Onpi-to, an herbal medicine composed of five crude drugs (Rhei Rhizoma, Glycyrrhizae Radix, Ginseng Radix, Zingiberis Rhizoma and Aconiti Tuber), was administered orally to rats. Onpi-to includes 1.240% of total potential rhein derived from sennoside A, sennoside B, rhein 8-O-glucopyranoside and rhein. Plasma, urinary and biliary levels of rhein were determined by an HPLC-UV method. The plasma levels displayed curves characterized by maximum peaks at 8.3؎5.2 min, 8.3؎5.2 min and 20.0؎21.9 min

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... llowing dosages of 125, 250 and 500 mg/kg with mean concentrations of 1302.5؎926.4, 2973.6؎684.3 and 3118.8؎1701.2 ng/ml, respectively, followed by a subsequent decline. Area under the concentration-time curve (AUC)(0-48 h) at doses of 125, 250 and 500 mg/kg were 752.3؎321.5, 2443.3؎554.4 and 4443.2؎2641.3 ng · h/ml, respectively. In female rats, rhein plasma levels showed curves which had a maximum peak at 45.0؎16.4 min after a dosage of 250 mg/kg with mean concentration of 3058.0؎1533.7 ng/ml, followed by a subsequent decline. AUC(0-48 h) was 5537.7؎1876.0 ng · h/ml. The cumulative urinary excretion of rhein and of conjugated rhein was 3.14؎1.56% and 38.21؎18.87% of dose, respectively, 48 h after dosing at 500 mg/kg of Onpi-to in male rats. The cumulative biliary excretion of rhein was 1.34؎0.44% of dose 48 h after dosing at 500 mg/kg of Onpi-to in male rats.