Comparison of the Sedative and Antinociceptive Effects of Midazolam and Diazepam in Horses (comparação Dos Efeitos Sedativos E/ou Antinociceptivos Do Midazolam E Diazepam Em Eqüinos)

The aim of this study was to evaluate the antinociceptive and sedative effects of midazolam and diazepam in 10 Thoroughbred mares. The sedative effects of midazolam (0.05, 0.1 and 0.15 mg/kg iv) and diazepam (0.05, 0.15 and 0.25mg/kg iv) were investigated by determination of the spontaneous locomotor activity (SLA) in automated behavior stalls and by measuring the head ptosis (HP). The antinociceptive effect was determined using a heat-projecting lamp by measuring the hoof withdrawal reflex latency (HWRL) and the skin twich reflex latency (STRL). The differences were evaluated by Tukey’s test (p < 0.05). A significant increase in SLA was observed only for diazepam at a dose of 0.05 mg/ kg, in comparison to control (saline). Midazolam decreased the head height (p<0.05), leading to sedation between 5 and 75 min after drug administration. Diazepam showed a maximum antinociceptive effect (>10 sec) in all animals tested at a dose of 0.15 mg/kg, within 5 min. Midazolam produced a good sedative effect and diazepam a short acting antinociceptive effect.