Studies on pharmacokinetic and bioavailability of robenidine hydrochloride in rabbits

To investigate the pharmacokinetics and bioavailability after oral administration of the coccidiostat, robenidine hydrochloride in rabbits.

A total of 16 healthy New Zealand white rabbits were allotted to two groups and received single intravenous administration of robenidine hydrochloride at the dose of 2.00 mg·kg^-1 and single oral administration at the dose of 100.00 mg·kg^-1 respectively. Blood samples were collected and analyzed by high-performance liquid chromatography (HPLC) using UV. Pharmacokinetic parameters were estimated using the Winnonlin^TM software package and the curve of time and concentration was obtained using SPSS 16.0.

After i.v. injection, area under the concentration-time curve (AUC) was 1.72 μg·h·mL^-1, plasma clearance (CI) was 1.17 L·h^-1·kg^-1, the volume of distribution was 2.87 L·kg^-1 and the half-life of elimination (t_1/2) was 1.72 h. After oral administration, t_1/2 was 8.94 h and AUC was 6.33 μg·h·mL^-1. Statistical analysis showed that there were significant differences between pharmacokinetic parameters of intravenous and oral administration (P < 0.05), and the bioavailability following oral administration was low (7.36%).

The volume of distribution following robenidine hydrochloride was high, suggesting that the drug was widely distributed in rabbits and eliminated rapidly; Robenidine hydrochloride for oral administration was rarely absorbed into the blood or blood circulation, and the residues in vivo was low.