The Need for Restructuring the Disordered Science of Amorphous Drug Formulations

The alarming numbers of poorly soluble discovery compounds have centered the efforts towards finding strategies to improve the solubility. One of the attractive approaches to enhance solubility is via amorphization despite the stability issue associated with it. Although the number of amorphous-based research reports has increased tremendously after year 2000, little is known on the current research practice in designing amorphous formulation and how it has changed after the concept of solid dispersion was first introduced decades ago. In this review we try to answer the following questions: What model compounds and excipients have been used in amorphous-based research? How were these two components selected and prepared? What methods have been used to assess the performance of amorphous formulation? What methodology have evolved and/or been standardized since amorphous-based formulation was first introduced and to what extent have we embraced on new methods? Is the extent of research mirrored in the number of marketed amorphous drug products? We have summarized the history and evolution of amorphous formulation and discuss the current status of amorphous formulation-related research practice. We also explore the potential uses of old experimental methods and how they can be used in tandem with computational tools in designing amorphous formulation more efficiently than the traditional trial-and-error approach

Early drug development predictions of glass-forming ability and physical stability of drugs

The purpose of this study was to investigate if rapidly measured physical properties can predict glass-forming ability and glass stability of drug compounds. A series of 50 structurally diverse drug molecules were studied with respect to glass-forming ability and, for glass-formers (n = 24), the physical stability upon 1 month of storage was determined. Spray-drying and melt-cooling were used to produce the amorphous material and the solid state was analysed by Differential Scanning Calorimetry (DSC) and Powder X-ray Diffraction. Thermal properties and molecular weight (Mw) were used to develop predictive models of (i) glass-forming ability and (ii) physical stability. In total, the glass-forming ability was correctly predicted for 90% of the drugs from their Mw alone. As a rule of thumb, drugs with Mw greater than 300 g/mole are expected to be transformed to its amorphous state by using standard process technology. Glass transition temperature and Mw predicted the physical stability upon storage correctly for 78% of the glass-forming compounds. A strong sigmoidal relationship (R-2 of 0.96) was identified between crystallization temperature and stability. These findings have the potential to rationalize decisions schemes for utilizing and developing amorphous formulations, through early predictions of glass-forming ability from Mw and physical stability from simple DSC characterization

Physical stability of drugs after storage above and below the glass transition temperature: Relationship to glass-forming ability

A B S T R A C T Amorphous materials are inherently unstable and tend to crystallize upon storage. In this study, we investigated the extent to which the physical stability and inherent crystallization tendency of drugs are related to their glass-forming ability (GFA), the glass transition temperature (T g ) and thermodynamic factors. Differential scanning calorimetry was used to produce the amorphous state of 52 drugs [18 compounds crystallized upon heating (Class II) and 34 remained in the amorphous state (Class III)] and to perform in situ storage for the amorphous material for 12 h at temperatures 20 C above or below the T g . A computational model based on the support vector machine (SVM) algorithm was developed to predict the structure-property relationships. All drugs maintained their Class when stored at 20 C below the T g . Fourteen of the Class II compounds crystallized when stored above the T g whereas all except one of the Class III compounds remained amorphous. These results were only related to the glass-forming ability and no relationship to e.g. thermodynamic factors was found. The experimental data were used for computational modeling and a classification model was developed that correctly predicted the physical stability above the T g . The use of a large dataset revealed that molecular features related to aromaticity and p-p interactions reduce the inherent physical stability of amorphous drugs

Physical stability of drugs after storage above and below the glass transition temperature : Relationship to glass-forming ability

Amorphous materials are inherently unstable and tend to crystallize upon storage. In this study, we investigated the extent to which the physical stability and inherent crystallization tendency of drugs are related to their glass-forming ability (GFA), the glass transition temperature (T-g) and thermodynamic factors. Differential scanning calorimetry was used to produce the amorphous state of 52 drugs [ 18 compounds crystallized upon heating (Class II) and 34 remained in the amorphous state (Class III)] and to perform in situ storage for the amorphous material for 12 h at temperatures 20 degrees C above or below the T-g. A computational model based on the support vector machine (SVM) algorithm was developed to predict the structure-property relationships. All drugs maintained their Class when stored at 20 degrees C below the T-g. Fourteen of the Class II compounds crystallized when stored above the T-g whereas all except one of the Class III compounds remained amorphous. These results were only related to the glass-forming ability and no relationship to e. g. thermodynamic factors was found. The experimental data were used for computational modeling and a classification model was developed that correctly predicted the physical stability above the T-g. The use of a large dataset revealed that molecular features related to aromaticity and pi-pi interactions reduce the inherent physical stability of amorphous drugs

Physical stability of drugs after storage above and below the glass transition temperature : Relationship to glass-forming ability

Amorphous materials are inherently unstable and tend to crystallize upon storage. In this study, we investigated the extent to which the physical stability and inherent crystallization tendency of drugs are related to their glass-forming ability (GFA), the glass transition temperature (T-g) and thermodynamic factors. Differential scanning calorimetry was used to produce the amorphous state of 52 drugs [ 18 compounds crystallized upon heating (Class II) and 34 remained in the amorphous state (Class III)] and to perform in situ storage for the amorphous material for 12 h at temperatures 20 degrees C above or below the T-g. A computational model based on the support vector machine (SVM) algorithm was developed to predict the structure-property relationships. All drugs maintained their Class when stored at 20 degrees C below the T-g. Fourteen of the Class II compounds crystallized when stored above the T-g whereas all except one of the Class III compounds remained amorphous. These results were only related to the glass-forming ability and no relationship to e. g. thermodynamic factors was found. The experimental data were used for computational modeling and a classification model was developed that correctly predicted the physical stability above the T-g. The use of a large dataset revealed that molecular features related to aromaticity and pi-pi interactions reduce the inherent physical stability of amorphous drugs

