Sedative, physical and behavioral effect produced by a subdose of methadone on the Yin Tang acupoint of cats

Abstract

Acupuncture is an ancient Chinese technique in which acupoints are stimulated by needles. The stimulation of acupoints by drugs is called pharmacopuncture and the use of subdoses reduces side effects. Methadone is a synthetic opioid capable of providing good analgesia and mild sedation. The objective of this study was to verify the sedative, physical and behavioral effect produced by a subdose of methadone administered to the Yin Tang acupoint of cats. This was a prospective, randomized, double-blind study. 36 healthy cats, 21.8 ± 13.4 months old and weighing 3.6 ± 0.9 kg, were used. After 60 minutes of adaptation to the environment, at T0 (time zero) the cats underwent baseline assessment of heart rate (HR), respiratory rate (RR), non-invasive systolic blood pressure, rectal temperature, pupil diameter, presence of sialorrhea, nausea, vomiting, excitement, vocalization, 3rd eyelid exposure and sedation score. Treatments were then carried out according to the experimental group, being G1 (n = 7): 0.05 ml of 0.9% NaCl at the Yin Tang acupoint and 0.05 ml of 0.9% NaCl SC; G2 (n = 7): 0.05 ml of 0.9% NaCl at the Yin Tang acupoint and 0.05 mg/kg of methadone SC; G3 (n = 7): 0.05 ml of 0.9% NaCl at the Yin Tang acupoint and 0.10 mg/kg of methadone SC; G4 (n = 8): 0.05 mg/kg of methadone at the Yin Tang acupoint and 0.05 ml of 0.9% NaCl SC; and G5 (n = 7): 0.10 mg/kg of methadone at the Yin Tang acupoint and 0.05 ml of 0.9% NaCl SC. There was a reassessment of the parameters at T10min, T20min, T30min, T40min, T50min and T60min. Parametric data were submitted to one-way ANOVA followed by Tukey, while non-parametric data were submitted to Kruskal Wallis, always with p < 0.05. There was no significant variation in HR, systolic blood pressure, 3rd eyelid exposure and sialorrhea score, nausea, vomiting, excitement and vocalization. There was subtle and transient variation in RR, rectal temperature and pupil diameter. Regarding sedation, it was observed that between times the G4 score at T0 was lower than at T40; and in G5 the score for T20, T30 and T40 was higher than that seen in T0, T10, T50 and T60. Between groups, at T0, T10, T50 and T60 there was no significant variation, however, at T20, T30 and T40, the score of G4 and G5 was higher than that presented by G1, G2 and G3. These findings showed that subdoses of methadone in Yin Tang practically did not interfere with physical and behavioral parameters, but were capable of promoting mild sedation. Thus, it is concluded that subdoses of methadone (0.05 or 0.10 mg/kg) applied to the Yin Tang of cats promote mild sedation free of side effects. The protocol with 0.10 mg/kg is more effective.