Antinociceptive properties of extracts of new species of plants of the genus Phyllanthus (Euphorbiaceae).

The hydroalcoholic extract (HE) of the four new species of Phyllanthus, given intraperitoneally, produced significant inhibition of acetic acid-induced abdominal constrictions, with mean ID(50) values of 0.3, 1.8, 7.4 and 26.5 mg/kg for Phyllanthus amarus, Phyllanthus orbiculatus, Phyllanthus fraternus and Phyllanthus stipulatus, respectively. In the formalin test, the four species of Phyllanthus, also produced graded inhibition against both phases of formalin-induced licking, being more active in relation of the late phase. The HE of the Phyllanthus species elicited significant inhibition of the capsaicin-induced neurogenic pain, with mean ID(50) values of 8.9, 6.7, >30 and approximately 30 mg/kg for P. amarus, P. fraternus, P. stipulatus and P. orbiculatus, respectively. Given orally all HE of the Phyllanthus species were less potent and efficacious than when given by intraperitoneally. Results of the present study extend previous data and indicate that all extracts of Phyllanthus plants so far studied exhibit pronounced antinociception when assessed in chemical models of nociception, namely acetic acid-induced writhing, and formalin and capsaicin-induced licking.