Observer-blinded comparison of two nonopioid analgesics for postoperative pain in piglets

Piglets are popular for studies of respiratory and cardiovascular function, but opioid analgesics are contraindicated in these studies because of central nervous system depression. We evaluated two nonopioid analgesics for postoperative pain relief following implantation of a central arterial catheter via an inguinal incision. Animals were randomly assigned to paracetamol-treated (n=8, rectal suppositories, 100 mg/kg) meloxicam-treated (n=8, 1 mg/kg meloxicam via the catheter) or untreated control group (n=8, placebo suppositories and normal saline). Additional controls received paracetamol or meloxicam, without pain (n=6 for both groups). Behavioral and physiological assessments, and blood sampling were undertaken at nine timed intervals until 24 h after surgery. Multifactorial numerical rating scale (NRS), behavioral and physiological pain scores (PPS) decreased over time for all groups (P<.001). On NRS and behavioral criteria, meloxicam was significantly better than paracetamol (P<.001), and both were better than control (p<.001 for each). Physiological parameters discriminated between the control and analgesia-treated groups, but not between paracetamol and meloxicam. Preliminary pharmacokinetics, determined by isocratic high-performance liquid chromatography (HPLC), revealed no difference in the half-life of paracetamol (2.5+/-0.3 h) vs. meloxicam (3.4+/-0.4 h). Paracetamol and meloxicam provided effective postoperative analgesia in piglets, with meloxicam superior to paracetamol on behavioral criteria.