Lack of local anaesthetic efficacy of fentanyl in the abaxial sesamoid block model

Fentanyl and other opioid drugs have their effect in the central nervous sy stem; however, activity at peripheral sites has also been demonstrated. Pai n-suppression activity at peripheral sites raises the possibility of skille d individuals producing local anaesthetic effects with small doses of opioi d drugs that would be difficult to detect forensically and could be used to affect the outcome of a race. Therefore, the local pain-suppression effect (peripheral nerve inhibition) of fentanyl was tested using an abaxial sesa moid block/hoof withdrawal model. With this model, fentanyl did not produce significant anaesthesia when tested in eight Thoroughbred horses, This sug gests that fentanyl at this or lower doses is unlikely to reduce pain perce ption when applied directly to sensory neurons. However, the effect of fent anyl and other opioids on joint pain perception of horses, especially infla med joints, is unknown.