OBJECTIVE： To establish the method for determining the concentration of leukotriene B4 （LTB4） in plasma of airway inflammatory guinea pigs， investigate the effects after giving Belamcanda chinensis extract on plasma concentration of LTB4 in guinea pigs and provide reference for clarifying the mechanism of anti-inflammatory and antitussive effects of B. chinensis extract. METHODS： Totally 30 guinea pigs were randomly divided into blank group， model group and B. chinensis extract group， with 10 guinea pigs in each group. Except for blank group， airway inflammation model was induced by smokation+syncytial virus intranasal method in other 2 groups. At next day after modeling， guinea pigs were given relevant medicine （10 mg/kg B. chinensis extract， calculated by irigenin） intragastrically in B. chinensis extract group； blank group and model group were given constant volume of normal saline intragastrically， once a day， for consecutive 7 d， and the plasma samples were collected after last administration. Then， the effects of surface active agent Triton X-114 concentration， hydrochloric acid concentration， hydrochloric acid amount. Equilibrium temperature and equilibrium time on extraction recovery rate of LTB4 were investigated （using 44.5        g/mL BAS saline solution instead of blank plasma）. The optimal cloud point extraction technology was determined for biological sample treatment. Using indometacin as internal standard， UPLC- MS/MS method was used to determine the concentration of LTB4 in plasma. Chromatographic conditions： the chromatographic column is ACQUITY UPLC BEH C18， the mobile phase is 0.2％ formic acid-acetonitrile （40 ∶ 60，V/V）， flow rate is 0.4 mL/min， column temperature is 40 ℃， sample volume is 5 μL. MS condition： Electrospray ion source

positive ion mode scanning

and the LTB4 used for the [M+H]+ mass ratio (m/z) 335.219 4→195.099 8， Indomethacin is [M+H]+ m/z 356.083 6→312.084 2. RESULTS： The optimal cloud point extraction condition included Triton X-114 concentration 5％， added into 0.3 mol/L hydrochloric acid 50 μL adjusted to acid and equilibrium temperature 50 ℃， for 20 min. The results of methodology validation were all in line with the content determination requirements. Compared with blank group， the plasma concentration of LTB4 in guinea pigs was increased significantly in model group （P＜0.05）. Compared with model group， the plasma concentration of LTB4 in guinea pigs was decreased significantly in B. chinensis extract group （P＜0.05）. CONCLUSIONS： The method of sample processing is environmental friendly， and the content determination method is high sensitivity and accuracy， and applicable for determination of LTB4 in plasma samples. B. chinensis extract can significantly regulate the increase of LTB4 concentration in plasma of guinea pigs with airway inflammation.