Pharmacokinetics and Acute Safety Evaluation of Tryptanthrin, A Bioactive Constituent of Indigo naturalis, Following Intravenous Administration in Mice

ABSTRACT The use of Indigo naturalis in treating inflammatory diseases is clinically restricted by severe adverse events, including pulmonary arterial hypertension and hepatotoxicity. Tryptanthrin, a major indoloquinazoline alkaloid of Indigo naturalis , exhibits potent anti‐inflammatory activity; however, its specific safety profile relative to the crude extract remains unclear. This study aimed to elucidate the intravenous pharmacokinetics and acute safety of purified tryptanthrin to validate its potential as a safer pharmacological alternative. Following a single intravenous injection of 30 mg/kg—a dose range relevant to its pharmacological efficacy—in ICR mice, plasma concentrations were quantified using a validated LC–MS/MS method. Tryptanthrin exhibited rapid systemic distribution and biphasic elimination, characterized by a large volume of distribution (V ss 23.1 L/kg) and rapid clearance (6.54 L/h/kg), indicating extensive tissue penetration and efficient systemic elimination. Importantly, over a 14‐day observation period, no mortality, behavioral abnormalities, or significant alterations in hepatic (AST, ALT, total bilirubin) and renal (BUN, creatinine) biochemical parameters were observed. These findings indicate that purified tryptanthrin does not induce the acute hepatic or renal toxicity frequently associated with crude Indigo naturalis preparations. This study provides the first pharmacokinetic characterization and safety validation of tryptanthrin at a therapeutic dose, supporting its preclinical development as a safe, single‐chemical entity for systemic administration.