Postoperative administration of the analgesic tramadol, but not the selective cyclooxygenase-2 inhibitor parecoxib, abolishes postoperative hyperalgesia in a new model of postoperative pain in rats.
OBJECTIVE
Using a new animal model of postoperative pain we recently developed, we investigated whether the selective cyclooxygenase-2 (COX-2) inhibitor parecoxib sodium, and the analgesic tramadol hydrochloride, attenuated mechanical primary hyperalgesia induced by minor surgery on the rat tail.


METHODS
For surgery, rats were anesthetized with isoflurane, a 20-mm-long incision was made through the skin and fascia of their tails, and the wound was sutured. Immediately after surgery, rats were injected intraperitoneally with parecoxib sodium (10 or 20 mg x kg(-1)), tramadol hydrochloride (10 mg x kg(-1)), or sterile saline (0.1 ml x kg(-1)). Hyperalgesia was assessed by measuring rats' response latencies to a blunt noxious mechanical stimulus (4 N) applied to their tails. Nociceptive testing was performed before surgery and 90 min after surgery.


RESULTS
Hyperalgesia was present in all saline-injected animals within 90 min of surgery. This hyperalgesia was not attenuated by postoperative injection of parecoxib. However, administration of tramadol completely prevented the development of postoperative hyperalgesia.


CONCLUSIONS
We have shown that the hyperalgesia in our model of postoperative pain is responsive to treatment with the analgesic tramadol, but it is not responsive to the selective COX-2 inhibitor parecoxib at the doses we used.
Kamerman
Peter
P
Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa. peter.kamerman@wits.ac.za
Koller
Anthony
A
Loram
Lisa
L
D000701:Analgesics, Opioid / Q000627:therapeutic use*; D000818:Animals; D052246:Cyclooxygenase 2 Inhibitors / Q000627:therapeutic use*; D004195:Disease Models, Animal; D006930:Hyperalgesia / Q000188:drug therapy*; D007555:Isoxazoles / Q000627:therapeutic use*; D010149:Postoperative Pain / Q000188:drug therapy*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014147:Tramadol / Q000627:therapeutic use*
D000701:Analgesics, Opioid; D052246:Cyclooxygenase 2 Inhibitors; D007555:Isoxazoles; D014147:Tramadol; C409945:parecoxib