Thermal antinociceptive effect of transdermal tramadol hydrochloride in avian

Physical restraint necessary for parenteral drug administration is inherently stressful for birds. In contrast, transdermal drug delivery offers a simpler method of administration with minimal associated stress. This study aimed to investigate the potential of transdermal delivery as a less stressful alternative route for administering tramadol hydrochloride in birds. Broiler chickens (n=24) age 85 days were used as a model for avian species in this study. The broilers were randomly allocated into four groups of six: a control group with no intervention (C); an intravenous group receiving 5mg/kg of tramadol (IV); and two transdermal groups receiving 5mg/kg (TD1) and 10mg/kg (TD2) of tramadol, respectively. To simulate pain, thermal antinociception effect was assessed using a customised cage with a temperature-controlled floor. The foot withdrawal response to thermal stimulation was recorded for each bird at baseline (pre-administration), at 30-, 60-, 120-, 240-, 360-, and 480-minute post administration. Compared to the control group, all treatment groups (IV, TD1, TD2) exhibited significantly elevated (P<0.05) foot withdrawal thermal threshold. Both TD1 and TD2 showed a significant elevation of foot withdrawal thermal threshold compared to baseline at 60- and 120-minutes following tramadol administration, while IV was statistically significant only at 60 minutes following tramadol administration. The greatest increase in foot withdrawal thermal threshold was observed at 30 minutes following intravenous tramadol administration. TD2 demonstrated the longest duration of effect, remaining effective up to 240 minutes following tramadol administration. This study is the first to assess the antinociceptive effect of transdermal tramadol in birds. Further investigation is warranted to validate its efficacy across different avian species.