Objectives To evaluate the combined effect of intramuscular acepromazine and methadone on tear production in dogs undergoing general anaesthesia for elective, non-ocular procedures.
Design Prospective, non-randomised, pre-post treatment study.
Setting Patients were recruited from a referral practice in the UK.
Methods Thirty client-owned dogs were enrolled in this study and received a combined intramuscular premedication of methadone (0.3 mg/kg) and acepromazine (0.02 mg/kg) before general anaesthesia for elective, non-ocular procedures. Full ophthalmic examination was performed and tear production was quantified using the Schirmer tear test-1 (STT-1). On the day of general anaesthesia, an STT-1 was performed before (STT-1a) and after (STT-1b) intramuscular premedication with methadone/acepromazine.
Results Using a general linear model, a significant effect on STT-1 results was found for premedication with methadone/acepromazine (P=0.013), but not eye laterality (P=0.527). Following premedication, there was a significant reduction observed in the mean STT-1 readings of left and right eyes between STT-1a (20.4±2.8 mm/min) and STT-1b (16.9±4.1 mm/min; P<0.001). Significantly more dogs had an STT-1 reading less than 15 mm/min in one or both eyes after premedication (30 per cent; 9/30 dogs) compared with before premedication (6.7 per cent; 2/30 dogs; P=0.042).
Conclusions An intramuscular premedication of methadone and acepromazine results in a decrease in tear production in dogs before elective general anaesthesia. This may contribute to the risk of ocular morbidities, such as corneal ulceration, particularly in patients with lower baseline tear production.
- schirmer tear test
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Contributors HAV, RLP, AP and DJG were involved in the study design. HAV was primarily involved with the acquisition of data and recruitment of subjects. EW was responsible for the statistical analysis and interpretation of data for the work. RLP, GVF and DJG were responsible for ophthalmic examination of subjects. All authors gave final approval of the version to be published.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Ethics approval This study received institutional ethical approval from The Animal Health Trust Clinical Research Ethics Committee, Newmarket, UK (project number 23_2013, approved 24 September 2013).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement There are no additional unpublished data.
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