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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
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Investigating gabapentin polymorphism using solid-state NMR spectroscopy.

Kassibla E Dempah1, Dewey H Barich, Aditya M Kaushal

  • 1Department of Pharmaceutical Sciences, University of Kentucky, Lexington, Kentucky, USA.

AAPS Pharmscitech
|November 27, 2012
PubMed
Summary
This summary is machine-generated.

Solid-state NMR spectroscopy (SSNMR) identified four gabapentin crystalline forms. SSNMR can predict gabapentin stability in formulated products, with longer 1H T1 values indicating greater stability.

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Area of Science:

  • Pharmaceutical Sciences
  • Solid-State Chemistry
  • Analytical Chemistry

Background:

  • Gabapentin exhibits polymorphism, with different crystalline forms impacting its stability and performance.
  • Understanding the physical forms of active pharmaceutical ingredients (APIs) is crucial for drug development and formulation.
  • Solid-state characterization techniques are essential for identifying and controlling API physical forms.

Purpose of the Study:

  • To identify the physical forms of gabapentin under various preparation conditions.
  • To investigate the influence of milling and excipients on gabapentin's physical form and stability.
  • To evaluate the utility of solid-state NMR spectroscopy (SSNMR) in predicting gabapentin stability.

Main Methods:

  • Powder X-ray diffraction (PXRD) and solid-state NMR spectroscopy (13C SSNMR, 1H T1 relaxation measurements) were employed.
  • Gabapentin samples were prepared using recrystallization, spray drying, dehydration, and milling.
  • Ball-milling of gabapentin with and without hydroxypropylcellulose (HPC), followed by stress storage, was performed.
  • High-performance liquid chromatography (HPLC) was used to quantify degradation products.

Main Results:

  • Four distinct crystalline forms of gabapentin were identified: form I (monohydrate), form II (stable ambient form), form III (milled/recrystallized form), and an isomorphous desolvate.
  • Ball-milling gabapentin, especially with HPC, induced a transition to form III and significantly reduced its stability, as indicated by shorter 1H T1 values.
  • Samples with longer 1H T1 values exhibited substantially greater stability against degradation compared to those with shorter T1 values.

Conclusions:

  • SSNMR, particularly 1H T1 relaxation measurements, can effectively differentiate gabapentin physical forms and predict its solid-state stability.
  • The presence of HPC during milling can influence the crystalline form and decrease gabapentin stability.
  • These findings highlight the importance of solid-state characterization for controlling API physical form and ensuring drug product stability.