Isoxsuprine hydrochloride in the horse: a review.

The article reviews the use and effectiveness of Isoxsuprine hydrochloride as a treatment for navicular syndrome and laminitis in horses. The authors conclude that despite some potentially beneficial properties, its effectiveness is questionable due to factors such as poor bioavailability and lack of cardiovascular effects with oral use.

Properties and Use of Isoxsuprine Hydrochloride

• The drug has a dual action, working as both a beta-adrenoreceptor antagonist and agonist. This causes vasodilation (expansion of blood vessels), uterine relaxation, and also reduces blood viscosity and platelet aggregation.
• Isoxsuprine has been suggested for the treatment of horse ailments like navicular syndrome and laminitis, both of which are conditions that affect the hooves and can cause significant pain and lameness.

Pharmacokinetic Properties of Isoxsuprine

• When administered intravenously (i.v.), the drug has a short plasma half-life of fewer than 3 hours. This means the quantity of the drug reduces by half in the bloodstream in less than 3 hours from administration.
• The cardiovascular effects of the drug diminish quickly after i.v. administration but are absent when taken orally.
• Oral bioavailability (the rate and amount at which the active ingredient or therapeutic effect of a drug becomes available) is low at just 2.2%.
• The drug has a high first pass effect, meaning a significant portion of the drug is metabolized before it reaches systemic circulation.
• Isoxsuprine shows an apparent affinity for melanin, which may contribute to its extended excretion via the kidneys.

Efficacy of Isoxsuprine

• Clinical trials seem to support the use of isoxsuprine for treating navicular disease, but the evidence is described as ‘superficial’.
• Due to its poor oral bioavailability, lack of cardiovascular effects following oral consumption, and new evidence about the development of navicular syndrome, the research raises questions about the efficacy and practicability of isoxsuprine for handling navicular syndrome or laminitis in horses.
• The researchers conclude that the use of this drug for such conditions is questionable.