Mutual Influence of Mannitol and Trehalose on Crystallization Behavior in Frozen Solutions
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Phase separation of trehalose during freeze-drying could render it ineffective as a lyoprotectant. The bulking agent, mannitol, on the other hand, should crystallize readily upon freezing. It is therefore imperative to understand the mutual interaction of these sugars during freezing to ensure preservation of the API during freeze-drying.
We investigated the effect of mannitol to trehalose ratio (R) on the crystallization behavior of both solutes using Differential Scanning Calorimetry, X-Ray Crystallography and FTIR Spectrosopy during controlled freezing and annealing.
When R = 1, crystallization of both mannitol (as hemihydrate) and trehalose (as α-anhydrate) were observed. When R ≥ 1, extent of mannitol crystallization was directly proportional to the value of R. When R < 1, trehalose completely suppressed mannitol crystallization. At R > 1, the freeze concentrate was heterogeneous and characterized by two glass transitions – the lower temperature transition (Tg”) attributed to systems containing “extra” unfrozen water. When heated above Tg”, crystallization of mannitol and the associated unfrozen water resulted in Tg’ (glass transition temperature of the freeze-concentrate).
R and not the total solute concentration, dictates the composition of the freeze concentrate as well as the physical stability of the excipients
Key Wordscrystallization frozen IR spectroscopy mannitol microscopy trehalose X-ray diffractometry
Active pharmaceutical ingredient
Differential scanning calorimetry
Fourier transform infrared spectroscopy
Powder X-ray Diffractometry
ACKNOWLEDGMENTS AND DISCLOSURES
This research was funded by an NSF grant (CBET-1335936) to A.A. The authors are grateful to Dr. Seema Thakral for guidance while performing the powder X-ray diffraction. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.
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