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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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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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In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the...
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Phase I biotransformation reactions are integral to drug metabolism, predominantly involving oxidative, reductive, and hydrolytic transformations. Chief among these are oxidative reactions, which enhance the hydrophilicity of xenobiotics and introduce polar functional groups to facilitate their elimination from the body.
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When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
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A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
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The phase relationship between the pyrazinamide polymorphs α and γ.

Kangli Li1, Gabin Gbabode1, Maria Barrio2

  • 1Laboratoire SMS-EA3233, UFR des Sciences et Techniques, Universite de Rouen Normandie, Place Emile Blondel, 76821 Mont-Saint-Aignan, France.

International Journal of Pharmaceutics
|March 23, 2020
PubMed
Summary

This study defines the temperature and pressure conditions for pyrazinamide polymorphs. It reveals that pyrazinamide form α is stable at room temperature, while form γ is stabilized by high pressure.

Keywords:
Active pharmaceutical ingredientPressure–temperature phase diagramSolid–solid transitionSolubilitySpecific volumeThermal expansionVapor pressure

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Area of Science:

  • Pharmaceutical Science
  • Solid-State Chemistry
  • Materials Science

Background:

  • Pyrazinamide is a key drug for tuberculosis treatment, exhibiting multiple crystalline forms (polymorphs).
  • Polymorphism can impact drug solubility and formulation efficacy, necessitating understanding of different crystal forms.
  • Existing literature lacks defined equilibrium conditions for pyrazinamide polymorphs.

Purpose of the Study:

  • To determine the temperature and pressure equilibrium conditions between pyrazinamide's alpha (α) and gamma (γ) polymorphs, liquid, and vapor phases.
  • To quantify phase-change thermodynamic properties like enthalpy, entropy, and volume differences.
  • To establish the thermodynamic stability relationships between pyrazinamide polymorphs under varying conditions.

Main Methods:

  • Experimental determination of equilibrium temperature between α and γ polymorphs.
  • Measurement of vapor pressures and solubilities for different pyrazinamide phases.
  • High-pressure thermal analysis and construction of a pressure-temperature phase diagram.

Main Results:

  • The equilibrium temperature between pyrazinamide α and γ polymorphs was experimentally determined to be 392(1) K.
  • Form α was identified as the more stable polymorph at ambient temperature, based on vapor pressure and solubility data.
  • High-pressure studies indicated that form γ becomes stable at room temperature under pressures of 260 MPa.

Conclusions:

  • This research provides crucial thermodynamic data for understanding pyrazinamide's solid-state behavior.
  • The findings clarify the stability of different pyrazinamide polymorphs, with implications for drug formulation and manufacturing.
  • The study highlights the potential of pressure to stabilize otherwise metastable polymorphs for pharmaceutical applications.