E. coli infection modulates the pharmacokinetics of oral enrofloxacin by targeting P-glycoprotein in small intestine and CYP450 3A in liver and kidney of broilers.

P-glycoprotein (P-gp) expression determines the absorption, distribution, metabolism and excretion of many drugs in the body. Also, up-regulation of P-gp acts as a defense mechanism against acute inflammation. This study examined expression levels of abcb1 mRNA and localization of P-gp protein in the liver, kidney, duodenum, jejunum and ileum in healthy and E. coli infected broilers by real time RT-PCR and immunohistochemistry. Meanwhile, pharmacokinetics of orally administered enrofloxacin was also investigated in healthy and infected broilers by HPLC. The results indicated that E. coli infection up-regulated expression of abcb1 mRNA levels significantly in the kidney, jejunum and ileum (P<0.05), but not significantly in the liver and duodenum (P>0.05). However, the expression level of CYP 3A37 mRNA were observed significantly decreased only in liver and kidney of E. coli infected broilers (P<0.05) compared with healthy birds. Furthermore, the infection reduced absorption of orally administered enrofloxacin, significantly decreased Cmax (0.34 vs 0.98 µg mL(-1), P = 0.000) and AUC0-12h (4.37 vs 8.88 µg mL(-1) h, P = 0.042) of enrofloxacin, but increased Tmax (8.32 vs 3.28 h, P = 0.040), T1/2a(2.66 vs 1.64 h(-1), P = 0.050) and V/F (26.7 vs 5.2 L, P = 0.040). Treatment with verapamil, an inhibitor of P-gp, significantly improved the absorption of enrofloxacin in both healthy and infected broilers. The results suggest that the E. coli infection induces intestine P-gp expression, altering the absorption of orally administered enrofloxacin in broilers.

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