The ESa also did not appear to act similarly to opiods, another class of commonly used analgesic drugs, because opioids effectively block the first phase of formalin induced nociceptive behavior in mice and physiological heat-induced nociception. Although dipyrone and acetaminophen are two NSAIDs that are known to have weak anti-inflammatory action they exert antipyretic effects at INCB18424 similar or lower doses than those required for their analgesic effects. Therefore, these data suggest that the ESa contain compounds that mainly have antinociceptive effects that act specifically on nociceptor sensitization. After fractioning, two of these ESa-derived fractions showed a similar antinociceptive activity: the PE fraction and EA fraction. From the PE fraction two anthraquinones, 2-methylanthraquinone and 7-methoxy-2-methylanthraquinone, were isolated. Anthraquinones are potential antinociceptive drugs. For example, the anthraquinones diacerhein and emodin possess antinociceptive HhAntag691 activity in different models. Nevertheless, both anthraquinones that were isolated from the PE fraction failed to change formalin-induced nociception at the doses tested. Higher doses were not tested but these anthraquinones are unlikely responsible for the antinociceptive activity of the ESa because the doses used were the same as the PE fraction. Sitosterol, a compound found in the PE fraction, possesses antinociceptive activity at doses that are 10 times higher than the one used in the present study, suggesting that it is not responsible for the activity of this fraction. Therefore, compounds other than those isolated in the present study may be responsible for the antinociceptive activity of the PE fraction. This will be an issue for future studies. Conversely, a new hydronaphthoquinone derivative identified in the EA fraction, named AgD, very effectively reduced both carrageenan-induced mechanical hyperalgesia and the formalin- induced nociception. These data suggest that the antinociceptive activity of the ESa is at least partially related to the presence of AgD. Notably, the doses of the ESa and AgD that completely abolished carrageenan-induced hyperalgesia only partially reduced the nociceptive behavior induced by formalin. This may be attributable to the fact that formalin evokes very complex behavior that involves the sensitization and/or activation of nociceptors, and AgD specifically reduces nociceptor sensitization. Additionally, the ESa and AgD failed to produce antinociceptive effects when a thermal stimulus was used thus substantiating their preferential peripheral action in nociceptive responses of inflammatory origin.