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Factors Affecting Dissolution: Polymorphism, Amorphism and Pseudopolymorphism01:21

Factors Affecting Dissolution: Polymorphism, Amorphism and Pseudopolymorphism

Polymorphism refers to the existence of a drug substance in multiple crystalline forms, known as polymorphs. Recently, this term has been expanded to include solvates (forms containing a solvent), amorphous forms (non-crystalline forms), and desolvated solvates (forms from which the solvent has been removed).
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Changes in polymorphic forms can significantly influence the bioavailability of poorly soluble drugs. Although the FDA defines pharmaceutical equivalence based on having the same active ingredient, dosage form, and route of administration, it does not automatically disqualify products with different polymorphic forms. This means two products with different polymorphs can still be deemed pharmaceutically equivalent. However, polymorphic differences can affect properties like wettability,...
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Isomerism in Complexes
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Structural study of polymorphs and solvates of finasteride.

Abdullah Othman1, John S O Evans, Ivana Radosavljevic Evans

  • 1Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK.

Journal of Pharmaceutical Sciences
|April 25, 2007
PubMed
Summary

New solid forms of finasteride were characterized using NMR and XRD. Researchers identified novel anhydrous and solvate forms, revealing common structural features and solvent mobility in crystal channels.

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Area of Science:

  • Solid-state chemistry
  • Crystallography
  • Pharmaceutical science

Background:

  • Finasteride exists in various polymorphic forms, impacting its pharmaceutical properties.
  • Understanding these solid forms is crucial for drug formulation and stability.
  • Previous characterization of finasteride forms was limited, particularly regarding solvates.

Purpose of the Study:

  • To characterize new solid-state forms of finasteride.
  • To determine the crystal structures of finasteride solvates.
  • To investigate the structural similarities and differences among various finasteride forms.

Main Methods:

  • Nuclear Magnetic Resonance (NMR) spectroscopy (13C CPMAS, MAS proton, direct polarization 13C)
  • X-ray Diffraction (XRD) (powder and single-crystal)
  • Thermogravimetric Analysis (TGA)

Main Results:

  • Characterization of new anhydrous (Form X) and solvate forms of finasteride.
  • Determination of crystal structures for dioxane, isopropanol (IPA), and tetrahydrofuran (THF) solvates, revealing a common structure with disordered solvent molecules in channels.
  • Identification of most solvates as hemihydrates with a 2:1 finasteride:solvent molar ratio, exhibiting high solvent mobility and characteristic NMR signals.

Conclusions:

  • Multiple new solid forms of finasteride have been identified and structurally elucidated.
  • A common structural motif exists among several finasteride solvates, characterized by disordered solvent molecules.
  • NMR and XRD are effective tools for distinguishing and characterizing finasteride polymorphs and solvates, with solvent mobility being a key feature.