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ETHNOPHARMACOLOGICAL RELEVANCE In traditional Chinese medicine, processed aconite root (lateral root of Aconitum carmichaelii Debx.) is used as the principle herb of the Si-Ni decoction (SND) formula due to its cardiotonic effect, while its cardiotoxicity and neurotoxicity caused by diester and monoester diterpenoid alkaloids are reduced by compatibility of dried ginger and honey-processed liquorice in SND. AIM OF THE STUDY To investigate the detoxification of processed aconite root by compatibility of SND from the perspective of intestinal absorption with metabolism in intestinal bacteria. MATERIALS AND METHODS Decoctions of processed aconite root (AD), processed aconite root and honey-processed liquorice (ALD), and SND with the same amount of each herb were prepared, then were incubated in human intestinal bacteria juice (IBJ) in vitro for different durations. Bidirectional transmembrane transports of these decoctions and their IBJ-incubated decoctions were conducted on Caco-2 monolayers. Correlation between efflux ratios changes of benzoylmesaconine, benzoylaconine, benzoylhypaconine (monoester-diterpenoid alkaloids, MDAs) and hypaconitine (diester-diterpenoid alkaloids) from processed aconite root, and metabolic trends of compounds from honey-processed liquorice and dried ginger were also performed. RESULTS The absorption of MDAs from processed aconite root was increased by combination with honey-processed liquorice in ALD, but they were decreased significantly by the addition of dried ginger in SND. Take benzoylhypaconine for example, the Papp, AP to BL soared from (3.13 ± 0.18) × 10-7 cm/s in AD to (23.32 ± 3.51) × 10-7 cm/s in ALD, while it dropped to (1.12 ± 0.17) × 10-7 cm/s in SND. When herb combined decoctions metabolised by intestinal bacteria for 12 h, the efflux ratio of benzoylhypaconine were both increased from 0.56 to 1.21 in ALD and from 1.10 to 2.61 in SND, which was correlative with the generation of davidigenin and glycyrrhetic acid (the metabolites of chalcones and pentacyclic triterpenoids from liquorice) in ALD and with the metabolism of [6]-gingerol (the major compound from dried ginger) in SND, respectively. CONCLUSIONS Compatibility of SND altered the intestinal absorption of toxic MDAs and hypaconitine from processed aconite root. In SND, dried ginger rather than honey-processed liquorice played the role of detoxification of these toxic compounds in the intestinal absorption. The intestinal detoxification of SND was significantly and strongly correlative with metabolism of dried ginger and honey-processed liquorice by intestinal bacteria, simultaneously.