This study was conducted to reset the withdrawal time (WT) for amoxicillin (AMX) in pigs as a part of positive list system (PLS) program introduction. Forty-two healthy pigs were orally administered with AMX at doses of 10 mg/kg body weight (BW) (AMX-1, n=20) and 20 mg/kg BW (AMX-2, n=20), twice daily for 5 days, respectively. After the treatment, tissue samples were collected from four pigs at 1, 3, 5, 7 and 14 days post-administration, respectively. Based on a previously established analysis method, residual AMX concentrations in pig tissues were determined using LC-MS/MS. In both AMX-1 and AMX-2 groups, AMX levels in all tissues except fat was below the limit of quantification (LOQ) at one day after the final administration. According to the European Medicines Agency’s guideline on determination of withdrawal periods, the withdrawal periods for AMX-1 and AMX-2 in fat tissue were established as 0 and 2 days, respectively. In conclusion, the estimated WT of AMX in edible tissues of pigs is shorter than the current WT recommendation of 5 days for AMX.

Amoxicillin, a well-known antibiotic, has a broad spectrum against gram-negative and gram-positive bacteria. This experiment was conducted in order to investigate the effect of micronized and non-micronized amoxicillin prepared using different comminution techniques on change in blood concentration of rats. Forty adult male Sprague Dawley rats (6~7 weeks of age, body weight 128.3 ± 10.7 g) were randomly allocated to two treatment groups: micronized amoxicillin (MA) group treated with micronized amoxicillin trihydrate powder (particle size, over 90% of 10 μm), non-micronized amoxicillin (NMA) group treated with non-micronized amoxicillin trihydrate powder (particle size, over 70% of 100 μm), given 480 mg/kg body weight once daily for four days. The results showed a significant increase in serum concentration in the MA group on days 3 and 4, compared to the NMA group (P<0.05). In particular, serum concentration of the MA group on day 4 was increased almost two times that of the NMA group. The results indicate that due to the increase of the drug’s oral bioavailability, higher serum concentration would be achieved with the micronized amoxicillin trihydrate than with the non-micronized drug.