Pharmacokinetics of Baicalin Following Single Oral Administration in Tilapia ( <i>Oreochromis niloticus</i> )

Baicalin, a bioactive flavonoid from Scutellaria baicalensis, shows significant therapeutic efficacy on tilapia (Oreochromis niloticus) bacterial infections, but its application remains limited due to the lack of pharmacokinetic data. In this study, single oral administration of baicalin at 12 mg/kg was carried out in O. niloticus under 32°C. Then, samples of plasma, kidney, bile, muscle, liver and brain were collected at various time intervals up to 96 h. A high-performance liquid chromatography (HPLC) method was developed and validated for baicalin quantification assay in each sample and subjected to non-compartmental analysis. Results showed that baicalin was rapidly absorbed following oral administration. A double-peak phenomenon was observed in tilapia plasma. The first (C_max1) and the second (C_max2) peaks were 46.828 μg/mL at 1 h and 17.069 μg/mL at 4 h, respectively. The elimination half-life (t_1/2) and the volume of distribution (V_d) were 26.654 h and 0.462 L/kg, respectively. A double-peak phenomenon was also observed in kidney and liver. The C_max1 and C_max2 in kidney were 66.981 μg/g at 2 h and 85.577 μg/g at 8 h, respectively, and in liver were 34.147 μg/g at 2 h and 39.971 μg/g at 8 h. While a single peak was observed in brain and bile, their C_maxs were 29.787 μg/g at 8 h and 63.038 μg/g at 12 h, respectively. Notably, the triple-peak phenomenon was observed in muscle and the C_max1, C_max2 and C_max3 were 55.771 μg/g at 1 h, 23.603 μg/g at 4 h, 25.488 μg/g at 12 h and 30.192 μg/g at 48 h. The t_1/2 of baicalin in kidney, liver, brain and bile were 57.273, 38.169, 38.169, 8.315 and 72.705 h, respectively. In plasma, liver, kidney, brain, muscle and bile, the area under the concentration-time curve from 0 to 96 h relative to the half maximal inhibitory concentration against Streptococcus agalactiae β-hemolysin/cytolysin (AUC_{0-96 h}/IC₅₀) of baicalin were 132.755, 443.169, 731.920, 66.283, 452.864 and 540.540 h, respectively; the peak concentration to IC₅₀ ratio (C_max/IC₅₀) in plasma, liver, kidney, brain, muscle and bile were 8.688, 7.416, 15.877, 5.526, 10.347 and 11.695, respectively; the concentration remained above the IC₅₀ (T > IC₅₀)for over 96 h in all tissues examined, with the exception of the brain (27.205 h). These results provide a scientific basis for the application of baicalin in the prevention and control of tilapia bacterial diseases, especially tilapia streptococcosis.