Possible involvement of noradrenergic descending pain-modulating pathways in the mode of antinociceptive action of flupirtine, a novel non-opioid analgesic.

These experimental studies were conducted to obtain information about the antinociceptive action of flupirtine within the central nervous system. Flupirtine dose-dependently increased pain threshold in the electrostimulated pain test in mice. Its antinociceptive activity was attenuated by simultaneous administration of the noradrenergic alpha 1/alpha 2-antagonist yohimbine and alpha 2-antagonist idazoxane. By contrast, the analgesia induced by codeine or morphine was not influenced by alpha 2-adrenergic antagonists at all. A striking resemblance could be observed in the pharmaco-EEG of freely moving rats treated with clonidine and flupirtine, respectively. The present results are consistent with the hypothesis that the noradrenergic descending pain-modulating system might be involved in the antinociceptive mode of action of flupirtine.