Studies on isoxsuprine hydrochloride for the treatment of navicular disease

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 weight (bwt) twice daily for periods of six to 14 weeks. Twelve of the horses became completely sound while being treated, although two required a 50 per cent increase in dose. Nine of the horses have remained sound two to 10 months after ceasing therapy. In a controlled randomised double blind clinical trial, 16 horses with navicular disease were assigned to treatment with either a placebo paste or isoxsuprine paste for three weeks and then re-examined. All the horses treated with isoxsuprine showed improvement in gait, with seven of eight horses becoming sound, whereas only two horses treated with a placebo paste showed slight improvement. This difference in response was highly significant (P less than 0.001). To evaluate any physiological and biochemical effects of isoxsuprine, it was administered to five Standardbred geldings at dose rates of 0.6 mg/kg bwt 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, infra-red 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 to 480 mins after isoxsuprine administration. The maximum mean increase in distal limb temperature was 3.1 degrees C and this occurred 4 h after administration of the drug.