The diisobutyryl ester of N-methyldopamine, ibopamine: evaluation of electrophysiological properties and arrhythmogenicity studies.

The electrophysiological properties of ibopamine (SB-7505), the 3,4-diisobutyryl ester N-methyldopamine, was evaluated in 8 patients with syncopes of unknown etiology or with suspected disease of the sinus node or due to I-II degree AV block. A complete electrophysiological examination, including atrial and ventricular stimulation, was performed both in baseline conditions and within 1 h after oral administration of ibopamine 200 mg in a single dose. The study showed a slight reduction in effective refractory periods in the right atrium (-4.26%), the atrio-ventricular node (-6.45%) and the right ventricle (-6.79%) after ibopamine. Ibopamine was not found to facilitate the occurrence of atrial and/or ventricular arrhythmias. A 24-h dynamic Holter ECG performed in baseline conditions and during administration of ibopamine 200 mg t.i.d. showed no changes in baseline heart rate, nor was any increase in the number of atrial or ventricular extrasystoles detectable. It may therefore be concluded that ibopamine, when administered at the above dosages to the patients studied, does not modify heart rate or sinus function parameters to a statistically significant extent. It also reduces effective refractory periods in the right atrium, in the atrioventricular node and in the right ventricle without inducing or facilitating the occurrence of atrial or ventricular arrhythmias.