Pharmacokinetics and oral bioavailability of amoxicillin in chicken infected with caecal coccidiosis

Chicken infected with caecal coccidiosis (Eimeria tenella) was used to evaluate the effect of coccidiosis on the pharmacokinetic and bioavailability of amoxicillin. The level of amoxicillin was estimated by high‐performance chromatography (HPLC) to calculate the pharmacokinetic parameters and oral bioavailability. For i.v. injection of amoxicillin, Vd and CL were 0.29 and 0.27 (mg/kg)/(μg/mL)/h, respectively. Compared with healthy chicken, intravenous injection of amoxicillin in the infected chicken showed higher distribution and elimination constants, delayed clearance and statistically significant higher AUC and MRT. Oral administration in healthy chicken was accompanied by rapid absorption and high bioavailability with T_max, C_max and F about 1.03 h, 3.26 μg/mL and 40.2, respectively. Furthermore, oral administration in the infected chicken produced higher mean absorption time, delayed T_max, lower C_max, smaller AUC value and lower bioavailability (16.76). Based on these results, monitoring and adjustment of amoxicillin dosing could be practiced during the presence of coccidiosis. The measured C_max values suggest the administration of 1.3‐folds of the normal dose to maintain the normal maximal serum concentrations of amoxicillin in chicken infected with caecal coccidiosis.