Digitalis therapy in renal failure with special regard to digitoxin.

When prescribing cardiac glycosides for patients with renal failure, one should consider the different pharmacokinetics of the two most important glycosides, digoxin and digitoxin. Whereas steady state plasma concentrations of digoxin are altered proportionally to renal clearance of creatinine, those of digitoxin remain the same throughout a wide range of renal impairment. The steady state level of both glycosides is partly determined by several clinical factors such as dose, body weight, height, age and serum potassium. However, it is thought that bioavailability, volume of distribution, biotransformation, and total body clearance have the greatest importance for the variability of the plasma glycoside concentrations in patients with normal and with impaired renal function. The bioavailability and biotransformation of digoxin do not vary between healthy subjects and patients with renal insufficiency. As the volume of distribution is smaller in patients with severe renal failure that in normal subjects, the loading dose has to be altered. With decreasing creatinine clearance the total body clearance as well as the renal clearance of digoxin is reduced. On the basis of this assumption maintenance dosage regiments must be adjusted. For digitoxin, the four above-mentioned pharmacokinetic parameters are not altered in patients with renal failure compared to healthy subjects. Moreover, investigations dealing with this problem have suggested an altered protein binding of digitoxin and its metabolites as a possible factor in avoiding accumulation of the drug. However, it is one of the aims of this article to show that a decreased urinary excretion of digitoxin and metabolites is compensated by an increased excretion via the feces. Loading dose and maintenance dose of digitoxin do not have to be adjusted in patients with renal failure.