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Area of Science:

  • Materials Science
  • Pharmaceutical Science
  • Physical Chemistry

Background:

  • Pharmaceutical dispersions are crucial for drug delivery.
  • Understanding structural relaxation is key to predicting drug stability and preventing crystallization.
  • Nifedipine (NIF) dispersions with polymers like poly(vinyl) pyrrolidone (PVP) and hydroxypropyl methylcellulose acetate succinate (HPMCAS) are common.

Purpose of the Study:

  • To characterize structural relaxation in NIF-polymer dispersions using dielectric spectroscopy.
  • To investigate the influence of polymer type and concentration on molecular mobility and physical stability.
  • To apply the time-temperature superposition principle to these glassy pharmaceutical systems.

Main Methods:

  • Dielectric spectroscopy was employed to measure the dielectric response of NIF and its dispersions with PVP and HPMCAS.
  • The time-temperature superposition principle was tested for pure NIF and its dispersions.
  • Structural relaxation times and fragility were analyzed as a function of polymer concentration and temperature.

Main Results:

  • The time-temperature superposition principle was valid for pure NIF and its dispersions.
  • A limited time-temperature-concentration superposition was observed for the structural relaxation regime.
  • Stronger drug-polymer hydrogen bonding (NIF-PVP > NIF-HPMCAS > NIF) correlated with reduced molecular mobility and improved physical stability (delayed crystallization).
  • Increased polymer concentration led to longer relaxation times, indicating decreased molecular mobility.
  • Fragility, the temperature dependence of relaxation time, was independent of polymer concentration.

Conclusions:

  • Dielectric spectroscopy and the superposition principle provide valuable insights into structural relaxation in pharmaceutical dispersions.
  • Drug-polymer hydrogen bonding strength is a critical factor in enhancing the physical stability of amorphous solid dispersions.
  • This study demonstrates the first application of superposition principles to characterize structural relaxation in glassy pharmaceutical dispersions.