Responses of horses to acepromazine maleate administered orally in a paste.

The effects of acepromazine maleate (ACP), given orally in a paste form, were examined in six standard-bred geldings over a 12 hour period. Three dose rates, zero (placebo paste), 0.13 mg kg-1 and 0.26 mg kg-1, given before or after feeding, were investigated. The data were divided into two sampling periods for analysis, one from zero to 120 minutes and the other from four to 12 hours. Sedation was assessed by a score (TS score) based on general appearance, anal sphincter relaxation and penile protrusion. This TS score was significantly elevated 40 minutes after dosing with ACP, irrespective of whether the horses had been fed or not. Dose rate had no significant effect on TS in the zero to 120 minute sampling period, but the TS score was significantly (P less than 0.01) higher at the higher dose rate in the four to 12 hour period. At both dose rates, the TS scores were still significantly higher than their pretreatment values 12 hours after dosing. Systolic blood pressure (SBP), measured indirectly from the coccygeal artery, haematocrit (PCV) and total plasma protein concentration (TPP) were also examined. ACP caused significant falls in SBP and PCV, but the effect was complicated by feeding. ACP given after feeding had a reduced effect on SBP and PCV. Feeding appeared to cause a rise then a fall in PCV and TPP which was superimposed upon the fall caused by ACP. There was no difference between the two dose rates of ACP on SBP and PCV.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Bioavailability of phenylbutazone preparations in the horse.

Plasma phenylbutazone concentrations were determined for up to 12 h in 6 horses following intravenous and oral phenylbutazone administration. To evaluate the bioavailability of different oral preparations, phenylbutazone was administered in a paste as well as the traditional powder form. The effect of the state of stomach contents on the absorption of phenylbutazone was investigated by administering the paste before and after feeding; the powder was given in a small bran mash and a full feed of lucerne chaff, wheaten chaff and bran. Despite great variability among individual horses both the paste form of phenylbutazone administered before a meal and the powder given in a small bran mash appeared to be almost completely absorbed, However, phenylbutazone paste administered after feeding or phenylbutazone powder given in a full feed resulted in lower peak plasma phenylbutazone levels than when administered on an empty or relatively empty stomach.