Analgesic and anti-inflammatory activities of ethanolic extract of the leaf of Verbena hastata in albino mice and rats

Background: Verbena hastate is a medicinal herb used in Africa to treat ailments such as convulsion, swellings, pain and emesis. In this study, the analgesic and anti-inflammatory activities of the crude ethanol extract of Verbena hastate (CEEVH) was evaluated using theacetic acid-induced writhing, Tail immersion tests and carrageenan-induced paw edema in mice.Methods: Acetic acid-induced writhing and tail immersion were used to determine the antinociceptive efficacy, whereas carrageenan-induced paw oedema was employed for the anti-inflammatory study. In each of the assays, groups 2, 3, 4, and 5 received 17.5, 35 and 70mg/kg of extract and aspirin (150 mg/kg) or Indomethacin (10 mg/kg) correspondingly while group 1 was administered 10 ml/kg normal saline. Extract, normal saline, and morphin (5mg/kg) or aspirin (150 mg/kg) or Indomethacin (5 mg/kg) were administered orally 1 hourbefore the induction of pain or inflammation. The sub-chronic toxicity study was investigated in rats administered with 70 mg/kg doses of the extract orally for 28 days using standard laboratory procedures after the acute toxicity was carried out. Phytochemical and acutetoxicity studies were determined by standard methods.Results: The extract (17.5-70 mg/kg, i.p.) produced significant (P<.05) dose-dependent inhibition of pain response elicited by acetic acid with percentage inhibition of 37.96, 49.38, and 78.37% and also increased the nociceptive reaction latency in the tail immersion test.Similarly, the CEEVH elicited significant (P<.05) dose-dependent inhibition of oedema paw size by 15, 32, and 47% respectively. The effects of the extract in these experimental models were comparable with the impact of the standard drugs used. Phytochemical screening of the extract revealed the presence of tannins, saponins, phlobatannins, and anthraquinones. The median lethal dose (LD50) of the extract was calculated to be 177.5 mg/kg body weight in rats orally administered. The study revealed that crude ethanol extract of Verbena hastata contains components that have anti-nociceptive and anti-inflammatory properties. Histopathological studies on the liver showed moderate hepatocellular necrosis at doses of 35 and 70 mg/kg. The Kidney showed intense necrosis of tubules and glomerular necrosis with lymphocyte hyperplasia at all doses tested.Conclusion: Verbena hastate extract showed analgesic and anti-inflammatory effects in rodents at the doses investigated. The extract possesses both central and peripheral analgesic activities. The study indicates that prolonged use of the extract in the management of disease conditions may be associated with adverse effects on some vital organs.