Antinociceptive effects of (+/-)-, (+)- and (-)-nefopam in mice

The antinociceptive activity of (+/-)-, (+)- and (-)-nefopam in mice has been examined using the hot-plate, formalin and tail-flick tests. Nefopam was administered by the intraperitoneal, intracerebroventricular (i.c.v.) and intrathecal (i.th.) routes. Intraperitoneal injection of (+/-)-nefopam (10-20 mg kg-1) had powerful analgesic effects in the hot-plate and formalin tests. In the tail-flick test it produced a weak, but significant elevation of the response latencies. In spinalized animals, however, the effect was abolished, indicating that nefopam prolonged the tail-flick latencies by activation of descending pain-modulating pathways. (+/-)-Nefopam (5-20 micrograms) elicited analgesia in the hot-plate test after i.c.v. or i.th. injection. These findings suggest that nefopam has both a spinal and a supraspinal site of action. (+)-Nefopam was significantly more potent than (-)-nefopam after both systemic and central administration.