Deconstructing HPMCAS: Excipient Design to Tailor Polymer-Drug Interactions for Oral Drug Delivery

Jeffrey M. Ting, Tushar S. Navale, Seamus D. Jones, Frank S. Bates, Theresa M. Reineke

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


Spray-dried dispersions (SDDs) are fascinating polymer-drug mixtures that exploit the amorphous state of a drug to dramatically elevate its apparent aqueous solubility above equilibrium. For practical usage in oral delivery, understanding how polymers mechanistically provide physical stability during storage and prevent supersaturated drugs from succumbing to precipitation during dissolution remains a formidable challenge. To this end, we developed a versatile polymeric platform with functional groups analogous to hydroxypropyl methyl cellulose acetate succinate (HPMCAS, a heterogeneous leading excipient candidate for SDDs) and studied its interactions with Biopharmaceutical Classification System Class II drug models probucol, danazol, and phenytoin at various dosages. By conducting reversible addition-fragmentation chain transfer polymerizations with monomeric components chemically analogous to HPMCAS, we synthetically dismantled the highly polydisperse architecture of HPMCAS into well-defined polymer systems (i.e., targetable Mn, < 1.3, tunable Tg). In the powdered SDD form, by wide-angle X-ray diffraction all HPMCAS analogs yielded amorphous danazol and phenytoin up to 50 wt % loading, whereas for probucol, hydrophobic methoxy functionality and high polymeric Tg were key to inhibit immediate partitioning into crystalline domains. Nonsink in vitro dissolution tests revealed distinct release profiles. The polymer containing only acetyl and succinoyl substituents spray-dried with probucol increased the area under the dissolution curve by a factor of 180, 112, and 26 over pure drug at 10, 25, and 50 wt % loading, respectively. For crystallization-prone danazol and phenytoin, we observed that the water-soluble polymer with hydroxyl groups inhibited crystal growth and enabled high burst release and supersaturation maintenance. Our findings provide fundamental insight into how excipient microstructures can complex with drugs for excipient formulation applications.

Original languageEnglish (US)
Pages (from-to)978-990
Number of pages13
JournalACS Biomaterials Science and Engineering
Issue number10
StatePublished - Oct 12 2015

Bibliographical note

Funding Information:
We acknowledge the financial support of The Dow Chemical Company in this study. We gratefully thank Prof. Marc A. Hillmyer and Prof. Timothy P. Lodge at the University of Minnesota, as well as Dr. Steven J. Guillaudeu, Dr. Robert L. Schmitt, and Dr. William W. Porter III at The Dow Chemical Company, for invaluable discussions and feedback. We also thank Ralm G. Ricarte for assisting with his expertise in SEM imaging, as well as Anatolii A. Purchel and Ziang Li for helpful discussions with FTIR analysis. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant 00006595. Parts of this work were carried out in the Characterization Facility at the University of Minnesota, a member of the NSF-funded Materials Research Facilities Network ( via the MRSEC program.


  • amorphous solid dispersions
  • oral drug delivery
  • polymer-drug interactions
  • precipitation inhibition

How much support was provided by MRSEC?

  • Shared

Reporting period for MRSEC

  • Period 2

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