Analgesic and clinical side effects of paracetamol and meloxicam in female dogs after elective ovariectomy or ovariohysterectomy – randomized clinical trial

Abstract Background This prospective, randomized, blinded, controlled clinical trial aimed at comparing the analgesic and antihyperalgesic effect of paracetamol and meloxicam following elective ovariectomy or ovariohysterectomy in healthy female dogs. In addition, it aimed at evaluating gastrointestinal side effects up to 48 h after surgery. Standardised anaesthesia protocol was utilised in all dogs and, at the end of the surgery, either meloxicam (0.2 mg/kg, Group M, n = 15 dogs) or paracetamol (10 mg/kg, Group P, n = 15 dogs) was administered intravenously. Pain was evaluated at 1, 2, 3, 4 and 6 h after the administration of either paracetamol or meloxicam using short form of Glasgow composite pain scale (GCPS-SF). Rescue analgesia with intravenous methadone (0.2 mg/kg) was administered in case of ≥ 6 over 24 points. The success rate of each treatment was calculated based on the need of rescue analgesia within 6 h after surgery. Subsequently, the success rate was assessed for non-inferiority between treatments. The non-inferiority margin was set as -33%. Mechanical nociceptive thresholds and sensitivity to Von Frey filaments were tested at 2, 4 and 6 h after the administration either paracetamol or meloxicam. Once discharged, animals were remotely evaluated through a standardized questionnaire. Results Rescue analgesia was administered at the hospital during the 6-hour post-operative period in a total of 15 dogs without difference between groups ( p = 0.358). The success rate for analgesia was (9/15) 60% and (6/15) 40% in group M and P, respectively. The lower limit of the 95% CI of the difference for success rate (-55%, 15.5%) was lower than the margin set for non-inferiority (-33%) and therefore the non-inferiority of the group P versus group M was not confirmed. Mechanical sensitivity increased in both group after surgery. Mild self-limiting gastrointestinal side effects were detected in both groups. Conclusions Dogs receiving paracetamol needed more rescue analgesia than dogs receiving meloxicam in the post-operative period. The rate of success with both drugs was lower than expected. Frequent assessment of pain is mandatory to ensure efficient analgesia also beyond the first post-operative day and future studies are warranted to validate methods for out-of-hospital pain assessment.