International Journal of Pharmaceutical Science and Research

Authors
Nazmul Hasan, Al Mamun, Hazrat Belal, Atikur Rahman, Hanif Ali, Naoshia Tasnin, Tabassum Ara, Al Refat Rabbi, Md. Asaduzzaman, Amirul Islam

Abstract
Objectives: Callistemon viminalis, a common ornamental small tree, is traditionally used in folk medicine to treat various diseased conditions. This study was carried out to explore in vitro antioxidant and antibacterial activity of crude extracts of C. viminalis leaf using different solvent systems. Methods: Maceration process was used for extraction with five different solvents and primarily qualitative and quantitative phytochemical analysis were carried out by standard methods. Antioxidant activity was explored by several in vitro assay models whereas disc diffusion method was used to evaluate antibacterial property. Results: Qualitative assay detected the presence of different important phytoconstituents. Ethanol extract showed the highest content of phenolics (88.83±2.71 mg gallic acid/ g dry weight), flavonoids (65.48±2.74 mg of catechin/ g dry weight) and proanthocyanidins (17.39±0.64 mg of catechin/ g dry weight) except flavonol. The lower IC₅₀ values of DPPH (32.80±1.71 µg/mL) and ABTS (46.20±1.33 µg/mL) assay were found by methanol extract than that of standards and other extracts. The highest superoxide and nitric oxide scavenging activity were found in ethanol (IC₅₀: 39.04±1.36 µg/mL) and chloroform extract (IC₅₀: 89.12±1.38 µg/mL), respectively. In disc diffusion assay, ethanol and petroleum ether extract showed highest activity against gram positive bacteria (inhibition zone: 22 mm against S. aureus) at 400 µg/ disc concentration, but the antibacterial activity of most extracts was relatively lower against gram negative bacteria. Conclusion: The results of this investigation revealed potent antioxidant and antibacterial activity, therefore C. viminalis may have a promising therapeutic potential.