Hypokalaemia, hypernatraemia, or hypomagnesaemia increase the toxic cardiovascular effects of Digoxin because of their depressive effects on the Na+/K+ ATPase pump.
- 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.
- Amiodarone can cause digoxin toxicity
Dose range:You must check with BNF or drug datasheet. Doses in Microgrammes 0.5 mg = 500 mcg
|Digoxin (Loading dose Fast AF but well)||500 mcg at 0 and 6 hours (2nd dose can be 250 mcg if elderly) ||stat||PO|
|Digoxin (Emergency) ||750 mcg to 1 g given slow IV over 2 hours ||stat||IV infusion|
|Digoxin (Maintenance) ||125-250 mcg ( 62.5 mcg in frail elderly) ||OD||PO|
- 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)
- 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