A novel powder sample holder for determination of glass transition temperatures by DMA

The use of a new sample holder for dynamic mechanical analysis (DMA) as a means to characterise the Tg of powdered hydroxypropyl methyl cellulose (HPMC) has been investigated. A sample holder was constructed consisting of a rectangular stainless steel container and a lid engineered to fit exactly within the walls of the container when clamped within a TA instruments Q800 DMA in dual cantilever configuration. Physical mixtures of HPMC (E4M) and aluminium oxide powders were placed in the holder and subjected to oscillating strains (1 Hz, 10 Hz and 100 Hz) whilst heated at 3 degrees C/min. The storage and loss modulus signals showed a large reduction in the mechanical strength above 150 degrees C which was attributed to a glass transition. Optimal experimental parameters were determined using a design of experiment procedure and by analysing the frequency dependence of Tg in Arrhenius plots. The parameters were a clamping pressure of 62 kPa, a mass ratio of 0.2 HPMC in aluminium oxide, and a loading mass of either 120 mg or 180 mg. At 1 Hz, a Tg of 177+/-1.2 degrees C (n=6) for powdered HPMC was obtained. In conclusion, the new powder holder was capable of measuring the Tg of pharmaceutical powders and a simple optimization protocol was established, useful in further applications of the DMA powder holder

Formulation factors affecting foam properties during vacuum foam-drying

This paper explores how vacuum foam-drying of a protein is influenced by formulation parameters by investigating the foam structure, physical properties of the foam, and the stability of the protein. Recombinant human bile salt-stimulated lipase was used as a model of a protein drug. The stability of the lipase was evaluated through activity measurements. Two disaccharides (sucrose and trehalose), strongly tending to an amorphous form, were used as matrix formers, and the physical properties were assessed through residual water content, glass transition temperature, and crystalline state. Moreover, some formulations included surfactants with different sizes and structures of the head group. The alkyl chain length was kept constant to only investigate the impact of the surfactant head group, in the presence of the lipase, on the foamability and surface coverage of the lipase. The study demonstrated that the lipase allowed for a dry, solid foam with a foam overrun of up to 2600 %. The wall thickness of the dry, solid foam was estimated to be 20–50 µm. Clear differences between sucrose and trehalose as matrix former were identified. The lipase showed no tendency to lose activity because of the drying and rehydration, despite a proportion of the lipase covering the surfaces of the dry material. 'Correspondence Address: D. Tristan Osanlóo; RISE Research Institutes of Sweden, Stockholm, Box 5604, SE-114 86, Sweden; The authors would like to thank Swedish Orphan Biovitrum for providing the lipase and Croda Nordica AB for the delivery of the surfactants. Dr. Stefan Ulvenlund (ENZA Biotech AB) is gratefully acknowledged for the delivery of surfactants and valuable discussions. This research was funded by the Swedish Governmental Agency for Innovation Systems (VINNOVA) and was carried out within the competence center NextBioForm (grant number 2018-04730).</p

Computational predictions of glass-forming ability and crystallization tendency of drug molecules.

Amorphization is an attractive formulation technique for drugs suffering from poor aqueous solubility as a result of their high lattice energy. Computational models that can predict the material properties associated with amorphization, such as glass-forming ability (GFA) and crystallization behavior in the dry state, would be a time-saving, cost-effective, and material-sparing approach compared to traditional experimental procedures. This article presents predictive models of these properties developed using support vector machine (SVM) algorithm. The GFA and crystallization tendency were investigated by melt-quenching 131 drug molecules in situ using differential scanning calorimetry. The SVM algorithm was used to develop computational models based on calculated molecular descriptors. The analyses confirmed the previously suggested cutoff molecular weight (MW) of 300 for glass-formers, and also clarified the extent to which MW can be used to predict the GFA of compounds with MW < 300. The topological equivalent of Grav3_3D, which is related to molecular size and shape, was a better descriptor than MW for GFA; it was able to accurately predict 86% of the data set regardless of MW. The potential for crystallization was predicted using molecular descriptors reflecting Hückel pi atomic charges and the number of hydrogen bond acceptors. The models developed could be used in the early drug development stage to indicate whether amorphization would be a suitable formulation strategy for improving the dissolution and/or apparent solubility of poorly soluble compounds

Experimental and Computational Prediction of Glass Transition Temperature of Drugs

Glass transition temperature (<i>T</i>_g) is an important inherent property of an amorphous solid material which is usually determined experimentally. In this study, the relation between <i>T</i>_g and melting temperature (<i>T</i>_m) was evaluated using a data set of 71 structurally diverse druglike compounds. Further, in silico models for prediction of <i>T</i>_g were developed based on calculated molecular descriptors and linear (multilinear regression, partial least-squares, principal component regression) and nonlinear (neural network, support vector regression) modeling techniques. The models based on <i>T</i>_m predicted <i>T</i>_g with an RMSE of 19.5 K for the test set. Among the five computational models developed herein the support vector regression gave the best result with RMSE of 18.7 K for the test set using only four chemical descriptors. Hence, two different models that predict <i>T</i>_g of drug-like molecules with high accuracy were developed. If <i>T</i>_m is available, a simple linear regression can be used to predict <i>T</i>_g. However, the results also suggest that support vector regression and calculated molecular descriptors can predict <i>T</i>_g with equal accuracy, already before compound synthesis