Dissolution Behavior of Weakly Basic Pharmaceuticals from Amorphous Dispersions Stabilized by a Poly(dimethylaminoethyl Methacrylate) Copolymer

Poly(vinylpyridine-co-vinylpyridine N-oxide) Excipients Mediate Rapid Dissolution and Sustained Supersaturation of Posaconazole Amorphous Solid Dispersions

The chemical structure of excipients molecularly mixed in an amorphous solid dispersion (ASD) has a significant impact on properties of the ASD including dissolution behavior, physical stability, and bioavailability. Polymers used in ASDs require a balance between hydrophobic and hydrophilic functionalities to ensure rapid dissolution of the amorphous dispersion as well as sustained supersaturation of the drug in solution. This work demonstrates the use of postpolymerization functionalization of poly(vinylpyridine) excipients to elucidate the impact of polymer properties on the dissolution behavior of amorphous dispersions containing posaconazole. It was found that N-oxidation of pyridine functionalities increased the solubility of poly(vinylpyridine) derivatives in neutral aqueous conditions and allowed for nanoparticle formation which supplied posaconazole into solution at concentrations exceeding those achieved by more conventional excipients such as hydroxypropyl methylcellulose acetate succinate (HPMCAS) or Eudragit E PO. By leveraging these functional modifications of the parent poly(vinylpyridine) excipient to increase polymer hydrophilicity and minimize the effect of polymer on pH, a new polymeric excipient was optimized for rapid dissolution and supersaturation maintenance for a model compound.

Drug Aggregation of Sparingly-Soluble Ionizable Drugs: Molecular Dynamics Simulations of Papaverine and Prostaglandin F2α

Aggregation in aqueous solution can have important implications on both the in vivo exposure of a drug and its pharmaceutical manufacturability. However, the drug aggregates formed can be very small and, thus, difficult to interrogate experimentally. On the other hand, at higher supersaturations where larger aggregates are supported, the chemical system is inherently metastable and therefore likewise challenging to study from an experimental standpoint. Understanding aggregation behavior is further complicated in the case of ionizable drugs where, unlike neutral compounds, there can be uncertainty in the kinds of drug molecules (i.e., charged, neutral, or both) that become incorporated into various clusters, particularly at pH values near the pKa. In this paper, we apply physics-based all-atom molecular dynamics (MD) simulations to study aggregation in the weakly basic drug papaverine and in the weakly acidic drug prostaglandin F2α. We employ in silico tools to construct simulation workflows and comprehensive cluster analysis protocols to elucidate the size distributions and dynamics of the drug aggregates formed at both an experimentally relevant concentration and at high supersaturation. We build on a previously published treatment [Solubility of sparingly soluble ionizable drugs. Adv. Drug Deliv. Rev. 2007, 59, 568-590, DOI: 10.1016/j.addr.2007.05.008] to translate the predicted aggregate distributions of each ionized drug into corresponding pH-solubility curves that can be compared directly to experiment. Our findings show that the assumption of a single predominant (charged) aggregate can be misleading in interpreting experimental pH-solubility curves, as it does not adequately reflect the rich diversity revealed in our simulations. Beyond not accounting for the distribution of ionized drug-containing clusters actually observed in solution, for both drugs we find evidence that neutral drug molecules can also participate in the aggregation phenomena. Notably, we observe that many drug molecules remain as free monomers in solution even under simulated conditions designed to mimic those where there is significant deviation of the experimental pH-solubility curve from the Henderson-Hasselbalch (H-H) equation, often taken to be a clear signpost of drug aggregation.

Advances in the development of amorphous solid dispersions: The role of polymeric carriers

Amorphous solid dispersion (ASD) is one of the most effective approaches for delivering poorly soluble drugs. In ASDs, polymeric materials serve as the carriers in which the drugs are dispersed at the molecular level. To prepare the solid dispersions, there are many polymers with various physicochemical and thermochemical characteristics available for use in ASD formulations. Polymer selection is of great importance because it influences the stability, solubility and dissolution rates, manufacturing process, and bioavailability of the ASD. This review article provides a comprehensive overview of ASDs from the perspectives of physicochemical characteristics of polymers, formulation designs and preparation methods. Furthermore, considerations of safety and regulatory requirements along with the studies recommended for characterizing and evaluating polymeric carriers are briefly discussed.

Fed- and Fasted-State Performance of Pretomanid Amorphous Solid Dispersions Formulated with an Enteric Polymer

