Treatment of congestive heart failure--current status of use of digitoxin.

摘要

Digitalis glycosides exert a positive inotropic effect, i.e. an increase in myocardial contractility associated with a prolongation of relaxation period, and glycosides lower the heart rate (negative chronotropic), impede stimulus conduction (negative dromotropic) and promote myocardial excitability (positive bathmotropic). They seem to influence the activities of both the vagal and the sympathetic systems. Digitalis glycosides that belong to different substance classes are closely comparable concerning pharmacodynamics but differ substantially in regard to pharmacokinetics. Digoxin and its derivatives are less lipophilic, show lower protein binding and shorter half-life, are mainly eliminated via the kidney and accumulate rather rapidly in cases of insufficient kidney function. Digitoxin is highly lipophilic and extensively bound to plasma proteins, has a longer half-life, is mainly eliminated in the metabolized state via urine and faeces and does not accumulate in kidney dysfunction. As a result of a more stable pharmacokinetic profile, the incidence of toxic side effects seems to be lower with digitoxin than with digoxin. Since the beginning of the 1990s, the antagonists of the RAAS qualified as the standard treatment for congestive heart failure, often in combination with diuretics, vasodilators or beta-antagonists. However, the important role of digitalis glycosides as therapeutic comedication or alternative was never denied, especially in atrial fibrillation with tachycardia. The PROVED and RADIANCE trials proved a detrimental effect of the withdrawal of digoxin therapy on exercise capacity, left-ventricular ejection fraction and clinical symptoms. The DIG trial revealed that digoxin comedication in sinus rhythm patients with congestive heart failure was associated with a lower morbidity (as taken from death or hospitalization because of worsening heart failure) and an unchanged overall mortality--being a unique feature among the available inotropic drugs. Comparable studies for digitoxin have not yet been performed but, because of its higher pharmacological stability, it might well be associated with even more advantages in this regard than digoxin.