Abstract
During in-use stability testing of cefixime granules for oral suspension, an impurity with a relative retention time of 0.19 was consistently detected and increased during storage. To ensure regulatory compliance and patient safety, the impurity was structurally identified and toxicologically qualified. A laboratory-scale formulation and commercial products were studied under refrigerated and ambient conditions. The impurity was isolated by automated fraction collection and characterised by liquid chromatography-mass spectrometry and tandem mass spectrometry. Kinetic evaluation showed pseudo-first-order formation, with faster accumulation at ambient temperature. The impurity was identified as a γ-lactone degradation product of cefixime, present as multiple stereoisomers stabilised under acidic conditions. In silico toxicological assessment using complementary platforms indicated no additional structural alerts, no mutagenic potential, and negligible acute toxicity. The impurity forms only after prolonged storage of reconstituted suspensions and is classified as an ICH M7 Class 5 impurity, requiring no further genotoxicity testing. The applied analytical-computational workflow provides an efficient approach for impurity qualification in β-lactam antibiotics.