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Isoxsuprine for Veterinary Use

by Barbara Forney, VMD

Basic Information

Isoxsuprine is a mixed beta-adrenoreceptor antagonist/agonist. It causes relaxation of vascular and uterine smooth muscle. In addition to peripheral vasodilation, isoxsuprine has been shown to decrease blood viscosity and platelet adherence. Isoxsuprine is primarily used in veterinary medicine to treat or manage navicular disease in the horse. It is used in human medicine as a tocolytic agent to decrease preterm labor or abortion. The human gastrointestinal tract absorbs isoxsuprine well, but studies in the horse indicate that oral bioavailability is approximately 2.2%.


Isoxsuprine is used in horses for the management of navicular disease and laminitis. Due to the low bioavailability in the horse, treatment with oral isoxsuprine is not universally accepted, but there are veterinarians who feel it is beneficial in some cases.

Because of its demonstrated tocolytic properties in humans, some veterinarians have used isoxsuprine for the same purpose in broodmares. Its efficacy for this use has not been well-evaluated.

Side Effects

  • Side effects after oral administration are rare in the horse because of the low level of absorption. Possible side effects could include low blood pressure, increased heart rate, and possible gastrointestinal irritation.
  • Side effects after intravenous administration include hypotension, tachycardia, CNS stimulation, and sweating.


  • Isoxsuprine is a vasodilator and should not be used in mares immediately after foaling or horses that are actively bleeding.
  • Despite the low level of oral absorption, isoxsuprine can be found in a horse’s urine for many weeks after treatment is discontinued. This may be a consideration for competition horses.
  • There are no safety studies on isoxsuprine use in pregnant or lactating mares. There are no safety studies regarding the effects on semen in breeding stallions.

Drug Interactions

  • Drug interactions are unlikely with oral isoxsuprine.


  • Overdose of isoxsuprine increases the risk and severity of the above mentioned side effects.
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Therapeutic Class
Peripheral vasodilator



Navicular disease

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About the Author

Dr. Barbara Forney

Barbara Forney, VMD

Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.

She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.

Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.