Prediction and Construction of Drug-Polymer Binary System Thermodynamic Phase Diagram in Amorphous Solid Dispersions (ASDs)

Exploring the influence of hydrogen bond donor groups on the microstructure and intermolecular interactions of amorphous solid dispersions containing diflunisal structural analogues

Drug-polymer intermolecular interactions, and H-bonds specifically, play an important role in the stabilization process of a compound in an amorphous solid dispersion (ASD). However, it is still difficult to predict whether or not interactions will form and what the strength of those interactions would be, based on the structure of drug and polymer. Therefore, in this study, structural analogues of diflunisal (DIF) were synthesized and incorporated in ASDs with poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA) as a stabilizing polymer. The respective DIF derivatives contained different types and numbers of H-bond donor groups, which allowed to assess the influence of these structural differences on the phase behavior and the actual interactions formed in the ASDs. The highest possible drug loading of these derivatives in PVPVA were evaluated through film casting. Subsequently, a lower drug loading of each compound was spray dried. These spray dried ASDs were subjected to an in-depth solid-state nuclear magnetic resonance (ssNMR) study, including 1D spectroscopy and relaxometry, as well as 2D dipolar HETCOR experiments. The drug loading study revealed the highest possible loading of 50 wt% for the native DIF in PVPVA. The methoxy DIF derivative reached the second highest drug loading of 35 wt%, while methylation of the carboxyl group of DIF led to a sharp decrease in the maximum loading, to around 10 wt% only. Unexpectedly, the maximum loading increased again when both the COOH and OH groups of diflunisal were methylated in the dimethyl DIF derivative, to around 30 wt%. The ssNMR study on the spray dried ASD samples confirmed intermolecular H-bonding with PVPVA for native DIF and methoxy DIF. Studies of the proton relaxation decay times and 2D 1H-13C dipolar HETCOR experiments indicated that the ASDs with native DIF and methoxy DIF were homogenously mixed, while the ASDs containing DIF methyl ester and dimethyl DIF were phase separated at the nm level. It was established that, for these systems, the availability of the carboxyl group was imperative in the formation of intermolecular H-bonds with PVPVA and in the generation of homogenously mixed ASDs.

Polymer Characteristics for Drug Layering on Particles Using a Novel Melt Granulation Technology, MALCORE®

MALCORE®, a novel manufacturing technology for drug-containing particles (DCPs), relies on the melt granulation method to produce spherical particles with high drug content. The crucial aspect of particle preparation through MALCORE® involves utilizing polymers that dissolve in the melt component, thereby enhancing viscosity upon heating. However, only aminoalkyl methacrylate copolymer E (AMCE) has been previously utilized. Therefore, this study aims to discover other polymers and comprehend the essential properties these polymers need to possess. The results showed that polyvinylpyrrolidone (PVP) was soluble in the stearic acid (SA) melt component. FTIR examination revealed no interaction between SA and polymer. The phase diagram was used to analyze the state of the SA and polymer mixture during heating. It revealed the mixing ratio and temperature range where the mixture remained in a liquid state. The viscosity of the mixture depended on the quantity and molecular weight of the polymer dissolved in SA. Furthermore, the DCPs prepared using PVP via MALCORE® exhibited similar pharmaceutical properties to those prepared with AMCE. In conclusion, understanding the properties required for polymers in the melt granulation process of MALCORE® allows for the optimization of manufacturing conditions, such as temperature and mixing ratios, for efficient and consistent drug layering.

Composition Dependency of the Flory-Huggins Interaction Parameter in Drug-Polymer Phase Behavior

An innovative strategy to address recent challenges in the oral administration of poorly soluble drugs is the formulation of amorphous solid dispersions (ASDs), where the drug is dissolved in a highly soluble carrier polymer. Therefore, special knowledge of the drug-polymer phase behavior is essential for an effective product and process design, accelerating the introduction of novel efficacious ASD products. Flory-Huggins theory can be applied to model solubility temperatures of crystalline drugs in carrier polymers over the drug fraction. However, predicted solubility temperatures lack accuracy in cases of strong drug/polymer interactions that are not represented in the Flory-Huggins lattice model. Within this study, a modeling strategy is proposed to improve the predictive power through an extension of the Flory-Huggins interaction parameter by a correlation with the drug fraction. Therefore, the composition dependency of the Flory-Huggins interaction parameter was evaluated experimentally for various drug-polymer formulations that cover a wide variety of drug and polymer characteristics regarding molecular weights, glass transition temperatures and melting temperatures, as well as drug-polymer interactions of different strengths and effects. The extended model was successfully approved for nine exemplary ASD formulations containing the drugs acetaminophen, itraconazole, and griseofulvine, as well as the following polymers: basic butylated methacrylate copolymer, Soluplus®, and vinylpyrrolidone/vinyl acetate copolymer. A high correlation between the predicted solubility temperatures and experimental and literature data was found, particularly at low drug fractions, since the model accounts for composition dependent drug-polymer interactions.