Weakly acid polymers with pH-responsive solubility are being used with increasing frequency in amorphous solid dispersion (ASD) formulations of drugs with low aqueous solubility. However, drug release and crystallization in a pH environment where the polymer is insoluble are not well understood. The aim of the current study was to develop ASD formulations optimized for release and supersaturation longevity of a rapidly crystallizing drug, pretomanid (PTM), and to evaluate a subset of these formulations in vivo. Following screening of several polymers for their ability to inhibit crystallization, hypromellose acetate succinate HF grade (HPMCAS-HF; HF) was selected to prepare PTM ASDs. In vitro release studies were conducted in simulated fasted- and fed-state media. Drug crystallization in ASDs following exposure to dissolution media was evaluated by powder X-ray diffraction, scanning electron microscopy, and polarized light microscopy. In vivo oral pharmacokinetic evaluation was conducted in male cynomolgus monkeys (n = 4) given 30 mg PTM under both fasted and fed conditions in a crossover design. Three HPMCAS-based ASDs of PTM were selected for fasted-state animal studies based on their in vitro release performance. Enhanced bioavailability was observed for each of these formulations relative to the reference product that contained crystalline drug. The 20% drug loading PTM-HF ASD gave the best performance in the fasted state, with subsequent dosing in the fed state. Interestingly, while food improved drug absorption of the crystalline reference product, the exposure of the ASD formulation was negatively impacted. The failure of the HPMCAS-HF ASD to enhance absorption in the fed state was hypothesized to result from poor release in the reduced pH intestinal environment resulting from the fed state. In vitro experiments confirmed a reduced release rate under lower pH conditions, which was attributed to reduced polymer solubility and an enhanced crystallization tendency of the drug. These findings emphasize the limitations of in vitro assessment of ASD performance using standardized media conditions. Future studies are needed for improved understanding of food effects on ASD release and how this variability can be captured by in vitro testing methodologies for better prediction of in vivo outcomes, in particular for ASDs formulated with enteric polymers.

A Comparison of Spray-Drying and Co-Precipitation for the Generation of Amorphous Solid Dispersions (ASDs) of Hydrochlorothiazide and Simvastatin

Co-processing of APIs, the practice of creating multi-component APIs directly in chemical processing facilities used to make drug substance, is gaining increased attention with a view to streamlining manufacturing, improving supply chain robustness and accessing enhanced product attributes in terms of stability and bioavailability. Direct co-precipitation of amorphous solid dispersions (ASDs) at the final step of chemical processing is one such example of co-processing. The purpose of this work was to investigate the application of different advanced solvent-based processing techniques - direct co-precipitation (CP) and the benchmark well-established spray-drying (SD) process - to the production of ASDs comprised of a drug with a high T_g (hydrochlorothiazide, HCTZ) or a low T_g (simvastatin, SIM) molecularly dispersed in a PVP/VA 64 or Soluplus® matrix. ASDs of the same composition were manufactured by the two different methods and were characterised using powder X-ray diffraction (PXRD), modulated differential scanning calorimetry (mDSC), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM). Both methods produced ASDs that were PXRD amorphous, with some differences, depending on the process used, in glass transition temperature and particle size distribution. Irrespective of manufacturing method used, all ASDs remained PXRD amorphous when subjected to high relative humidity conditions (75% RH, 25°C) for four weeks, although changes in the colour and physical characteristics were observed on storage for spray-dried systems with SIM and PVP/VA 64 copolymer. The particle morphology differed for co-precipitated compared to spray dried systems, with powder generated by the former process being comprised of more irregularly shaped particles of larger particle size when compared to the equivalent spray-dried systems which may enable more streamlined drug product processes to be used for CP materials. These differences may have implications in downstream drug product processing. A limitation identified when applying the solvent/anti-solvent co-precipitation method to SIM was the high antisolvent to solvent ratios required to effect the precipitation process. Thus, while similar outcomes may arise for both co-precipitation and spray drying processes in terms of ASD critical quality attributes, practical implications of applying the co-precipitation method and downstream processability of the resulting ASDs should be considered when choosing one solvent-based ASD production process over another.

Microfluidic Particle Engineering of Hydrophobic Drug with Eudragit E100─Bridging the Amorphous and Crystalline Gap

Co-processing active pharmaceutical ingredients (APIs) with excipients is a promising particle engineering technique to improve the API physical properties, which can lead to more robust downstream drug product manufacturing and improved drug product attributes. Excipients provide control over critical API attributes like particle size and solid-state outcomes. Eudragit E100 is a widely used polymeric excipient to modulate drug release. Being cationic, it is primarily employed as a precipitation inhibitor to stabilize amorphous solid dispersions. In this work, we demonstrate how co-processing of E100 with naproxen (NPX) (a model hydrophobic API) into monodisperse emulsions via droplet microfluidics followed by solidification via solvent evaporation allows the facile fabrication of compact, monodisperse, and spherical particles with an expanded range of solid-state outcomes spanning from amorphous to crystalline forms. Low E100 concentrations (≤26% w/w) yield crystalline microparticles with a stable NPX polymorph distributed uniformly across the matrix at a high drug loading (∼89% w/w). Structurally, E100 incorporation reduces the size of primary particles comprising the co-processed microparticles in comparison to neat API microparticles made using the same technique and the as-received API powder. This reduction in primary particle size translates into an increased internal porosity of the co-processed microparticles, with specific surface area and pore volume ∼9 times higher than the neat API microparticles. These E100-enabled structural modifications result in faster drug release in acidic media compared to neat API microparticles. Additionally, E100-NPX microparticles have a significantly improved flowability compared to neat API microparticles and as-received API powder. Overall, this study demonstrates a facile microfluidics-based co-processing method that broadly expands the range of solid-state outcomes obtainable with E100 as an excipient, with multiscale control over the key attributes and performance of hydrophobic API-laden microparticles.