OBJECTIVE：To study the effects of rat intestinal flora on the pharmacokinetic parameters of pyrazinamide and its active metabolite pyrazinoic acid. METHODS ：Totally 16 SD rats were randomly divided into trial group and control group ，with 8 rats in each group. Trial group was given mixed antibiotics （streptomycin sulfate+neomycin sulfate ）intragastrically to construct pseudoaseptic rat model. After modeling ，both groups were given pyrazinamide intragastrically （150 mg/kg）. Before and 0.167， 0.333，0.667，1，1.5，2，3，4，6，9 h after administration ，0.1 mL blood sample was collected from orbital venous plexus ，and 0.3 mL blood sample was collected from orbital venous plexus 12，24 h after administration. Using phenacetin as internal standard ， LC-MS/MS method was adopted to determine the plasma concentration of pyrazinamide and pyrazinoic acid. The determination was performed on Agilent ZORBAX SB-Aq column with mobile phase consisted of 0.2％ formic acid （containing 8 mmol/L ammonium acetate）-methanol（gradient elution ）at the flow rate of 1 mL/min. The column temperature was set at 30 ℃，and sample size was 10 μL. The ion source was ESI and the temperature of ion source was 500 ℃. The collision gas was nitrogen and the pressure was 10 psi. The temperature of mass transfer interface was 100 ℃. The mass spectrum monitoring mode was multi reaction monitoring ， and the collection mode was positive ion mode. The monitoring transition ion-pairs were m/z 124.0→79.0（pyrazinamide），m/z 125.1→79.1（pyrazinic acid ）and m/z 180.0→110.2（internal standard ）. The de-clustering potential and collision voltage were 55， 26 and 85 V，24，23 and 28 V，respectively. The pharmacokinetic parameters were calculated and compared by using DAS 2.1.1 software. RESULTS ：The linear ranges of pyrazinamide and pyrazinoic acid were 25-5 000 ng/mL（r＝0.997 6）and 100-12 500 ng/mL（r＝0.999 0）. The lower limits of quantification were 25 and 100 ng/mL，respectively. Intra-batch and inter-batch accuracy were 92.93％-100.50％，and RSDs of intra-batch and inter-batch precision and matrix effect tests were all lower than or equal to 8.42％（n＝6 or n＝3）. Compared with control group ，tmax of pyrazinamide in trial group was prolonged significantly （P＜0.01）； there was no statistical significance in other pharmacokinetic parameters between 2 groups（P＞0.05）. CONCLUSIONS ：The absorption of single dose pyrazinamide is delayed with the change of intestinal flora in rats.