Effect of medetomidine-butorphanol and dexmedetomidine-butorphanol combinations on intraocular pressure in healthy dogs.

OBJECTIVE: To assess the effects of intravenous (IV) medetomidine-butorphanol and IV dexmedetomidine-butorphanol on intraocular pressure (IOP). STUDY
DESIGN: Prospective, randomized, blinded clinical study. ANIMALS: Forty healthy dogs. Mean ± SD body mass 37.6 ± 6.6 kg and age 1.9 ± 1.3 years.
METHODS: Dogs were allocated randomly to receive an IV combination of dexmedetomidine, 0.3 mg m(-2), combined with butorphanol, 6 mg m(-2), (group DEX) or medetomidine 0.3 mg m(-2), combined with butorphanol 6 mg m(-2), (group MED). IOP and pulse (PR) and respiratory (f(R) ) rates were measured prior to (baseline) and at 10 (T10), 20 (T20), 30 (T30) and 40 (T40) minutes after drug administration. Oxygen saturation of hemoglobin (SpO(2)) was monitored following sedation. Data were analyzed by anova followed by Dunnett's tests for multiple comparisons. Changes were considered significant when p < 0.05.
RESULTS: Following drug administration, PR and f(R) were decreased significantly at all time points but did not differ significantly between groups. Baseline IOP in mmHg was 14 ± 2 for DEX and 13 ± 2 for MED. With both treatments, at T10, IOP increased significantly (p < 0.001), reaching 20 ± 3 and 17 ± 2 for DEX and MED respectively. This value for DEX was significantly higher than for MED. There were no significant differences in IOP values between groups at any other time points. At T30 and T40, IOP in both groups was below baseline (DEX, 12 ± 2 and 11 ± 2: MED 12 ± 2 and 11 ± 2) and this was statistically significant, for DEX. CONCLUSIONS AND CLINICAL RELEVANCE: At the documented doses, both sedative combinations induced a transient increase and subsequent decrease of IOP relative to baseline, which must be taken into consideration when planning sedation of animals in which marked changes in IOP would be undesirable.