Abstract: The pharmacokinetics of robenidine hydrochloride in the plasma of channel catfish (Ictalurus punctatus) at different water temperatures (18, 28 ℃) were investigated in this study.The concentration of robenidine hydrochloride in the plasma of channel catfish was determined by HPLC-MS. Pharmacokinetic parameters were calculated by using the 3p97 Practical Pharmacokinetic Program software. The concentration-time data of robenidine hydrochloride in plasma were fitted to a two-compartment model at both 18 ℃ and 28 ℃ water temperature. The kinetic equations were C_{18 ℃}=4.17e^-0.01t+2.48e^-0.008t-6.65e^-0.05t, C_{28 ℃}=7.69e^-0.02t+0.13e^-0.01t-7.82e^-0.27t, respectively. The major pharmacokinetic parameters at water temperature 18 ℃ and 28 ℃ were as follows: The time point of maximum plasma concentration (T_peak) was 42.36 and 10.03 h, respectively, peak plasma concentration (C_max) was 3.51 and 5.76 μg·mL^-1, respectively. Relatively apparent distributed volume V/F(c) was approached to 3.79 and 2.78 L·kg^-1, respectively. The distribution rate constant α was 0.248 and 0.222 h^-1, respectively. The elimination rate constant β was 0.006 and 0.007 h^-1, respectively. The absorption half-time [T_1/2(ka)] was 14.67 and 2.54 h, respectively. The elimination half-time [T_1/2(β)] was 85.52 and 58.63 h, respectively. First-order rate constant for drug distributions from central compartment to peripheral compartment (K₁₂) was 0.000 2 and 0.000 2 h^-1,respectively. First-order rate constant for drug distributions from peripheral compartment to central compartment (K₂₁) was 0.009 and 0.01 h^-1, respectively. The areas under the curve was 554.18 and 326.74 μg·mL^-1·h^-1, respectively. The results showed that the temperature could significantly affect the absorption, distribution and elimination of robenidine hydrochloride in the plasma of channel catfish. Under high water temperature, the peak time of robenidine hydrochloride was short, the peak concentration value was about twice of that at low water temperature, and the water temperature had a greater influence on the areas under the curve, but had little influence on the renal clearance rate. It also provided a theoretical basis for the rational use of robenidine hydrochloride in channel catfish farming during different seasons.

Key words: robenidine hydrochloride, channel catfish (Ictalurus punctatus), pharmakokinetic, water temperature