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Hydrochlorides, hydrates, hydronitrate, and an unanticipated hydrolysis product of famotidine

Year: 2026
Type: article
Abstract: This article contributes to the development of Paper-Based Analytical Devices (PADs), a low-cost field-friendly platform for screening low-quality medicines. Our investigation focuses on famotidine, the active pharmaceutical ingredient (API) in Pepcid AC [an over-the-counter medicine used to treat gastroesophageal reflux disease (GERD)]. We report the successful isolation and characterization of several new crystalline forms of famotidine, focusing on the API itself rather than its PAD-activated colored complex. These forms include a famotidine hydrochloride polymorph, C 6 H 14 N 7 O 2 S + ·Cl − ( I ), a famotidine hydrochloride hemihydrate salt, C 6 H 14 N 7 O 2 S + ·Cl − ·0.5H 2 O ( II ), and a famotidine nitrate salt, C 6 H 14 N 7 O 2 S + ·NO 3 − ( III ). Unexpectedly, we also characterized a hydrolyzed famotidine complex, N -(diaminomethylene)-4-({[3-oxo-3-(sulfamoylamino)propyl]sulfanyl}methyl)thiazol-2-aminium chloride sesquihydrate, C 8 H 15 N 6 O 3 S 3 + ·Cl − ·1.5H 2 O ( IV ). The crystal structures reveal significant solid-state diversity: hemihydrate salt II exhibits two symmetry-independent famotidine hydrochloride molecules per asymmetric unit, while sesquihydrate salt IV shows four crystallographically-independent hydrochloride molecules and six symmetry-independent water molecules per standard unit. All four complexes display extensive hydrogen-bonded networks in the solid state. The detailed structural characterization of these crystalline complexes generates fundamental solid-state chemistry data; this knowledge is essential for predicting and controlling the drug performance and formulation stability of famotidine and crucially informs our development of PADs.
DOI: 10.1107/s2053229626004122
Language: English
Open Access status: hybrid
Estimated APC paid: $3,950
OpenAlex ID: W7155553671
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