Comparative Effect of Intravenous Administration of Medetomidine, Tramadol, and Medetomidine/Tramadol Combination on Intraocular Pressure (IOP) in Clinically Healthy Donkeys (Equus asinus)

In this study, an analysis of the comparative effect of intravenous medetomidine, tramadol, and medetomidine combined with tramadol on the intraocular pressure in donkeys was conducted. In an experimental randomized prospective study, 24 adult donkeys devoid of ophthalmic defects were allocated randomly into four groups (six each). The first group received medetomidine hydrochloride (MED) intravenously at 0.007 mg kg−1, and the second group received tramadol hydrochloride (TRA) at 2 mg kg−1. The third group received a combination of MED and TRA at the same dose rates. However, the fourth group received 10 mL of 0.9% normal saline. Intraocular pressure values, heart rate, respiratory rate, and body temperature were measured before treatment (T0) and at 5, 15, 30, 45, 90, and 120 minutes after treatment. Donkeys treated with MED alone or MED/TRA combination exhibited a significant (P < .05) decrease in heart rate and respiratory rate at T5 until T90 compared with tramadol and normal saline. Intraocular pressure significantly (P < .001) decreased in donkeys treated with MED or MED/TRA combination in comparison with TRA and normal saline at T5 to T90. The highest reduction in IOP values in both treated groups was observed at T30 in the right and left eyes ([11.30 ± 0.94 and 10.59 ± 0.51 mmHg, MED groups, respectively] and [12.80 ± 0.65 and 12.30 ± 0.58 mmHg, MED/TRA groups, respectively]). In conclusion, medetomidine alone or in combination with tramadol could decrease the IOP values in healthy donkeys. Therefore, it may be used safely as a preoperative analgesic for intraocular surgery.