Bioavailability of coated amoxicillin in pigs field experiences

Amoxicillin, a -lactam antibiotic widely used in pigs, has a broad spectrum of action and bactericidal activity against the commo n respiratory pathogens. The aim of the present study was to identify the bioavailability and pharmacokinetic behaviour of two different formulations of amoxicillin orally administered to pigs. A new premix for medicated feedstuff containing 10% of coated amoxicillin, was developed using a hydrophobic matrix and was compared with a premix for medicated feedstuff containing 10% of not coated amoxicillin. Two feed formulations medicated with 20 gr. of the two premixes for medicated feedstuff were administered to 8 pigs using a two period, two sequence crossover design with a 7 days washout period. Medicated feed was administered to pigs as a single dose at 8 mg/kg b.w., and was rapidly and totally consumed. Amoxicillin analyses in serum were performed by a sensitive high performance liquid chromatography (HPLC) method with fluorometric detection, using an extraction procedure already described for edible tissues of fish and adapted and validated for pig serum. The oral bioavailability of the formulation with coated amoxicillin was higher than the one of not coated amoxicilli n and the area under the concentration-time curve (AUC) values was significantly different (P<0.05). Differences between the mean maximum concentration (Cmax), time of Cmax (tmax) and mean residence time (MRT) of the drug formulations were also statistically significant. Coated amoxicillin is suitable for in-feed administration to pigs and, thanks to its higher oral bioavailability compared to the not coated compound; it may be more effective for the treatment of susceptible infections. The bioavailability of the coated formulation most probably is referred to a greater stability in acid environment compared to not coated amoxicillin. Furthermore the protection of amoxicillin with a hydrophobic matrix matches with a reduced risk of cross-contamination and improves safety of feed manufacturing.