Are traditional small-scale screening methods reliable to predict pharmaceutical spray drying?

Miniaturized screening and performance prediction of tailored subcutaneous extended-release formulations for preclinical in vivo studies

Microencapsulation of active pharmaceutical ingredients (APIs) for preparation of long acting injectable (LAI) formulations is an auspicious technique to enable preclinical characterization of a broad variety of APIs, ideally independent of their physicochemical and pharmacokinetic (PK) characteristics. During early API discovery, tunable LAI formulations may enable pharmacological proof-of-concept for the given variety of candidates by tailoring the level of plasma exposure over the duration of various timespans. Although numerous reports on small scale preparation methods for LAIs utilizing copolymers of lactic and glycolic acid (PLGA) and polymers of lactic acid (PLA) highlight their potential, application in formulation screening and use in preclinical in vivo studies is yet very limited. Transfer from downscale formulation preparation to in vivo experiments is hampered in early preclinical API screening by the large number of API candidates with simultaneously very limited available amount in the lower sub-gram scale, lack of formulation stability and deficient tunability of sustained release. We hereby present a novel comprehensive platform tool for tailored extended-release formulations, aiming to support a variety of preclinical in vivo experiments with ranging required plasma exposure levels and timespans. A novel small-scale spray drying process was successfully implemented by using an air brush based instrument for preparation of PLGA and PLA based formulations. Using Design of Experiments (DoE), required API amount of 250 mg was demonstrated to suffice for identification of dominant polymer characteristics with largest impact on sustained release capability for an individual API. BI-3231, a hydrophilic and weakly acidic small compound with good water solubility and permeability, but low metabolic stability, was used as an exemplary model for one of the many candidates during API discovery. Furthermore, an in vitro to in vivo correlation (IVIVC) of API release rate was established in mice, which enabled the prediction of in vivo plasma concentration plateaus after single subcutaneous injection, using only in vitro dissolution profiles of screened formulations. By tailoring LAI formulations and their doses for acute and sub-chronic preclinical experiments, we exemplary demonstrate the practical use for BI-3231. Pharmacological proof-of-concept could be enabled whilst circumventing the need of multiple administration as result of extensive hepatic metabolism and simultaneously superseding numerous in vivo experiments for formulation tailoring.

Densifying Co-Precipitated Amorphous Dispersions to Achieve Improved Bulk Powder Properties

PURPOSE

Precipitation of amorphous solid dispersions has gained traction in the pharmaceutical industry given its application to pharmaceuticals with varying physicochemical properties. Although preparing co-precipitated amorphous dispersions (cPAD) in high-shear rotor-stator devices allows for controlled shear conditions during precipitation, such aggressive mixing environments can result in materials with low bulk density and poor flowability. This work investigated annealing cPAD after precipitation by washing with heated anti-solvent to improve bulk powder properties required for downstream drug product processing.

METHODS

Co-precipitation dispersions were prepared by precipitation into pH-modified aqueous anti-solvent. Amorphous dispersions were washed with heated anti-solvent and assessed for bulk density, flowability, and dissolution behavior relative to both cPAD produced without a heated wash and spray dried intermediate.

RESULTS

Washing cPAD with a heated anti-solvent resulted in an improvement in flowability and increased bulk density. The mechanism of densification was ascribed to annealing over the wetted T_g of the material, which lead to collapse of the porous co-precipitate structure into densified granules without causing crystallization. In contrast, an alternative approach to increase bulk density by precipitating the ASD using low shear conditions showed evidence of crystallinity. The dissolution rate of the densified cPAD granules was lower than that of the low-bulk density dispersions, although both samples reached concentrations equivalent to that of the spray dried intermediate after 90 min dissolution.

CONCLUSIONS

Hot wash densification was a tenable route to produce co-precipitated amorphous dispersions with improved properties for downstream processing compared to non-densified powders.

The underestimated contribution of the solvent to the phase behavior of highly drug loaded amorphous solid dispersions

In spite of the fact that spray drying is widely applied for the formulation of amorphous solid dispersions (ASDs), the influence of the solvent on the physical properties of the ASDs is still not completely understood. Therefore, the impact of organic solvents on the kinetic stabilization of drug components in a polymer matrix prepared by either film casting or spray drying was investigated. One polymer, PVPVA 64, together with one of four poorly water soluble drugs, naproxen, indomethacin, fenofibrate or diazepam, were film casted and spray dried using either methanol, ethanol, isopropanol, acetonitrile, acetone, dichloromethane or ethyl acetate. For every combination, the highest drug loading that could be formulated as a single amorphous phase was established. The solvent determined the maximum amount of drug that could be kinetically trapped in the polymer matrix and thereby the extent of kinetic stabilization. These maximum drug loadings were compared to the thermodynamic solubilities of the drugs in the seven solvents. Generally, there was no relation between the thermodynamic solubility of a drug and its highest drug loading attained using the same solvent. Hence, the contribution of the solvent to the generation of a supersaturated state should not be underestimated.

