ARRHYTHMOGENIC POTENTIAL OF DOPEXAMINE HYDROCHLORIDE DURING HALOTHANEANESTHESIA IN DOGS

Dopexamine hydrochloride (Dopacard(R)) is the novel synthetic catechol amine designed for use in the acute management of a low cardiac output status. In addition to dopaminergic receptor stimulation, dopexamine hydrochloride is a potent beta(2) adrenoreceptor agonist with negligib le direct beta(1) and no alpha adrenergic effect. The objective of thi s study was to compare the arrhythmogenic effects of dopexamine hydroc hloride and dopamine in dogs anaesthetized with halothane (1.2 MAC). T he starting dose for dopexamine hydrochloride was 3.5 mu g . kg(-1) . min(-1) and for dopamine was 5 mu g . kg(-1) . min(-1). Concentrations of the drugs were increased until four or more premature ventricular contractions within 15 seconds were produced. All dogs developed ventr icular tachycardia when dopamine was administered in concentrations ra nging between 18-20 mu g . kg(-1) . min(-1). Unlike dopamine, dopexami ne hydrochloride even at concentrations as high as 50 mu g . kg(-1) . min(-1) did not induce any atrial or ventricular ectopic beats. Lack o f beta(1) and alpha adrenergic agonist effects is a likely explanation for low arrhythmogenicity of dopexamine hydrochloride. Both drugs inc rease cardiac output; dopexamine hydrochloride primarily by a dose-rel ated increase in heart rate and increased after load. At the maximal c oncentration doper amine hydrochloride increased heart rate from 114 t o 150 beat . min-1, mean arterial pressure decreased from 81 mmHg to 4 5 mmHg and SVR decreased from 2418 to 962 dyne . sec(-1) cm(-5). Myoca rdial contractility increased only mod erately, as evaluated by dP/dt, which increased from 1290 to 1696 mmHg . sec(-1). Dopamine had a more marked inotropic effect: the dP/dt increased, at the maximal concentr ation, from 1480 to 2570 mmHg . sec(-1). Dopamine also produced vasoco nstriction: SVR increasedfrom 2325 to 2683 dyne . sec . cm(-5) and mea n arterial pressure from 86 mmHg to 110 mmHg. In conclusion, dopexamin e hydrochloride is less arrhythmogenic than dopamine, has less of an i notropic effect, and a greater effect on afterload.