The polymorphism of cimetidine.

High resolution FT-IR data are given on five known and two uncharacterized modifications of cimetidine. On the basis of the chronological order of publications and the usual nomenclature, an attempt is made to clear up the uncertainty concerning the names of the various modifications. An attempt is made to rationalize the spectroscopic data characterizing the given modifications. The anhydrous and the monohydrate modifications are discussed separately, together with those changes which occur on the dehydration of the monohydrates without melting.