[Dose-effect relation of N-prajmalium bitartrate with control of plasma levels].

15 patients with ventricular ectopic beats classified to at least Lown class III with more than 100 ventricular ectopic beats in one hour were treated with N-prajmalium bitartrate (NPAB) in increasing dosages. The first dosage of 4 X 5 mg/d has been increased by 5 mg in three steps of three days to a level of 4 X 20 mg/d. A resting ECG, the systolic time intervals and a 24 h ECG were registered before treatment and after every dose. The median PQ time increased from 170 msec to 200 msec, the increase becoming significant (p less than 0.05) with a dose of 4 X 5 mg/d NPAB and above. Frequency, QRS and the frequency-corrected QT time did not change significantly. At a dose of 4 X 10 mg/d NPAB the increase of the quotient pre-ejection period to ejection time PEP/LVET became significant, increasing continuously from 0.35 to 0.48. Six of the 15 patients showed a significant reduction of ventricular ectopic beats, couplets and salvoes. In two patients the antiarrhythmic effect was significant at 4 X 5 mg/d. With an increasing dose from 4 X 10 mg/d each responder showed a significant reduction of ventricular ectopy. The lowest effective plasma concentrations ranged from 15 to 213 ng/ml with a median value of 58 ng/ml and an upper quartile of 94 ng/ml. There was no significant difference in plasma concentrations between responders and non-responders.