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Azithromycin hydrates-implications of processing-induced phase transformations.

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  • 1Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota, 55455.

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Azithromycin (AZI) can form different solid states, including sesquihydrate (SH), during processing. Understanding these azithromycin phase transitions is crucial for drug product stability and characterization.

Keywords:
HydrationX-ray powder diffractometryamorphouscrystal structuredehydrationphysical characterizationthermal analysistransformationtransitionwater sorption

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Area of Science:

  • Pharmaceutical Sciences
  • Solid-State Chemistry
  • Materials Science

Background:

  • Commercial azithromycin (AZI) solid dosage forms are labeled as monohydrate (MH) or dihydrate (DH).
  • AZI sesquihydrate (SH) has been observed in drug products, suggesting processing-induced phase transformations.
  • Understanding AZI solid-state behavior is critical for drug formulation and stability.

Purpose of the Study:

  • To prepare and characterize azithromycin sesquihydrate (SH).
  • To elucidate the solid-state transition pathways of AZI SH with other AZI phases (MH, DH, amorphous).
  • To develop methods for characterizing AZI in drug products containing crystalline excipients.

Main Methods:

  • Controlled dehydration and heating experiments to induce phase transitions.
  • X-ray diffraction (XRD) for solid-state characterization.
  • Pattern subtraction techniques for analyzing AZI in complex drug formulations.

Main Results:

  • Dihydrate (DH) dehydration yielded an isomorphic dehydrate (<80°C) or SH (≥80°C).
  • SH transformed to an amorphous form via an intermediate isomorphic dehydrate upon heating or low humidity exposure.
  • Monohydrate (MH) dehydration directly resulted in amorphization without intermediate crystalline anhydrates.
  • XRD pattern subtraction enabled AZI characterization in drug products despite crystalline excipients.

Conclusions:

  • Azithromycin (AZI) exhibits complex solid-state transitions, including the formation of sesquihydrate (SH) under specific conditions.
  • Distinct dehydration and amorphization pathways exist for AZI dihydrate (DH) and monohydrate (MH).
  • XRD pattern subtraction is an effective method for characterizing AZI solid forms within drug products.