Studies on isoxsuprine hydrochloride for the treatment of navicular disease

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Abstract
A peripheral vasodilating agent, isoxsuprine hydrochloride, administered as an oral paste, was evaluated to determine its efficacy for the treatment of navicular disease. In a clinical trial, 13 horses with navicular disease were treated at a dose rate of 0.6 mg/kg body wt (bwt) twice daily for periods of 6-14 wk. Twelve of the horses became completely sound while being treated, although 2 required a 50% increase in dose. Nine of the horses remained sound 2-10 mo. after ceasing therapy. In a controlled randomized double blind clinical trial, 16 horses with navicular disease were assigned to treatment with eiter a placebo paste or isoxsuprine paste for 3 wk and then re-examined. All the horses treated with isoxsuprine showed improvement in gait, with 7 of 8 horses becoming sound, whereas only 2 horses treated with a placebo paste showed slight improvement. This difference in response was highly significant (P < 0.001). To evaluate any physiological and biochemical effects of isoxsuprine, it was administered to 5 Standardbred geldings at dose rates of 0.6 and 1.2 mg/kg bwt. Complete blood counts, routine plasma biochemical parameters, cardinal signs and blood pressure measurements were performed up to 24 h after a single dose. No significant change in any of these parameters was found. To assess the peripheral vasodilatory action of isoxsuprine, IR thermography of the lower limb was performed before and up to 8 h after administration to horses. This revealed a significant increase in distal limb temperature which occurred from 90-480 min after isoxsuprine administration. The maximum mean increase in distal limb temperature was 3.1.degree. C and this occurred 4 h after administration of the drug.
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