Amoxicillin concentrations were determined by two independent laboratories for a pig starter feed medicated from a coated amoxicillin premix. The analytical method was previously transferred from one laboratory to the other one. The data between the two laboratories were consistent, showing ruggedness of the assay. Mean amoxicillin feed concentrations before and after pelletization were higher than 90% of the theoretical content, confirming satisfactory stability of this active ingredient in the coated form tested.

A simple, robust, and rapid reversedphase high‐performance liquid chromatographic method for the analysis of demeclocycline and its impurities is described. Chromatographic separations were achieved on a Symmetry Shield RP8 (75 mm × 4.6 mm, 3.5 μm) column kept at 40°C. The mobile phase was a gradient mixture of acetonitrile, 0.06 M sodium edetate (pH 7.5), 0.06 M tetrapropylammonium hydrogen sulphate (pH 7.5) and water, A (2:35:35:28 v/v/v/v) and B (30:35:35:0 v/v/v/v) pumped at a flow rate of 1 mL/min. UV detection was performed at 280 nm. The developed method was validated according to the ICH guidelines for specificity, limit of detection, limit of quantification, linearity, precision, and robustness. An experimental design was applied for robustness study. Results show that the peak shape, chromatographic resolution between the impurities, and the total analysis time are satisfactory and better than previous methods. The method has been applied for the analysis of commercial demeclocycline bulk samples available on the market.