The phthalylsulfathiazole API market is projected to grow from USD 777.9 million in 2025 to USD 1,162.6 million by 2035, at a CAGR of 4.1%. Purity ≥ 99% will dominate with a 65.0% market share, while gastrointestinal bacterial infection will lead the application segment with a 58.0% share.