The pharmacokinetics of a fentanyl matrix patch applied at three different anatomical locations in horses.

Fentanyl was rapidly absorbed and persisted in the plasma for up to 96 hours. No adverse effects of treatment on HR, RR or RT were observed. Further controlled prospective studies are needed to determine what plasma concentration, if any, of fentanyl achieves an analgesic effect in horses when administered via a transdermal patch system.