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The effects of aprindine hydrochloride, an antiarrhythmic drug of the class IB, on heart rate variability were evaluated in 13 patients (eight men and five women), ages 76 ± 11 years, who showed a standard deviation of the R-R interval measured at 5-minute intervals (SDANN) of ⩽100 msec on 24-hour electrocardiograms. After 24-hour electrocardiograms were recorded during the control period, aprindine was administered at a dose of 60 mg/day. After 2 weeks of treatment 24-hour electrocardiograms were again recorded. The SDANN was ⩽100 msec (mean, 69.3 ± 17.0 msec) in all patients during the control period, but increased after aprindine administration (mean, 86.1 ± 31.5 msec, P

Aprindine hydrochloride was administered orally to 10 patients with ventricular premature contractions in dosages of 10mg and/or 20mg at intervals of 8 hours. Plasma concentration was analyzed to clarify the process of reaching the steady state and the subsequent elimination state. The plasma concentration reached steady statewithin one to two weeks. There were very little diurnal and day-to-day variations in the plasma concentration, so a stable therapeutic level was maintained. Increased dosages from 30 to 60 mg per day resulted in threefold plasma concentration increase from 0.28 to 0.89μg/ml in steady state. The decline of aprindine hydrochloride after the last dose deviated from first-order kinetics, showing a convex decreasing curve on semilogarithmic graph paper.These results demonstrate nonlinear pharmacokinetics for aprindine hydroch loride.