CHARACTER AND DURATION OF PHARMACOLOGICAL EFFECTS OF INTRAVENOUS ISOXSUPRINE

Isoxsuprine is a therapeutic medication used to treat navicular diseas e and other lower limb problems in horses and is one of the more frequ ently detected therapeutic agents in racing horses, In a crossover stu dy, horses were administered isoxsuprine i.v. to determine the charact er and duration of its pharmacological effects, Isoxsuprine significan tly increased heart rate 5-150 min following injection. Unrestrained a ctivity following isoxsuprine treatment was significantly greater than control activity for 105 min after treatment. There was an apparent, although statistically nonsignificant, increased cutaneous blood flow resulting in visible water vapour and sweat production 5-60 min after administration. Initially, there was no difference in skin temperature between control and isoxsuprine treatment values; however, skin tempe rature decreased below control values 45-120 min after injection. Conc urrently, there was a significant decrease in rectal temperature refle cting a decrease in body core temperature. Using infrared thermography , a significant decrease in superficial skin temperature of the front legs occurred 30-240 min after treatment. Isoxsuprine also reduced smo oth muscle tone, which was apparent by decreased tone of the internal anal sphincter 10-180 min after treatment. It was concluded that the m easurable pharmacological effects of i.v. isoxsuprine are short lived, since none of the above responses were apparent 4 h or more after i.v . administration.