Isoxsuprine is a therapeutic medication used to treat navicular disease and other lower limb problems in horses and is one of the more frequently detected therapeutic agents in racing horses. In crossover studies, horses were administered intravenous and oral isoxsuprine to determine the character and duration of pharmacological effects. Following intravenous administration, isoxsuprine significantly increased heart rate, spontaneous activity, and sweat production. There was an apparent, although statistically insignificant, increase in cutaneous blood flow. Skin temperature decreased below control values, and there was a significant decrease in core temperature. Isoxsuprine also reduced smooth muscle tone. In contrast, after oral dosing, there was no statistical difference between control and isoxsuprine-treated horses for any of the measured variables. It was concluded that the measurable physiologic effects of intravenous isoxsuprine are short-lived, since none of the above responses was apparent four hours or more after intravenous administration.

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