The Pharmacokinetic Study of Tanreqing Injections in Pneumonia Model Rats and the Effect of Cefixime on Tanreqing Injections During Combined Administration by UPLC–MS/MS

Combining traditional Chinese medicine and chemical drugs with antimicrobial activities has become more popular, but there is insufficient relevant research on such combinations. The Tanreqing injection ( TRQI ), a Chinese compound medicine, exhibits therapeutic effects in treating upper respiratory tract infections, severe influenza, and pneumonia. This research investigates the pharmacokinetics of TRQI in pneumonia model rats and explores the effect of the antibiotic cefixime on its metabolism. The pneumonia model rats were randomly divided into four groups: low, medium, and high (3, 6, and 12 mL·kg −1 ) dose TRQI group, and a medium dose TRQI combined with cefixime (48 mL·kg −1 ) group. Blood samples were collected from the tail vein at different time points between 0–24 h after injection. A sensitive and quick method based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC–MS/MS) was established for the simultaneous determination of the 13 TRQI components in the blood samples. The analytes were separated on an XBridge TM C 18 column (2.1 mm × 150 mm, 5 um), with the flow phase consisting of methanol and 0.1% formic acid water at a flow rate of 0.3 mL/min. The assay method met the biological sample determination requirements, demonstrating good adaptability and practicability for application in the pharmacokinetic study of TRQI in pneumonia model rats. Moreover, the method was used successfully in the interaction study of TRQI with cefixime. The results indicated that co-administration results in a significant change in the pharmacokinetic parameters of the main TRQI components. However, the changes in the pharmacokinetic characteristics of multiple TRQI components were inconsistent. Thus, the results of this drug combination under different pathological conditions in clinical applications were unpredictable. Therefore, more attention should be paid to the combined use of cefixime and TRQI in clinical applications to avoid the risk of adverse drug reactions in future studies.