Isoxsuprine is a synthetic chemical with epinephrine-Like effects. Its action relates specifically to the walls of arteries which are located in the muscles, internal organs, and extremities. Isoxsuprine causes these arteries to dilate.
Isoxsuprine has been used in the treatment of navicular disease and laminitis, where it is presumed that the disease is associated with some degree of decreased blood supply. Isoxsuprine also has been used to relax the uterus during the treatment of uterine infections. In other species, it has been suggested that isoxsuprine can be used to attempt to treat premature labor.
Isoxsuprine is given orally in a dose ranging from 0.2 mg/kg to 0.6 mg/kg, depending on the treating veterinarian's discretion. This dose is given 2-4 times daily.
The major side effects concern the cardiovascular system. Isoxsuprine causes the systolic blood pressure (e.g., 150/100, the upper number, 150 being systolic) to rise, while the diastolic pressure falls. Reported side effects in other species include nervousness, trembling, weakness, dizziness, palpitations, nausea, and vomiting.
If the horse appears to be developing side effects, consult the veterinarian regarding advisability of stopping this medication, or changing dosage.
If a horse is receiving isoxsuprine therapy, the veterinarian must know this before treatment occurs with any anesthetic, tranquilizer, or narcotic drug.
No information is available concerning safety of isoxsuprine use during pregnancy'. Isoxsuprine is known to cause relaxation of the uterus.
ARCI: Isoxsuprine is a Class 4 drug in the ARCI uniform classification system.
Detection Time Information: Isoxsuprine can take up to 14 days or more to clear with as much as a 37-day detection time reported. It is a very common source of medication violations.
In most of my observations and experiences, when Isoxsuprine was used for horses suffering either from laminitis or navicular related lameness, I have noticed that this drug did nothing for the horses, and in addition to its relatively high price, it was nothing else but a waste of money. I believe that navicular lameness has nothing to do with the blood circulation in the hoof. In the case of laminitis it is beyond me how this drug could possibly dilate, in many cases, already damaged arteries. There are cases where the Isoxsuprine will be effective in the combination with phenylbutazone when the bute by itself is ineffective. More likely due to drug interaction.
All my comments are merely my opinions and beliefs gained from 40 years of professional life with horses. All drugs should be used only by the consent of a veterinarian and according to his instructions. A person who is with the horse everyday, should know him better than anyone else.