Cytidine-5,6-d2 is a deuterium-labeled analog of cytidine, where hydrogen atoms at the 5 and 6 positions are replaced with deuterium. This stable isotope-labeled compound is primarily used in metabolic and pharmacokinetic studies, enabling precise tracking of cytidine uptake, distribution, and turnover in biological systems via mass spectrometry or NMR. The incorporation of deuterium enhances molecular stability, reducing metabolic degradation and improving detection sensitivity. Its high isotopic purity (>98%) ensures reliable experimental results, making it valuable for research in nucleoside biochemistry, drug development, and tracer studies. The compound is supplied as a lyophilized solid, ensuring stability and ease of handling under standard laboratory conditions.