A cross-polarization magic-angle spinning 13C NMR characterization of the stable solid-state forms of cimetidine.

Proton decoupled, cross-polarization magic-angle spinning 13C NMR spectra of four polymorphic forms (A, B, C, and D) and a monohydrate form (M1) of the histamine H2 antagonist cimetidine were obtained, and the chemical shifts of the various forms were tabulated. A modified polarization inversion pulse sequence was used to distinguish quaternary, methine, methylene, and methyl carbon resonances and thereby assist spectral assignment. It is also shown that the solid-state form of cimetidine in a commercial formulation can be reliably ascertained by NMR, despite the presence in the spectrum of signals from organic excipients that are much more intense than those from the compound.