Comparative evaluation of the intravenous effect of medetomidine, tramadol and medetomidine/tramadol combination on tear production in clinically healthy donkeys (Equus asinus)

Abstract

Various ophthalmic disorders (conjunctivitis, corneal wounds, keratitis) have been reported in donkeys. There are no studies on the effect of medetomidine or tramadol on Schirmer tear test (STT) readings in donkeys. This prospective study investigated changes in STT readings in 24 clinically healthy donkeys (Equus asinus) (14 geldings and 10 mares) treated with commonly used doses of medetomidine hydrochloride and tramadol hydrochloride as mono- or combined therapy. Analgesia, sedation, ataxia, and STT readings were measured before treatment (baseline) and at different periods after administration (5–120 min) of the specific drug in each group. Tramadol monotherapy induced a mild analgesic effect (score 1) at 10 min post-administration. All treated donkeys exhibited mild to moderate ataxia. Medetomidine alone or in combination with tramadol induced a significant decrease (P<0.05) in the STT readings in both right and left eyes at 5, 15, 30, and 60 min relative to baseline, and the lowest values were observed 60 min after drug administration in both groups. Intravenous administration of medetomidine alone or in combination with tramadol induced a significant reduction in STT readings in clinically healthy donkeys. Therefore, in donkeys, the ocular surface treated with these sedatives should be carefully examined and adequately covered by an artificial tear solution or ophthalmic gel.