Digoxin

Hypokalaemia, hypernatraemia, or hypomagnesaemia increase the toxic cardiovascular effects of Digoxin because of their depressive effects on the Na⁺/K⁺ ATPase pump.

About : Always check the BNF link here

• Several forms exist (digitoxin, ouabain) but the commonest used in the UK is Digoxin.
• The Main indication is rate control in AF

Mode of action

• Inhibits membrane bound Na/K ATPase pump
• Leads to increased intracellular calcium - acts as an inotrope
• Also controls the ventricular rate at rest but not so much on exercise
• In excess or with hypokalaemia can cause increased automaticity and arrhythmias

Indications/Loading Doses in Microgrammes 0.5 mg = 500 mcg

• Emergency AF rate control: Load:Digoxin 750 mcg - 1 mg IV infusion over 2 hours
• Stable patient Fast AF: Digoxin 0.5 mg PO + 500 mcg PO 6-12 hours later
• Standard dosing CCF/AF at 62.5 to 250 mcg per day.
• IV to oral transition: Note Digoxin 125 mcg PO= 80 mcg IV.

Interactions

• Amiodarone can cause digoxin toxicity

Dose range:You must check with BNF or drug datasheet. Doses in Microgrammes 0.5 mg = 500 mcg

Contraindications

• Avoid Hypokalaemia and check Digoxin levels 6 hrs after an oral dose or 4 hours after IV dose
• Half life 36-48 hours but this is prolonged of there is impaired renal clearance
• WPW and AF, Amyloid heart disease, Hypertrophic cardiomyopathy
• Conduction disturbance e.g. Heart Block or Bradycardia
• WPW causing anterograde conduction of AF down the accessory pathway
• Caution in renal failure, elderly (reduced GFR and muscle mass)

Side effects

• Nausea, vomiting, Diarrhoea, Fatigue, Confusion
• Abdominal pain and even psychosis, yellow tinge to vision
• Arrhythmias - any but classically Multifocal atrial tachycardia, atrial and ventricular ectopics, Ventricular tachycardia, Ventricular fibrillation, second and 3rd-degree heart block, asystole
• In overdose treat hypokalaemia and consider Fab antibodies to Digoxin [DIGIBIND].
• In overdose Pacemaker may be needed for bradyarrhythmias.
• Classically Phenytoin and Lidocaine have been used to treat associated VT/VF
• ST/T changes can cause a false positive exercise stress test

Toxicity more common with

• Give half this dose if elderly or low muscle mass. Avoid in renal failure.
• Ensure Serum levels: 1-2 mcg/L at 6 h post dose after 7 days. Ensure K levels >4 mmol/L.
• Low Body muscle mass, Elderly patients, Renal failure, Hypokalaemia, Hypomagnesaemia
• Hypernatraemia, Hypothyroid, Amyloid heart disease

References

• Digoxin in BNF