Digitalis Glycosides toxicity

Digitalis Glycosides toxicity
Key points
• Toxic effects of digitalis glycosides (DGs) involve the central nervous system (CNS) and gastrointestinal (GI) tract as well as the cardiovascular system (CVS).
• Cardiac dysrhythmias, including both tachydysrhythmias and bradydysrhythmias.
• Markedly elevated serum digoxin and potassium levels are characteristic of DG poisoning due to acute overdose, whereas digoxin levels may be minimally elevated or even “therapeutic” and the potassium level is typically low or normal in chronic toxicity due to excessive therapeutic dosing.

Digitalis glycosides poisoning
The cardiac glycosides of therapeutic importance include digoxin, digitoxin and ouabin. These are derived from plant Foxglove (Digitalis purpurea).
Clinical uses: treatment of congestive heart failure and management of supraventricular rhythm disturbances.
Pharmacokinetics
Gastrointestinal absorption appears to result from passive diffusion. Because the rate and completeness of absorption are inversely related to molecular polarity, digoxin and ouabain, which are more polar than digitoxin, are less rapidly and less completely absorbed. Absorption also depends on pill dissolution rate, which tends to be slow and varies by manufacturer and formulation. Bioavailability is 60–85 per cent for most oral and intramuscular digoxin preparations and approaches 100 per cent for oral digitoxin, intravenous administration of digoxin.