Effects of intramuscular administration of acepromazine on palmar digital blood flow, palmar digital arterial pressure, transverse facial arterial pressure, and packed cell volume in clinically healthy, conscious horses

Objective— To determine the magnitude and duration of effects of acepromazine administered intramuscularly (IM) on digital and systemic hemodynamic variables in clinically healthy horses.
Study Design— Experimental study.
Animals— Healthy adult horses (n=12).
Methods— An ultrasonic Doppler flow probe was surgically implanted around the medial palmar digital artery before the study. Catheters were inserted in the transverse facial artery, lateral palmar digital artery, and jugular vein. A treatment group (n=6) was administered 0.04 mg/kg body weight of acepromazine IM; control horses (n=6) were administered an equivalent volume of saline IM. Palmar digital blood flow, and digital and facial arterial pressures were measured at baseline and for 6 hours after administration. Venous blood was collected for measurement of packed cell volume (PCV).
Results— Horses administered acepromazine had significantly lower facial arterial pressure compared with control horses administered saline. Palmar digital arterial blood flow in acepromazine-treated horses was not significantly different from that in control horses but increased significantly post-administration, compared with the respective baseline values for acepromazine-treated horses. PCV significantly decreased in horses administered acepromazine compared with their respective baseline value.
Conclusion— IM acepromazine causes hypotension and increases palmar digital blood flow over time but the magnitude of the effect on digital blood flow was not sufficient to yield differences compared with saline-treated horses.
Clinical Relevance— IM acepromazine has a modest effect on palmar digital blood flow, facial arterial pressures and PCV in healthy horses with minimal sedation.