Phytochemical Screening, Toxicity, Analgesic and Anti-Pyretic Studies of Aqueous Leaf Extract of Plectranthus barbatus [Andrews. Engl.] in Rats

Plectranthus barbatus is a popular tropical perennial plant with a wide variety of traditional medicinal uses in tropical Africa, Hindu, Ayurvedic and traditional medicines of Brazil and China. The whole plant and the leaves have many folkloric uses for diverse ailments including pain, heart disease, convulsions, coughs and colds, asthma, bronchitis and tonsillitis among others. This study investigated the phytochemical components, acute toxicity, analgesic and anti-pyretic activities of the aqueous leaf extract of Plectranthus barbatus locally known as Ekizeera in Uganda. The plant leaves were authenticated, collected and decoction was done according to local method. Phytochemical screening was conducted using methods outlined by Trease and Evans and Harborne to determine the components of the extract. Acute toxicity tests were conducted in rats using modified Lorke’s method to determine the safety of the plant material. Analgesic studies were carried out using both a mechanical method (thermally induced pain by tail-flick) and a chemical method (formalin induced pain) in rats by administering extracts orally at 100, 200 and 400 mg/kg of body weight. The method of Al-Ghamdi, modified for local laboratory setting by Adzu was adopted and used for anti-pyretic test. Decoction yielded 9.9% extract. Phytochemical screening confirmed presence of saponins, tannins, alkaloids, terpenoids and essential oils. Acute toxicity tests revealed no deaths in rats after oral treatment with up to 10,000 mg/kg of extract. Tail-flick test was non-significant (p > 0.05) while formalin-induced pain test demonstrated significant activity (p < 0.05) with ANOVA and student t-tests. Anti-pyretic activity was non-significant (p > 0.05) with student t-test. These results suggest that the aqueous leaf extract of Plectranthus barbatus contains specific phytochemicals, has a potent dose dependent analgesic activity, no anti-pyretic activity and can be regarded as a safe medicinal plant to use traditionally, which might further be developed for conventional medical practice.