Antinociceptive and Anti-inflammatory Activity of the Bark Extract of Plumeria rubra on Laboratory Animals

Aims: To evaluate the analgesic and anti-inflammatory effects of ethanolic bark extract of Plumeria rubra on experimental animal models.

Study Design: Assessment of antinociceptive and anti-inflammatory activity.

Place and Duration of Study: Department of Pharmacy, North South University, Dhaka, Bangladesh, between January 2011 and June 2011.

Methodology: The analgesic activity was evaluated by hot plate, acetic acid induced writhing and formalin induced writhing method in Swiss Albino mice divided into 4 different groups (control, standard diclofenac sodium and extract at two different doses of 250 and 500 mg/kg BW). The extract was also investigated for the anti-inflammatory effect on Long Evans rats using carrageenan induced rat paw edema method. For anti-inflammatory study, 24 rats were divided into 4 different groups each receiving either distilled water, standard drug or the extract at the doses of 250 and 500 mg/kg BW.

Results: Phytochemical analysis of the extract revealed the presence of tannins, alkaloids, flavonoids and terpenoids. The extract elicited a highly significant (p<0.001) analgesic activity in a dose dependent manner on hot plate method, acetic acid induced writhing test and also on both the early and late phases of formalin test at the doses employed. In the hot plate method, the extract increased the reaction time of heat sensation to 60.81% and 66.52% at the doses of 250 and 500 mg/kg BW respectively while that of the standard drug was 57.40% at the 3rd hour of study. In acetic acid induced writhing test, the percent inhibition of writhing response by the extract was 62.87% and 70.66% at 250 and 500 mg/kg doses respectively (p<0.001) which were even better than the standard drug diclofenac sodium (50.30%). The extract also significantly inhibited the licking response at the dose of 500 mg/kg in both the early phase (55.11%, p<0.01) and the late phase (66.43%, p<0.01) of formalin test while the standard drug inhibited by 52.27% and 72.03%, respectively. The oral administration of the extract significantly (p<0.001) inhibited inflammatory response induced by carrageenan in a dose dependent fashion. The most prominent inhibition of 61.68% (250 mg/kg) and 73.65% (500 mg/kg) were observed at the 4th hour of study.

Conclusion: The central and peripheral analgesic as well as anti-inflammatory effect of the ethanolic bark extract of P. rubra may be due to the presence of various chemical constituents specially flavonoids, tannins, alkaloids or terpenoids. These experimental findings would further establish the scientific basis of the traditional uses of the plant in the management and/or control of pain as well as inflammatory conditions.