Effect of methadone and acepromazine premedication on tear production in dogs

Abstract

ObjectivesTo evaluate the combined effect of intramuscular acepromazine and methadone on tear production in dogs undergoing general anaesthesia for elective, non-ocular procedures.DesignProspective, non-randomised, pre-post treatment study.SettingPatients were recruited from a referral practice in the UK.MethodsThirty 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.ResultsUsing 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).ConclusionsAn 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.

Evaluation of Tear Production as Measured by Schirmer Test I in Dogs after Acepromazine and Acepromazine–Methadone Premedication

“…The association of a sedative drug with a full µ-opioid agonist resulted in a marked decrease in tear production, suggesting an additional effect in reducing the STT 1 readings, as previously observed by Volk et al [18], who tested the combination of the two drugs administered at the same time in the same syringe. The simultaneous inoculation of methadone may maintain the down regulation of tear production by acepromazine, due to its sedative effect that can persist until 4-6 h. Some authors reported that the synergism between acepromazine and methadone provides more profound sedation in dogs than either drug administered individually, with an early onset of action and a longer effect [14].…”

“…Many authors have reported that tear production in dogs is affected by tranquilizers, sedatives, opioids and general anesthetic drugs [ 2 , 3 , 4 , 8 , 16 ], although a variable effect on canine tear production was reported due to the inoculation of full μ-opioid receptor agonists, either alone or in association with sedatives or tranquilizers [ 2 , 16 , 17 , 18 ].…”

“…Some authors have reported moderate to marked reductions in tear production in dogs by a combination of phenothiazine agents and full µ-opioid receptor agonists [ 2 , 16 , 17 , 18 ].…”

“…In dogs, the premedication before elective general anesthesia with the intramuscular administration of methadone and acepromazine induced a decrease in tear production [ 18 ]. Additionally, we have shown that dexmedetomidine reduces canine tear production up to 4 h of more after sedation, making it mandatory to use artificial moisturizing lubricant eye drops to reduce corneal discomfort [ 5 ].…”

Dexmedetomidine and Tear Production: Evaluation in Dogs as Spontaneous Model for Ocular Surface Disorders

“…The main cause is the suppression of parasympathetic innervation of the lacrimal gland, as demonstrated in rats and rabbits experimentally para-sympathectomized by sectioning of the greater superficial petrosal nerve [ 9 , 10 , 11 ]. A marked decrease in tear production after induction of anesthesia has been reported in humans [ 12 , 13 , 14 , 15 ] and in dogs, using different anesthetic and sedative protocols [ 16 , 17 , 18 , 19 , 20 , 21 ]. The loss of corneal integrity resulting from perioperative dry eye can lead to corneal abrasions, which are the most common ocular complication in humans during general anesthesia for non-ophthalmic surgery [ 20 , 22 ].…”