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Related Experiment Videos

Microenvironmental pH and microviscosity inside pH-controlled matrix tablets: an EPR imaging study.

Stefanie Siepe1, Werner Herrmann, Hans-Hubert Borchert

  • 1Novartis Pharma AG, Technical R and D, CH-4002 Basel, Switzerland. stefanie.siepe@novartis.com

Journal of Controlled Release : Official Journal of the Controlled Release Society
|February 16, 2006
PubMed
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Fumaric acid effectively maintained reduced pH within HPMC matrix tablets, unlike citric acid which diffused out. Electron paramagnetic resonance imaging (EPRI) enabled spatial monitoring of pH and microviscosity for formulation optimization.

Area of Science:

  • Pharmaceutical Sciences
  • Physical Chemistry
  • Materials Science

Background:

  • pH modifiers enhance dissolution rates of weakly basic drugs in sustained release dosage forms.
  • Hydroxypropylmethylcellulose (HPMC) matrix tablets are common sustained release systems.
  • Understanding internal microenvironment changes is crucial for formulation design.

Purpose of the Study:

  • To investigate the spatial and temporal changes in micro-environmental pH and viscosity within HPMC matrix tablets using pH modifiers.
  • To evaluate the impact of different organic acids (fumaric, citric, succinic) as pH modifiers.
  • To demonstrate the utility of Electron Paramagnetic Resonance Imaging (EPRI) for non-invasive formulation analysis.

Main Methods:

  • Utilized Electron Paramagnetic Resonance Imaging (EPRI) to spatially monitor micro-environmental pH (pH(M)) and rotational correlation time (tau(R), related to microviscosity).

Related Experiment Videos

  • Employed 4-(methylamino)-2-ethyl-5,5-dimethyl-4-pyridine-2-yl-2,5-dihydro-1H-imidazole-1-oxyl (MEP) as a spin label.
  • Incorporated fumaric, citric, and succinic acids as pH modifiers in HPMC matrix tablets.

    • Main Results:

    • Fumaric and citric acids initially reduced pH(M) similarly; citric acid diffused out with hydration, increasing outer layer pH(M).
    • Fumaric acid maintained a consistently reduced pH(M) throughout the tablet.
    • Succinic acid showed less effective pH reduction due to its lower acidic strength.
    • Water-soluble acids increased water penetration, rapidly decreasing tau(R) upon hydration; pH modifiers had minor impact on tau(R) post-hydration.

    Conclusions:

    • Fumaric acid is a suitable pH modifier for sustained pH reduction in HPMC matrices.
    • EPRI is a powerful, non-invasive tool for spatially resolved monitoring of pH(M) and tau(R) in solid dosage forms.
    • EPRI facilitates the optimization of pH-controlled drug delivery formulations.