STEADY-STATE PLASMA KINETICS OF SLOW-RELEASE PROPAFENONE, ITS 2 ISOMERS AND ITS MAIN METABOLITES

Steady-state plasma kinetics of propafenone (CAS 54063-53-5), the S- a nd R-enantiomers, and the two main metabolites were investigated in a double-blind placebo-controlled dose-finding study using a slow-releas e formulation of propafenone at three different dose regimens (2 x 225 mg, 2 x 325 mg, and 2 x 425 mg). The study included a total of 24 pat ients (18 m, 6 f) with symptomatic ventricular arrhythmia. Since stati stically valuable data was limited by a considerable portion of undete ctable plasma concentrations among patients having received verum, kin etics could be followed up only in a group of 14 patients (10 m, 4 f) over a period of 12 h under steady state conditions. All patients were phenotyped prior to the study by measuring the ratio of sparteine/deh ydrosparteine and three poor metabolizers were identified. A detailed description of the analytical methods used is given. With the low dose , a mean plasma level of 87 +/- 16 ng propafenone per ml plasma was ob tained, with the medium dose a level of 243 +/- 34 ng/ml and with the higher dose 334 +/- 71 ng/ml were reached. All three doses of the slow -release preparation resulted in a smoothened and thus therapeutically favorable plasma concentration curve, independently from phenotype. W ith regard to the two propafenone enantiomers; a preferential clearanc e of the R-form (S/R = 2.08 +/- 0.19) could be confirmed without obser ving a change in the S/R ratio with time.