Arrhythmogenic potential of dopexamine hydrochloride during halothane anaesthesia in dogs

Dopexamine hydrochloride (Dopacard®) is the novel synthetic catecholamine designed for use in the acute management of a low cardiac output status. In addition to dopaminergic receptor stimulation, dopexamine hydrochloride is a potent β₂ adrenoreceptor agonist with negligible direct β₁ and no alpha adrenergic effect. The objective of this study was to compare the arrhythmogenic effects of dopexamine hydrochloride and dopamine in dogs anaesthetized with halothane (1.2 MAC). The starting dose for dopexamine hydrochloride was 3.5 μg · kg^?1 min^?1 and for dopamine was 5 μg · 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 ventricular tachycardia when dopamine was administered in concentrations ranging between 18–20 μg · kg^?1 · min^?1. Unlike dopamine, dopexamine hydrochloride even at concentrations as high as 50 μg · kg^?1· min^?1 did not induce any atrial or ventricular ectopic beats. Lack of β_-1 and alpha adrenergic agonist effects is a likely explanation for low arrhythmogenicity of dopexamine hydrochloride. Both drugs increase cardiac output; dopexamine hydrochloride primarily by a dose-related increase in heart rate and increased aflerload. At the maximal concentration dopexamine hydrochloride increased heart rate from 114 to 150 beat · min^?1, mean arterial pressure decreased from 81 mmHg to 45 mmHg and SVR decreased from 2418 to 962 dyne · sec^?1cm^?5. Myocardial contractility increased only moderately, 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 concentration, from 1480 to 2570 mmHg · sec^?1. Dopamine also produced vasoconstriction: SVR increased from 2325 to 2683 dyne · sec · cm^?5 and mean arterial pressure from 86 mmHg to 110 mmHg. In conclusion, dopexamine hydrochloride is less arrhythmogenic than dopamine, has less of an inotropic effect, and a greater effect on aflerload.