Purpose: Our great interest in this work was study the synergism between L-tryptophan and dipyrone or paracetamol as well as the interaction of kynurenic acid (L-tryptophan metabolite) and these analgesics agents utilizing a robust methodology. Methods: We performed the writhing test induced by acetic acid in mice to evaluate the antinociceptive effect of the treatments isolated and combined (p.o. and i.p.). Do...