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Digoxin - other side effects?

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phillip6103 18 Sep 2009

Adverse effects of Digoxin

The occurrence of adverse drug reactions is common, owing to its narrow therapeutic index (the margin between effectiveness and toxicity). Adverse effects are concentration-dependent, and are rare when plasma digoxin concentration is <0.8 μg/L. They are also more common in patients with low potassium levels (hypokalemia), since digoxin normally competes with K+ ions for the same binding site on the Na+/K+ ATPase pump.

Common adverse effects (≥1% of patients) include: loss of appetite, nausea, vomiting, diarrhea, blurred vision, visual disturbances (yellow-green halos), confusion, drowsiness, dizziness, nightmares, agitation, and/or depression, as well as a higher acute sense of sensual activities. Less frequent adverse effects (0.1%–1%) include: acute psychosis, delirium, amnesia, shortened QRS complex, atrial or ventricular extrasystoles, paroxysmal atrial tachycardia with AV block, ventricular tachycardia or fibrillation, heart block but when systematically sought, the evidence for this is equivocal. The pharmacological actions of digoxin usually results in electrocardiogram (ECG) changes, including ST depression or T wave inversion, which do not indicate toxicity. PR interval prolongation, however, may be a sign of digoxin toxicity. Additionally, increased intracellular Ca2+ may cause a type of arrhythmia called bigeminy (coupled beats), eventually ventricular tachycardia or fibrillation. The combination of increased (atrial) arrhythmogenesis and inhibited atrio-ventricular conduction (for example paroxysmal atrial tachycardia with A-V block - so-called "PAT with block") is said to be pathognomonic (i.e. diagnostic) of digoxin toxicity.

An often described but rarely seen adverse effect of digoxin is a disturbance of colour vision (mostly yellow and green colour) called xanthopsia. It has been proposed that the painter Vincent Van Gogh's "Yellow Period" may have somehow been influenced by concurrent digitalis therapy.

Digoxin plasma concentrations may increase while on antimalarial medication hydroxychloroquine(based on two case reports from 1982).

In overdose, the usual supportive measures are needed. If arrhythmias prove troublesome, or malignant hyperkalaemia occurs (inexorably rising potassium level due to paralysis of the cell membrane bound ATPase-dependent Na/K pumps), the specific antidote is antidigoxin (antibody fragments against digoxin, trade names of Digibind and Digifab). Toxicity can also be treated with higher than normal doses of potassium. Digoxin is not removed by hemo or peritoneal dialysis with enough effectiveness to treat toxicity.

Digoxin has potentially dangerous interactions with verapamil, amiodarone, erythromycin, and epinephrine (as would be injected with a local anesthetic).

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