Digoxin

Digoxin - a cardiac glycoside with both anti-arrhythmic and inotropic properties. Digoxin is useful for controlling the ventricular response in AF and atrial flutter. Heart failure may also be improved. It is principally excreted unchanged by the kidney and will therefore accumulate in renal impairment.

Uses
SVT

Contraindications
Intermittent complete heart block
Second-degree AV block
WPW syndrome
Hypertrophic obstructive cardiomyopathy
Constrictive pericarditis

Administration
Digoxin: conversion factor from oral to IV = 0.67 i.e. 125 μg PO = 80 μg IV

• IV loading dose: 0.5–1.0 mg in 50 ml glucose 5% or sodium chloride 0.9%, given over 2 hours
• Maintenance dose: 62.5–250 μg daily (renal function is the most important determinant of maintenance dosage)
CC 10–20 ml/min, i.e. 125–250 μg per day.
CC _ 10 ml/min, i.e. 62.5 μg on alternate days or 62.5 μg daily

Monitor:
• ECG
• Serum digoxin level

How not to use digoxin:
IM injections not recommended

Adverse effects:
Anorexia, nausea, vomiting
Diarrhoea, abdominal pain
Visual disturbances, headache
Fatigue, drowsiness, confusion, delirium, hallucinations
Arrhythmias – all forms
Heart block

Cautions:
Absorption from oral administration reduced by sucralfate and ion-exchange resins, colestyramine and colestipol Hypokalaemia and hypomagnesaemia increase the sensitivity to digoxin, and the following drugs may predispose to toxicity:

• amphotericin
• B2 sympathomimetics
• corticosteroids
• loop diuretics
• thiazides

Hypercalcaemia is inhibitory to the positive inotropic action of digoxin and potentiates the toxic effects Plasma concentration of digoxin increased by:

• amiodarone
• diltiazem
• nicardipine
• propafenone
• quinidine
• verapamil

Digoxin toxicity (DC shock may cause fatal ventricular arrhythmia) – stop digoxin at least 24 h before cardioversion B-Blockers and verapamil increase AV block and bradycardia Suxamethonium predisposes to arrhythmias

Organ failure:
Renal: toxicity – reduce dose, monitor levels

Renal replacement therapy:
CVVH not dialysed, dose as in CC 10–20 ml/min, i.e. 125–250 μg per day. Dose according to measured plasma levels. HD and PD not dialysed, dose as in CC <10 ml/min, i.e. 62.5 μg on alternate days or 62.5 μg daily; monitor levels.