Hierarchical Particle Approach for Co-Precipitated Amorphous Solid Dispersions for Use in Preclinical In Vivo Studies

Amorphous solid dispersions (ASD) have become a well-established strategy to improve exposure for compounds with insufficient aqueous solubility. Of methods to generate ASDs, spray drying is a leading route due to its relative simplicity, availability of equipment, and commercial scale capacity. However, the broader industry adoption of spray drying has revealed potential limitations, including the inability to process compounds with low solubility in volatile solvents, inconsistent molecular uniformity of spray dried amorphous dispersions, variable physical properties across batches and scales, and challenges containing potent compounds. In contrast, generating ASDs via co-precipitation to yield co-precipitated amorphous dispersions (cPAD) offers solutions to many of those challenges and has been shown to achieve ASDs comparable to those manufactured via spray drying. This manuscript applies co-precipitation for early safety studies, developing a streamlined process to achieve material suitable for dosing as a suspension in conventional toxicity studies. Development targets involved achieving a rapid, safely contained process for generating ASDs with high recovery yields. Furthermore, a hierarchical particle approach was used to generate composite particles where the cPAD material is incorporated in a matrix of water-soluble excipients to allow for rapid re-dispersibility in the safety study vehicle to achieve a uniform suspension for consistent dosing. Adopting such an approach yielded a co-precipitated amorphous dispersion with comparable stability, thermal properties, and in vivo pharmacokinetics to spray dried amorphous materials of the same composition.

Engineering Advances in Spray Drying for Pharmaceuticals

Spray drying is a versatile technology that has been applied widely in the chemical, food, and, most recently, pharmaceutical industries. This review focuses on engineering advances and the most significant applications of spray drying for pharmaceuticals. An in-depth view of the process and its use is provided for amorphous solid dispersions, a major, growing drug-delivery approach. Enhanced understanding of the relationship of spray-drying process parameters to final product quality attributes has made robust product development possible to address a wide range of pharmaceutical problem statements. Formulation and process optimization have leveraged the knowledge gained as the technology has matured, enabling improved process development from early feasibility screening through commercial applications. Spray drying's use for approved small-molecule oral products is highlighted, as are emerging applications specific to delivery of biologics and non-oral delivery of dry powders. Based on the changing landscape of the industry, significant future opportunities exist for pharmaceutical spray drying.

Analytical and Computational Methods for the Determination of Drug-Polymer Solubility and Miscibility

In the pharmaceutical industry, poorly water-soluble drugs require enabling technologies to increase apparent solubility in the biological environment. Amorphous solid dispersion (ASD) has emerged as an attractive strategy that has been used to market more than 20 oral pharmaceutical products. The amorphous form is inherently unstable and exhibits phase separation and crystallization during shelf life storage. Polymers stabilize the amorphous drug by antiplasticization, reducing molecular mobility, reducing chemical potential of drug, and increasing glass transition temperature in ASD. Here, drug-polymer miscibility is an important contributor to the physical stability of ASDs. The current Review discusses the basics of drug-polymer interactions with the major focus on the methods for the evaluation of solubility and miscibility of the drug in the polymer. Methods for the evaluation of drug-polymer solubility and miscibility have been classified as thermal, spectroscopic, microscopic, solid-liquid equilibrium-based, rheological, and computational methods. Thermal methods have been commonly used to determine the solubility of the drug in the polymer, while other methods provide qualitative information about drug-polymer miscibility. Despite advancements, the majority of these methods are still inadequate to provide the value of drug-polymer miscibility at room temperature. There is still a need for methods that can accurately determine drug-polymer miscibility at pharmaceutically relevant temperatures.

Solvent-Casted Films to Assist Polymer Selection for Amorphous Solid Dispersions During Preclinical Studies: In-vitro and In-vivo Exploration

PURPOSE

The use of two solvent-casted film methods to select optimal polymer compositions for amorphous solid dispersions prepared to support preclinical pharmacokinetic and toxicology studies is described.

METHODS

Evaporation of solvent from cover slips by using nitrogen flow, and solvent removal from vials by using rotary evaporation were employed. The films prepared on cover slips were evaluated under the microscope to determine crystallinity. The methods were validated by scaling up corresponding SDDs, evaluating SDD's dissolution, and comparing those results to the dissolution of drug-polymer films. Subsequently, SDD suspensions were prepared and dosed orally to rats to determine pharmacokinetic parameters. This was done by using three compounds from our pipeline and evaluating multiple polymers.

RESULTS

The dissolution of generated films showed good agreement with the dissolution of spray dried dispersions when the films were fully amorphous (Compound A and B). In contrast, there was disagreement between film and SDD dissolution when the films had crystallized (Compound C). The in vivo exposure results indicated that the polymer choice based on the film screening methods would have been accurate for drug-polymer films that were amorphous (Compound A and B). Two additional case studies (Compound D and E) are presented, showing good agreement between in vivo and in vitro results.

CONCLUSION

This study established the ability of two film casting screening methods to predict the in vitro and in vivo performance of corresponding SDDs, provided that the films are fully amorphous.