An evaluation on antinociceptive effects of eugenol by formalin test in rats

Statement of Problem: Eugenol is the most important chemical compound of the clove tree (Eugenia aryophylata) extract. That is widely used in dentistry as a bactericidal and pain relieving agent. The aim of the current study was to evaluate the antinociceptive effect of local and systemic administration of eugenol by formalin test in rats. In this research, 56 male Wistar rats, weighing 230±20 g were divided into seven groups (n=8). Ten minutes before formalin test, different doses of eugenol (12.5,25,50 mg /in groups 2,3,4 respectively) were injected to the right hind paw of the rats subcutaneously. In- group 5 eugnol (50 mg) was. injected to the contralateral hind paw. In group 6 eugenol (100 mg/ kg) and control group (group 7), equal volume of norma! saline was injected intraperitonealy. The minutes 0-5 and 16-60 were considered as acute and chronic phases of pain in the formalin test, respectively. Data were statistically analyzed by ANOVA and Tukey's tests. The results showed that local injection of eugenol to the same paw receiving formalin caused a decrease of nociception in both acute and chronic phases of formalin test (PO.005). However, in the group that eugenol (50mg/ kg) was injected to the contralateral paw, no significant differences were observed in the pain score in comparison with the control group. Intraperitoneal injection of eugenol (lOOmg/kg) did not reduce the nociception in the acute phase, but it caused a significant decrease of nociception in tonic phase (PO.00I). It was concluded that eugenol, as a local anesthetic drug not only inhibits nociceptive impulse conduction on the peripheral pain fibers, but also centrally reduce chronic pain.