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Identifying Optimal Drug Loading in Stable Amorphous Solid Dispersion Formulations: A Rheological Approach.
Sagar Narala1, Fengyuan Yang2, Kapish Karan1
1Ashland Specialty Ingredients, Wilmington, DE, 19808, United States of America.
Formulation scientists can determine optimal polymer/API ratios for stable amorphous drug systems using rheological studies. This research highlights how drug solubility in copovidone impacts the physical stability of amorphous nifedipine formulations.
Area of Science:
- Pharmaceutical Sciences
- Materials Science
Background:
- Synthetic polymers like copovidone enhance drug formulations via controlled release, bioavailability, and stability.
- Hot-melt extrusion (HME) uses copovidone to improve solubility of active pharmaceutical ingredients (APIs).
- Challenges include optimizing copovidone/API ratios and ensuring long-term stability of amorphous APIs.
Purpose of the Study:
- To assess the solubility and miscibility of crystalline nifedipine in copovidone.
- To develop stable amorphous polymer/API systems.
- To determine the optimal copovidone/API composition for nifedipine formulations.
Main Methods:
- Produced amorphous copovidone/nifedipine extrudates (10-60% w/w) using HME.
- Characterized extrudates using differential scanning calorimetry (DSC) and X-ray diffraction (XRD).
- Evaluated extrudate stability and homogeneity via rheological temperature cycles.
Main Results:
- All extrudates were amorphous, confirmed by DSC and XRD, irrespective of drug loading.
- Rheological studies indicated homogeneity at low drug loads, heterogeneity at medium loads, and API nucleus formation at high loads.
- Higher drug loads resulted in poor physical stability and API recrystallization during storage.
Conclusions:
- Rheological studies aid in creating semi-phase diagrams for optimal polymer/API composition.
- Thermodynamic stability is formulation-dependent, emphasizing the need to determine API solubility in the polymer.
- Optimal formulation composition is critical for achieving stable amorphous drug systems.
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