[Determinants of plasma digoxin and digitoxin concentrations in elderly patients. A multivariate analysis].

In 1063 patients (greater than or equal to 60 years, 531 men, 532 women) the plasma concentration during digitalis maintenance therapy (metildigoxin, n = 356, beta-acetyldigoxin, n = 359, and digitoxin, n = 348) was determined and related to sex, age, body weight, serum potassium, renal function and the prescribed daily maintenance dose. Classification of treatment groups according to renal function (Crea less than or equal to 1.3 mg/dl parallel greater than 1.3 mg/dl) did not show any difference of the mean maintenance doses. In multiple linear regression analyses only a weak relationship between plasma digitalis concentration and the studied variables was found, which could be equally attributed to dose, creatinine and serum potassium in the digoxin derivative groups, whereas for digitoxin only body weight had a significant effect on the plasma concentration. During a maintenance dose of 0.07 or 0.1 mg/die which was given to 87% of patients in the digitoxin group, 70% were found to have plasma levels within the therapeutic range.