ÷ 0.5
Dosing based on steady-state serum levels:
- Vials needed = (Serum digoxin [ng/mL] × weight [kg]) ÷ 100
— Harriet Lane Handbook, 23rd Edition
Drug Interactions (Key)
| Drug | Interaction |
|---|---|
| Verapamil / diltiazem | ↑ digoxin levels + AV block risk |
| Amiodarone | ↑ digoxin levels significantly |
| Quinidine | ↑ digoxin levels |
| Cholestyramine, antacids | ↓ oral absorption |
| Adenosine | Enhanced AV/SA nodal depression |
| Diuretics (↓K⁺/Mg²⁺) | ↑ toxicity risk |
Sources: Braunwald's Heart Disease (10th ed.), Roberts & Hedges' Clinical Procedures in Emergency Medicine, The Harriet Lane Handbook (23rd ed.)
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