Pirenoxine sodium, also known as pirfenidone sodium, is a heterocyclic organic compound with a molecular formula of C16H8N2O5·Na. It is the sodium salt form of pirenoxine, which is a pyridone derivative. The compound is typically a yellow to orange-yellow crystalline powder. Pirenoxine sodium is primarily used as an active pharmaceutical ingredient (API) in ophthalmic solutions for the treatment and prevention of senile cataracts. Its proposed mechanism of action involves competitively inhibiting quinones, which are thought to contribute to lens protein denaturation and aggregation in cataract formation. It is marketed under various brand names as an anti-cataract agent. As a registered drug substance, it is also relevant in pharmaceutical quality control. Pirenoxine and its related compounds (such as degradation products or process impurities) are subjects of analytical method development, requiring high-purity reference standards for identification and quantification in drug products.