ABSTRACT
The treatment of pain before it initiates may prevent the persistent pain-induced changes in the central nervous system that amplify pain long after the initial stimulus. The effects of pre- or postoperative intraperitoneal administration of morphine (2 to 8 mg/kg), dipyrone (40 and 80 mg/kg), diclofenac (2 to 8 mg/kg), ketoprofen (10 and 20 mg/kg), and tenoxicam (10 and 20 mg/kg) were studied in a rat model of post-incisional pain. Groups of 5 to 8 male Wistar rats (140-160 g) were used to test each drug dose. An incision was made on the plantar surface of a hind paw and the changes in the withdrawal threshold to mechanical stimulation were evaluated with Von Frey filaments at 1, 2, 6 and 24 h after the surgery. Tenoxicam was given 12 or 6 h preoperatively, whereas the remaining drugs were given 2 h or 30 min preoperatively. Postoperative drugs were all given 5 min after surgery. No drug abolished allodynia when injected before or after surgery, but thresholds were significantly higher than in control during up to 2 h following ketoprofen, 6 h following diclofenac, and 24 h following morphine, dipyrone or tenoxicam when drugs were injected postoperatively. Significant differences between pre- and postoperative treatments were obtained only with ketoprofen administered 30 min before surgery. Preoperative (2 h) intraplantar, but not intrathecal, ketoprofen reduced the post-incisional pain for up to 24 h after surgery. It is concluded that stimuli generated in the inflamed tissue, rather than changes in the central nervous system are relevant for the persistence of pain in the model of post-incisional pain