Famotidine EP Impurity H, chemically identified as [2-[(Diaminomethylidene)amino]thiazol-4-yl]methyl carbamimidothioate dihydrochloride and commonly referred to as Famotidine Isothiourea Impurity, is a guanidinothiazole-based isothiourea impurity of Famotidine, with molecular formula C₆H₁₀N₆S₂·2HCl and molecular weight 303.22 g/mol (free base 230.31 g/mol). Structurally, this compound is S-[(2-guanidinothiazol-4-yl)methyl]isothiourea, a key early intermediate of Famotidine synthesis formed from 4-(chloromethyl)-2-guanidinothiazole and thiourea; it is subsequently S-alkylated to build the propanenitrile side chain that is finally converted to the sulfamoyl amidine. Its presence in the API therefore indicates intermediate carryover, and its hydrolysis to the corresponding thiol also leads to the disulfide Impurity E. This makes it a critical reference marker for process-related impurity monitoring and reaction-completeness verification throughout Famotidine API manufacturing. Manufactured at Chemicea under precisely controlled synthetic and purification protocols, this reference standard supports impurity identification, method validation (AMV), and quality-control testing in accordance with EP monograph requirements, and is routinely applied in ANDA and DMF regulatory submissions. Each batch is supplied with a comprehensive Certificate of Analysis supported by HPLC, ¹H-NMR, and Mass Spectrometry characterization data, ensuring dependable analytical traceability for pharmaceutical R&D and QC laboratories worldwide. CAS No. 88046-01-9 (dihydrochloride; free base CAS No. 106649-96-1) | Explore complete technical documentation, Safety Data Sheet (SDS), and pricing.