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To the Editor:—
An explanation for the efficacy of sulfapyridine and sulfathiazole which I have not seen in print is suggested by an examination of their structural formulas:Now, sulfapyridine differs from the parent sulfanilamide by having a pyridine nucleus attached to the amido group. This pyridine nucleus is present in the quinoline alkaloids, such as quinine, and also in the synthetic ethyl hydrocupreine hydrochloride. These are toxic to pneumococci, and the effectiveness of sulfapyridine may possibly be due in some measure to the added pyridine nucleus.If sulfur is substituted for an ethylene linkage in a cyclic compound, the properties are not changed much. Thus, thiophene and benzene have properties so close that it is very difficult to separate them. In the same fashion, thiazole differs little from pyridine in chemical and physical properties.Thus, one would expect sulfathiazole to have about the same chemical properties, and therefore pharmacologic action,
Abrahamson EM. STRUCTURAL RELATIONSHIPS OF SULFAPYRIDINE AND SULFATHIAZOLE. JAMA. 1941;116(24):2713. doi:10.1001/jama.1941.02820240073023