Deciphering magnesium stearate thermotropic behavior

[Display omitted] Magnesium stearate (MgSt) is the most commonly used excipient for oral solid dosage forms, yet there is significant commercial physicochemical variability that can lead to variable performance of critical product attributes. Differential scanning calorimetry (DSC) is often used as...

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Published inInternational journal of pharmaceutics Vol. 548; no. 1; pp. 314 - 324
Main Authors Haware, Rahul V., Vinjamuri, Bhavani Prasad, Sarkar, Amrita, Stefik, Morgan, Stagner, William C.
Format Journal Article
LanguageEnglish
Published Netherlands Elsevier B.V 05.09.2018
Subjects
Magnesium stearate mesophases
Temperature dependent small angle X-ray scattering (SAXS)
Thermal analysis
Thermotropic reversibility
Thermotropic reversibility
Thermal analysis
Temperature dependent small angle X-ray scattering (SAXS)
Magnesium stearate mesophases
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Summary:[Display omitted] Magnesium stearate (MgSt) is the most commonly used excipient for oral solid dosage forms, yet there is significant commercial physicochemical variability that can lead to variable performance of critical product attributes. Differential scanning calorimetry (DSC) is often used as a quality control tool to characterize MgSt, but little data is available regarding the physicochemical relevance for the DSC thermograms. The main aim of this study was to decipher MgSt’s complex thermotropic behavior using DSC, thermogravimetric analysis, capillary melting point, polarized hot-stage microscopy, and temperature dependent small-angle X-ray scattering (SAXS) and assign physicochemical relevance to the DSC thermograms. Several DSC thermal transitions are irreversible after the first heating cycle of a heat-cool-heat-cool-heat cycle. Interestingly, after the first heat cycle, the complex cool-heat-cool-heat DSC thermograms were highly reproducible and exhibited 6 reversible exothermic-endothermic conjugate pairs. SAXS identified 5 distinct mesophases at different temperatures with Phase C′ persisting to 250 °C. MgSt maintained molecular ordering beyond 276 °C and did not undergo a simple melting phenomena reported elsewhere. This research serves as a starting point to design heat-treatment strategies to create more uniform MgSt starting material.
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ISSN:0378-5173
1873-3476
DOI:10.1016/j.ijpharm.2018.07.001