Background Acute toxicity (LD50) test provides an indication on the range of doses of a substance that could be toxic to the body systems. This study was aimed at determining the LD50 of different extracts of Bombax costatum stem bark and its effects on the histology of liver and kidneys in rats. Results Phytochemical screening of n-hexane, ethanol and chloroform extracts of B. costatum stem bark has revealed the presence of alkaloids, flavonoid, saponins, steroid, terpenes, anthraquinones and cardiac glycosides. No mortality was recorded after testing all the different extracts on rats. However, mild body weaknesses and pilo erection were observed in the first hour of extracts’ administration. No statistically significant differences was observed in most of the serum levels of kidney function biomarkers, although a significant decrease (p < 0.05) in bicarbonate and increase (p < 0.05) in urea, respectively, were observed in chloroform extract treated group when compared to control. Further, no marked differences (p > 0.05) were observed in hematological parameters as well as in the liver functions biomarkers in all the 3 extract exposed groups when compared to the control, except significant decrease (p < 0.05) of total bilirubin level in chloroform extract exposed rats. Finally, histological sections of the liver and kidneys showed no aberrations. Conclusions Since no mortality and serious clinical manifestation were recorded, it is suggestive that oral acute administration of n-hexane, chloroform and ethanol extracts of B. costatum is greater than 5000 mg/kg. Hence, the plant has high safety margin and can be used within the dose of 5000 mg/kg body weight.

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