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Updated: Jul 15, 2026

Coherent anti-Stokes Raman Scattering (CARS) Microscopy Visualizes Pharmaceutical Tablets During Dissolution
Published on: July 4, 2014
Probing pseudopolymorphic transitions in pharmaceutical solids using Raman spectroscopy: hydration and dehydration of
Ana M Amado1, Mariela M Nolasco, Paulo J A Ribeiro-Claro
1Química-Física Molecular, Departamento de Química, FCTUC, Universidade de Coimbra, P-3004-535 Coimbra, Portugal.
Abstract:
Theophylline is known to undergo vapor phase induced hydrate-anhydrate pseudopolymorphic transformations, which can affect its bioavailability. In this work, the kinetics of the pseudopolymorphic transitions of theophylline crystals in different storage conditions is studied using a vibrational spectroscopic technique. While the hydration is a single-step process with a half-life time of ca. 5 h, the dehydration occurs through a two-step mechanism. In addition, the phase stability of hydrate-anhydrate systems in different relative humidity (RH) conditions was probed. The critical RH for anhydrous teophylline was found to be at ca. 79%, while the critical RH for dehydration is ca. 30%.
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