Acute Toxicity Evaluation of Aqueous Extract of Azadirachta indica Bark in Wistar Rats

Azadirachta indica, commonly known as neem, is extensively used in traditional Nigerian veterinary medicine to treat a range of conditions including ectoparasitic infestations, wound infections, and gastrointestinal disorders. Despite widespread use, the safety profile of bark extracts administered systemically remains inadequately characterised in laboratory models. This study evaluated the acute oral toxicity of aqueous extract of Azadirachta indica bark in Wistar rats according to the Organisation for Economic Cooperation and Development Guideline 425. Thirty rats were randomly assigned to five groups receiving 0, 250, 500, 1000, and 2000 mg/kg body weight of the extract by gavage. Animals were observed for clinical signs of toxicity at 0.5, 1, 2, 4, 6, 12, and 24 hours post-administration and daily for 14 days. Body weights were recorded on days 0, 7, and 14. At termination, blood samples were collected for haematological and biochemical analysis, and major organs were harvested for histopathological examination. No mortality was observed at any dose level. Animals at the 2000 mg/kg dose exhibited transient signs of sedation, reduced motor activity, and mild diarrhoea within the first six hours. Serum liver enzymes were mildly elevated at this dose, but histopathological examination revealed no significant hepatic lesions. The median lethal dose was estimated to exceed 2000 mg/kg. These findings suggest that the aqueous bark extract has a wide safety margin at doses used in traditional practice. Keywords: Azadirachta indica, acute toxicity, Wistar rats, neem, LD50.