Antinociceptive effect induced by fentanyl and its interaction with MK-801in rats: potentiation of fentanyl analgesia with MK-801

The aim of this study was to determine the effect of a NMDA receptor antago nist, MK-801, in fentanyl induced analgesia in female Wistar rats. Nocicept ion was assessed by the tail-flick: response and each animal was tested thr ee times: 20, 40 and 60 min after drug infusion. Animals received an i.p. i njection of saline, or fentanyl, MK-801 or fentanyl plus MK-801, dissolved in saline. Antinociception was achieved with the higher dose of fentanyl (0 .05 mg/kg) and was apparent at all times tested (P < 0.05). MK-801 (0.05 or 1.0 mg/kg) alone had no antinociceptive effects. Treatment with a non-anal gesic dose of fentanyl (0.025 mg/kg) plus MK-801 (0.05 mg/kg) produced a si gnificant analgesic effect on tail-flick responses 20 min after drug infusi on. The co-treatment with fentanyl (0.025 mg/kg) + MK-801 (1.0 mg.kg) produ ced significant analgesic effects at all times tested. Co-treatment with MK -801 and an opioid agent can decrease the total dose of opioid used to obta in analgesia. Med Sci Res 26:839-840. (C) 1998 Lippincott Williams & Wilkin s.