Analgesia effects of detomidine HCl when administered into the distal interphalangeal joint in horses with experimental solar pain

Stimulation of the sympathetic nervous system, acting through the release of noradrenaline, influences the nociceptor activity that develops after tissue surgery. The alpha-2 adrenergic agonist detomidine produces analgesia through a central mechanism but also inhibits noradrenaline release at terminal nerve fiber endings. Detomidine may induce analgesia when administered at peripheral sites (eg, at the joint cavity or around the nerves). An experimental lameness was induced in the toe region of the left forelimb in 6 adult horses to test the analgesic effects of detomidine at a peripheral site. Lameness was induced by creating pressure on the dorsal margin of the sole with the help of set-screws that were screwed into a nut, then welded to the inside of each branch of the shoe. Gaits were recorded on videotape before and after application of the screws and after application of either detomidine HCl or saline into the distal interphalangeal (DIP) joint. The gaits were evaluated independently by 2 blinded clinicians and scored. Lameness scores were high after application of the screws and remained high after the administration of saline but decreased significantly (P < .05) after administration of detomidine HCl. It was concluded that detomidine HCl produces analgesia by intrasynovial administration in horses in a similar fashion as local anaesthetic agents and thus may be a good alternative for these.