Digoxin

Digoxin is a cardiac glycoside used in the treat of atrial arrhythmias and in cardiac failure as a positive inotrope.

Digoxin has both a direct and indirect mechanism of action:

Direct
Inhibits cardiac Na⁺/K⁺ ATPase, causing:
- Increasing intracellular [Na⁺], decreasing activity of the Na⁺/Ca²⁺ pump
- Increased intracellular Ca²⁺ increases inotropy
- Decreased K⁺ results prolongs refractory period of the AV node and bundle of His
Indirect
Parasympathomimetic effects by increasing ACh release at cardiac muscarinic receptors. This is due to sensitisation of baroreceptors, and increased vagal output from the nucleus of tractus solitarius
- Slows AV nodal conduction and ventricular response
  This improves coronary blood flow, increasing time for ventricular filling, and improving cardiac output.

Property	Action
Class	Cardiac Glycoside
Uses	Arrhythmia - particularly AF/Flutter, and CCF
Presentation	Tablets, elixir, clear colourless solution
Route of Administration	PO/IV
Dosing	PO: 62.5μg-250μg, IV: 250-500μg load
Absorption	>70% bioavailability though varies with formulation
Distribution	25% protein bound. V_D 5-11L.kg^-1, dependent on lean mass
Metabolism	Minimal hepatic metabolism
Elimination	Renal elimination of active metabolites t_1/2 35 hours - increased in renal failure
CVS	↓ HR, ↑ inotropy, arrhythmias including; bigeminy, PVCs, 1^st/2^nd/3^rd degree AV block, SVT, VT
CNS	Deranged red-green colour perception, visual disturbances, headache
Immune	Eosinophilia and rash
Metabolic	Gynaecomastia
Toxic Effects	Narrow TI. Severe arrhythmia with DC cardioversion

Interaction	Drug
Increased level	Amiodarone, captopril, erythromycin, verapamil
Decreased level	Antacids, cholestyramine, phenytoin, metoclopramide

References

Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.

Last updated 2020-11-10