Effects of Prednisolone on the Pharmacokinetics of Loratadine after Oral and Intravenous Administration of Loratadine in Rats

The present study aims to investigate the effects of prednisolone on the pharmacokinetics of orally and intravenously administered loratadine in rats. A single dose of loratadine was administered orally (4 mg/kg) and intravenously (1 mg/kg) in the presence or absence of prednisolone (0.2 or 0.8 mg/kg). Compared to the oral control group, prednisolone (0.2 mg/kg, p < 0.05; 0.8 mg/kg, p < 0.01) significantly increased the area under the plasma concentration-time curve of orally administered loratadine by 54.0-96.4%. After oral administration, the peak plasma concentration of loratadine was significantly (0.2 mg/kg, p < 0.05; 0.8 mg/kg, p < 0.01) increased by 20.9-65.3% in the presence of prednisolone. Consequently, the relative bioavailability of loratadine was increased by 1.54- to 1.96-fold. Compared to the intravenous control group, the presence of prednisolone significantly (0.8 mg/kg, p < 0.05) increased the area under the plasma concentration-time curve of loratadine. Prednisolone enhanced the oral bioavailability of loratadine in this study. The enhanced bioavailability of loratadine may be due to inhibition both cytochrome P450 3A4-mediated metabolism and the efflux pump P-glycoprotein (P-gp) in the intestine and/or liver by the presence of prednisolone.