An Insight into Eudragit S100 Preserving Mechanism of Cinnarizine Supersaturation

Impact of HPMCAS Grade on the Release of Weakly Basic Drugs from Amorphous Solid Dispersions

Oppositely charged species can form electrostatic interactions in aqueous solution, and these may lead to reduced solubility of the interacting components. Herein, insoluble complex formation between the lipophilic weakly basic drugs, cinnarizine or loratadine, and the enteric polymer, hydroxypropyl methylcellulose acetate succinate (HPMCAS), was studied and used to better understand drug and polymer release from their corresponding amorphous solid dispersions (ASDs). Surface area normalized release experiments were performed at various pH conditions for three different grades of HPMCAS, LF, MF and HF, as well as their ASDs. Both polymer and drug release rates were measured for the ASDs. Complexation tendency was evaluated by measuring the extent of polymer loss from the aqueous phase in the presence of the drug. Results showed that release from ASDs with HPMCAS-LF was less impacted by the presence of a cationic form of the drug than ASDs prepared with the HF grade. Furthermore, an increase in pH, leading to a reduction in the extent of ionized drug also led to an improvement in release rate. These observations provide a baseline to understand the role of drug-polymer electrostatic interactions on release from ASDs formulated with HPMCAS. Future studies should focus on adding complexity to media conditions by employing simulated intestinal fluids with solubilizing components.

Interplay of Drug-Polymer Interactions and Release Performance for HPMCAS-Based Amorphous Solid Dispersions

The interplay between drug and polymer chemistry and its impact on drug release from an amorphous solid dispersion (ASD) is a relatively underexplored area. Herein, the release rates of several drugs of diverse chemistry from hydroxypropyl methylcellulose acetate succinate (HPMCAS)-based ASDs were explored using surface area normalized dissolution. The tendency of the drug to form an insoluble complex with HPMCAS was determined through coprecipitation experiments. The role of pH and the extent of drug ionization were probed to evaluate the role of electrostatic interactions in complex formation. Relationships between the extent of complexation and the drug release rate from an ASD were observed, whereby the drugs could be divided into two groups. Drugs with a low extent of insoluble complex formation with HPMCAS tended to be neutral or anionic and showed reasonable release at pH 6.8 even at higher drug loadings. Cationic drugs formed insoluble complexes with HPMCAS and showed poor release when formulated as an ASD. Thus, and somewhat counterintuitively, a weakly basic drug showed a reduced release rate from an ASD at a bulk solution pH where it was ionized, relative to when unionized. The opposite trend was observed in the absence of polymer for the neat amorphous drug. In conclusion, electrostatic interactions between HPMCAS and lipophilic cationic drugs led to insoluble complex formation, which in turn resulted in ASDs with poor release performance.