Preoperative calming effect of melatonin and its influence on propofol dose for anesthesia induction in healthy dogs

Objective To investigate the preoperative calming effect of melatonin and its influence on propofol dose for anesthesia induction in dogs. Study design Prospective, randomized, blinded, placebo-controlled clinical study. Animals A total of 50 healthy, adult, client-owned dogs scheduled for elective surgery. Methods Dogs were equally divided into treatment group M, which received 5 mg kg(-1) melatonin, and placebo-control group P (sucrose), both administered orally 2 hours prior to induction of anesthesia. Dogs were subjectively characterized and further designated as skeptical (group S; n = 18) or trustful (group T; n = 32). Behavior, calming effect and vital parameters (pulse rate, respiratory rate, blood pressure, rectal temperature) were evaluated before and after treatment. Propofol dose [mg kg(-1) intravenously (IV)] to allow endotracheal intubation and anesthesia induction quality was documented. Data were analyzed using a general linear model and Mann-Whitney U tests. Results Dogs in group MS (n = 10) were calmer than those in group PS (n = 8) at 90 minutes after drug administration (p = 0.047). Group MT (n = 15) required less propofol (5.98 +/- 0.96 mg kg(-1)) than group PT (n = 17; 7.04 +/- 1.82 mg kg(-1) IV; p = 0.048) and group MS (9.48 +/- 3.22 mg kg(-1) IV; p = 0.007). Group PS required 7.69 +/- 2.71 mg kg(-1) IV. Skeptical dogs showed more reactions during induction (p = 0.013). Vital parameters were within physiological ranges before and after treatment. Conclusion and clinical relevance Results showed that melatonin may be used to reduce propofol dose for anesthesia induction in trustful dogs. Skeptical dogs benefitted from the calming properties. Potentially, melatonin could be used to minimize the level of excitement before general anesthesia and to reduce the required propofol dose for induction.