Does Media Choice Matter When Evaluating the Performance of Hydroxypropyl Methylcellulose Acetate Succinate-Based...

Area of Science:

• Pharmaceutical Sciences
• Polymer Chemistry
• Drug Delivery Systems

Background:

• Hydroxypropyl methylcellulose acetate succinate (HPMCAS) is crucial for amorphous solid dispersions (ASDs) due to its pH-dependent solubility.
• The influence of solution properties beyond pH, such as buffer capacity, on HPMCAS dissolution in ASDs is not fully understood.

Purpose of the Study:

• To investigate the rate-limiting factors for drug and HPMCAS release from ASDs.
• To elucidate the impact of buffer capacity and drug type on HPMCAS dissolution and gel layer properties.

Main Methods:

• Formulation of ASDs with indomethacin and indomethacin methyl ester using HPMCAS.
• Measurement of surface area normalized release rates in various media.
• Determination of HPMCAS gel layer apparent pH using pH-sensitive dyes.
• Gravimetric measurement of water uptake into ASDs.

Main Results:

• For neat HPMCAS, dissolution rate is limited by solubility at the interface, influenced by a lower gel layer pH dependent on buffer capacity.
• HPMCAS release rate controls drug release in ASDs, with drugs reducing polymer release, especially indomethacin methyl ester.
• Drug impact on release rates is diminished in low buffer capacity media, indicating altered rate-limiting steps for HPMCAS dissolution.

Conclusions:

• The study provides fundamental insights into acidic polymer dissolution for ASDs, considering both drug-free and drug-loaded systems.
• Understanding the interplay between buffer capacity, gel layer pH, and drug presence is key for designing ASDs.
• Findings can aid in developing more physiologically relevant *in vivo* dissolution testing for ASD formulations.