Background: Aminophylline is widely used for the treatment of asthma, but the therapeutic dose is very close to the toxic dose, which makes this drug prone to accumulation poisoning. In the present study, we explored whether the Chinese herbal component, Praeruptorin E (PE), enhances anti-asthma efficacy and prevents the toxicity of aminophylline.Methods: First, an ovalbumin (OVA)-induced mouse model of asthma, immunohistochemistry, pathological staining, and bronchoalveolar lavage fluid (BALF) were used to detect the lung condition of asthmatic mice. The content of Th2 cytokines in serum was measured by enzyme-linked immunosorbent assay (ELISA), and the expression of related proteins was detected by Western blotting and immunofluorescence.Concentrations of theophylline and its metabolites in rat serum were analyzed by liquid chromatographytandem mass spectrometry (LC-MS/MS). siRNA transfection and chromatin immunoprecipitation (ChIP) were used to investigate the mechanism of PE.Results: PE was found to synergize with aminophylline to reduce the infiltration of inflammatory cells, collagen deposition, and mucus hyperplasia in the lungs of asthmatic mice. It inhibited the expression of Th2 cytokines, interleukin (IL)-4, IL-5, and IL-13; promoted lung tissue repair; and reduced the toxic effect of aminophylline on the heart. Moreover, LC-MS/MS analysis showed that PE reduced the plasma concentration of the parent theophylline and its metabolite 1,3-dimethyluric acid (1,3-DMU). PE facilitated aminophylline's suppression of nuclear factor-κB (NF-κB), and increased the expression of the xenobiotic nuclear receptor pregnane X receptor (PXR) and its primary target gene, CYP3A11