[Digoxin-propafenone interaction: values and limitations of plasma determination of the 2 drugs. Anti-arrhythmia effectiveness of propafenone].

: Propafenon's influence on the pharmacokinetic and actions of digitalis and viceversa have been evaluated in 27 patients (25 with ventricular hyperkinetic arrhythmias and 2 with paroxismal atrial fibrillation). Patients were divided in two groups according to whether the drug firstly administered were digoxin or propafenon. Plasmatic digoxin and/or propafenon's concentrations, these last performed only in 12 patients, were determined before and during the association and after propafenon's interruption at 7.55-9-11 and at 3-8 p.m. During drug's association area under the plasmatic digoxin concentration curve (AUC 12h) increased on the average by 13.8% (from 19.27 +/- 6.002 ng hours/ml to 21.94 +/- 6.198 ng hours/ml: P less than 0.05) and by 19% at the first hour. Neverthless individual behaviour was not homogeneous since the plasmatic digoxin concentration (PDC) increased in 22 cases (81.4%) and decreased in 5 (18.6%). In 6 patients mean increase was 38.8% (from 16.72 +/- 3.0 ng hours/ml to 23.21 +/- 5.44 ng hours/ml) without signs of digoxin intoxication. Another patient with congestive heart failure and basal PDC 1.87 ng/ml experienced digoxin poisoning with fatal ventricular fibrillation after propafenon. Digoxin administration in the second group's patients produced a not significant increase of plasmatic propafenon concentration (PPC). There was a good correlation among propafenon's absolute amount and plasmatic concentration and antiarrhythmic effect and no correlation among PPC and body-weight related dose. Propafenon's to digitalis association induced, in propafenon's steady state, significant P-R longation from 170 to 190 ms (P less than 0.01) but HR, QRS and QTc didn't show any important change (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)