Influence of the Dose and Frequency of Administration of Tramadol on Analgesia, Hematological, Biochemical Parameters, and Oxidative Status of Cats Undergoing Ovariohysterectomy

•Low doses of tramadol provide satisfactory postoperative analgesia in cats.•Repeated administration does not impair hematological and biochemical parameters.•No benefit of administering tramadol at higher doses and frequency were found. This study aimed to evaluate the effects of the repeated administration of tramadol subcutaneously on postoperative analgesia, liver, kidneys, and oxidative status in the postoperative period of cats undergoing ovariohysterectomy. Thirty-seven cats were randomly assigned to 5 groups, according to the postoperative analgesic treatment: NaCl 0.9%, GC; tramadol at 2 mg/kg, T2B (q12h) and T2T (q8h); or 4 mg/kg, T4B (q12h) and T4T (q8h). Oxidative status was assessed at baseline, 12 hours and 24 hours after the final administration of tramadol by the activity of superoxide dismutase (SOD), catalase (CAT), myeloperoxidase (MPO), butyrylcholinesterase (BuChE), and lipoperoxidation (MDA). Total blood count, serum biochemistry and urinalysis were compared between baseline and 12 hours posttramadol. Postoperative pain was evaluated by applying the Glasgow Feline Composite Measure Pain Scale at baseline, 3 (T3), 6 (T6), 8 (T8), 12 (T12), 24 (T24) e 36 (T36) hours after extubation. No side effects were observed. Tramadol increased SOD activity while CAT varied among groups in all time points but not over time. MDA levels increased from baseline to 12 hours in all groups but T4T. MPO activity decreased from baseline to 24 hours in some groups, including GC. Creatinine and phosphatase alkaline decreased in T2T, T4B, and T4T at 12 hours. Higher pain scores were observed from T3 to T8, except for GC. Rescue analgesia was administered only at T3. No difference in pain scores was observed from T8 onwards. Based on the findings, it is suggested that tramadol at 2 mg/kg every 8 hours is recommended for postoperative analgesia of cats undergoing ovariohysterectomy.