The antihypertensive drug substance amlodipine besylate crystallizes in two stable crystal forms, an anhydrate and a hitherto
unknown monohydrate. Both forms have been characterized by thermal analysis, X-ray powder diffractometry, FTIR- and FT Raman
spectroscopy. Moisture sorption- and desorption investigations reveal their unusual physical stability in a broad range of
relative humidities. The monohydrate forms an isomorphic dehydrate upon dehydration, which was elucidated by variable temperature
X-ray powder diffractometry. Physico-chemical properties as well as relative stabilities of the crystal forms are described
and discussed based on a comprehensive analytical identification, and enable an estimation of practical relevance for manufacturing
of amlodipine besylate solid dosage forms.