Antinociceptive effects of metamizol (dipyrone) in rat single motor units.

Metamizol has been considered as a peripherally acting non-steroidal antiinflammatory drug, though a central action is possible. The aim of the present study was to elucidate if metamizol induces antinociception in the single motor unit preparation, in normal rats versus rats with carrageenan-induced monoarthritis, and whether this action is produced at central and/or peripheral sites. Metamizol induced a potent antinociceptive effect in both groups of animals, though the effect on responses evoked by natural stimulation was stronger in hyperalgesic rats. Metamizol also depressed wind-up in a dose-dependent manner. We conclude that metamizol is a potent antinociceptive agent both in normal and hyperalgesic animals and that the effect was induced both at peripheral and central sites, at the level of the spinal cord.