Amorphous solid dispersions miscibility significantly dictates pharmaceutical formulation success for poorly water-soluble drugs. Hydrogen bonds (H-bonds) play a pivotal role in stabilizing these systems and influencing drug release profiles. Recent research explored specific molecular interactions between Diflunisal (DIF) and the polymer Eudragit S100 (ES100) to understand these complex dynamics. Because ES100 features both H-bond-donor and H-bond-acceptor groups, it provides a unique environment for studying molecular miscibility.

Enhancing Amorphous Solid Dispersions Miscibility Through H-Bonding

Researchers utilized solid-state NMR relaxometry and ssNMR spectroscopy to evaluate how drug-polymer interactions affect formulation success. They found that the carboxyl groups in Eudragit S100 act as H-bond donors to the carbonyl groups of Diflunisal derivatives. This interaction promotes homogeneous mixing across all tested dispersions. Interestingly, the study discovered that native Diflunisal achieves a lower maximum drug loading (25 wt %) compared to certain derivatives like methoxy DIF (35 wt %). This difference arises from a competition between intermolecular and intramolecular H-bonds within the drug molecule.

Furthermore, the study contrasted these findings with polymers like PVPVA, which only possess H-bond-acceptor groups. When using PVPVA, the availability of H-bond-donor groups on the drug remains essential for stable interaction. Conversely, when employing a dual-purpose polymer like ES100, the availability of H-bond-acceptor groups on the API becomes the critical factor. These insights help formulation scientists predict the phase behavior of amorphous solid dispersions more accurately. Consequently, selecting the right polymer based on the drug's functional groups can maximize loading capacity and long-term stability.

Frequently Asked Questions

How does hydrogen bonding improve drug stability?

Hydrogen bonds create strong intermolecular links between the drug and the polymer. These interactions inhibit the molecular mobility of the drug, which prevents it from recrystallizing during storage. Therefore, the formulation remains in a stable amorphous state for longer periods.

What is the difference between ES100 and PVPVA in ASDs?

Eudragit S100 (ES100) acts as both a hydrogen bond donor and a hydrogen bond acceptor. PVPVA, however, only functions as an H-bond acceptor. Consequently, ES100 offers more interaction pathways for drugs with diverse functional groups, often improving miscibility where other polymers might fail.

Why did native Diflunisal have lower drug loading than its derivatives?

Native Diflunisal forms stable six-membered rings through internal hydrogen bonding. This internal competition limits the drug's ability to bond with the polymer. Because the derivatives reduce this internal bonding, they can form more interactions with the polymer, allowing for higher drug loading.

Disclaimer: This content is for informational and educational purposes only. It does not constitute professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Refer to the latest local and national guidelines for clinical practice.

References

Cools L et al. Drug-Polymer Interactions and Molecular Miscibility in Amorphous Solid Dispersions: The Duality of Hydrogen Bond-Donor Groups. Mol Pharm. 2026 Mar 12. doi: 10.1021/acs.molpharmaceut.5c01572. PMID: 41818776.

Baghel S, Cathcart H, O'Reilly NJ. Polymeric Amorphous Solid Dispersions: A Review of Physico-Chemical Characterisation and Formulations Strategies. J Pharm Sci. 2016.

Rams-Baron M, et al. Molecularly Dispersed Systems: The Role of Hydrogen Bonding. Pharmaceutics. 2018.