L-Amoxicillin-d4 sodium is the deuterium-labeled version of L-Amoxicillin, an antibiotic effective against various bacterial infections. It is often used in combination with the β-lactamase inhibitor potassium clavulanate for enhanced antimicrobial efficacy. Analytical methods for related substances of L-Amoxicillin have been developed and validated following International Council for Harmonisation (ICH) guidelines to ensure effectiveness and accuracy in mixtures. Further analysis of L-Amoxicillin and its impurities during stress testing and stability studies provides support for optimizing its application.