Influence of medetomidine, acepromazine, fentanyl and butorphanol on intraocular pressure and pupil size in healthy dogs

The aim of this study was to assess the effects of four different drugs used for anaesthesia premedication on intraocular pressure and pupil size in dogs. A prospective, randomised, double-blind clinical study was carried out. The subjects were forty client-owned healthy dogs (20 males and 20 females), aged 8.0 ± 2.9 years, with body weights of 11.8 ± 8.5 kg (mean ± SD) and without ocular abnormalities that were scheduled for periodontal treatment. Animals were randomly allocated into four groups and received intravenously either medetomidine 0.01 mg/kg, acepromazine 0.02 mg/kg, fentanyl 0.01 mg/kg or butorphanol 0.2 mg/kg. Intraocular pressure, pupil size, heart rate, respiratory frequency and systolic and diastolic arterial pressures were measured prior to (baseline) and at five and 10 minutes after premedication (T5, T10). Data were analysed by Anderson-Darling, Bartlett's, ANOVA and Dunnett's tests (P < 0.05). Significant increases of intraocular pressure were observed at T5 and T10 in the fentanyl group. Significant decreases of pupil size at T5 and T10 were detected in the fentanyl, butorphanol and medetomidine groups. In the fentanyl group, heart rate dropped significantly at T10, while respiratory frequency was elevated at T5 and T10. In the medetomidine group, heart rate and respiratory frequency were decreased at T5 and T10. In the butorphanol group, systolic arterial pressure was decreased at T5 and diastolic arterial pressure was decreased at T5 and T10. In the acepromazine group, systolic arterial pressure was decreased at T10. Within ten minutes after intravenous administration in healthy dogs, fentanyl significantly increased intraocular pressure and fentanyl, butorphanol and medetomidine decreased pupil size.