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In the present work molecular mobility and intermolecular interactions were evaluated as two distinct mechanisms for amorphous agomelatine (AGM) stabilization in the presence of pyrogenic silica. Specifically, amorphous AGM properties related to molecular mobility in terms of relaxation time were calculated based on the Kohlrausch–Williams–Watts (KWW) and Adam-Gibbs (AG) equations, while the kinetic fragility index was calculated based on temperature-modulated differential scanning calorimetry (TM-DSC). Results showed that independently of the approach followed (KWW or AG) AGM’s molecular mobility was reduced in the presence of silica (KWW calculated stretched relaxation time constant, τβ, was 83.61 and 44.78 for AGM and AGM/silica dispersions; respectively, while AG-based initial relaxation time, τ0, at storage temperatures 40–50 K below AGM’s Tg was increased from six to eight days in the presence of silica); while kinetic fragility index values for amorphous AGM were reduced from 116.05 to 110.24 in the presence of silica. Additionally, MD simulations verified experimentally via attenuated total reflectance (ATR) FTIR spectroscopy, revealed the presence of significant intermolecular interactions between AGM and silica which act as an additional mechanism for amorphous AGM stabilization.

A realistic molecular description of amorphous drug-polymer-plasticizer matrices, suitable for the preparation of amorphous solid dispersions (ASDs) with the aid of fusion-based techniques, was evaluated. Specifically, the incorporation of two model drugs (i.e. ibuprofen, IBU, and carbamazepine, CBZ) having substantially different thermal properties and glass forming ability, on the molecular representation of polyvinyl caprolactam–polyvinyl acetate–polyethylene glycol graft copolymer (SOL)/polyethylene glycol (PEG, working as a plasticizer) molecular and thermal properties were evaluated with the aid of classical molecular dynamics (MD) and docking simulations. Results showed good agreement between molecular modelling estimations and experimentally determined properties. Specifically, the computed Tg values that resulted from MD simulations for IBU-SOL/PEG and CBZ-SOL/PEG (53.8 and 54.2 °C, respectively) were in reasonable agreement with the corresponding values resulting from differential scanning calorimetry (DSC) measurements (49.8 and 50.1 °C), while both molecular modelling and experimental obtained results suggested miscibility among system components. Additionally, interactions between CBZ and SOL observed during MD simulations were verified by FTIR analysis, while MD simulations of the hydration process suggested strong molecular interactions between IBU-SOL and CBZ-SOL.

Nanocrystal formulations of the BCS class II agomelatine, were developed by wet media milling. The most suitable stabilizer was identified and effects of process and formulation variables on the nanocrystal size and ζ-potential were evaluated employing a Box-Behnken experimental design. The optimized nanosuspensions were dried and subsequently evaluated for redispersibility and physicochemical properties. Computational simulation of solid state properties was applied to rationalize crystal fracture. It was found that low viscosity hydroxypropylcellulose with sodium dodecyl sulfate is the most suitable stabilizer. Stabilizer concentration exerts a statistically significant effect on particle size, which depends on the mill's rotation speed. The milling process induces a polymorphic transition to form II, which could affect size reduction kinetics. The solidified nanosuspensions' redispersibility is deteriorating progressively with storage time, with only minor differences between drying methods, retaining enhanced dissolution rate. Crystal lattice simulations suggest high mechanical anisotropy of form I crystals, which could be an additional reason for fast particle size reduction prior to the polymorphic transformation. Wet media milling, combined with a suitable drying method, can be an efficient technique for the production of stable nanocrystals of agomelatine. Particle informatics methods can enhance our understanding of the mechanisms responsible for agomelatine's nanocomminution.

The correlation between glass forming ability (GFA) and several thermophysical or physicochemical properties of APIs with the formation and the physical stability of amorphous solid dispersions (ASDs) was evaluated in the present study. Eight poorly water-soluble APIs belonging in different GFA classes (i.e. a) GFA Class I: Carbamazepine, CBZ, b) GFA Class II: Agomelatine, AGO, Aprepitant, APT, Rivaroxaban, RIV, and c) GFA Class III: Indomethacin, IND, Pioglitazone, PIO, Piroxixam, PIR, and Simvastatin, SIM) were tested, in addition to six commonly used matrix-carriers (namely povidone, PVP, hydroxypropyl cellulose, HPC-SL, copovidone, coPVP, Soluplus®, SOL, and gelatin) in order to prepared ASDs via film casting approach. Results using polarized light microscopy (PLM) showed a similar drug crystallization tendency from ASDs independently of their GFA classification, glass stability or glass fragility. X-ray diffraction analysis verified the formation and the physical stability of ASD (independently of GFA class) when a suitable matrix-carrier was selected (i.e. SOL for AGO, RIV and SIM, PVP for APT, CBZ and IND, coPVP for PIO and gelatin for PIR). Further attempts to correlate some physicochemical properties (i.e. component's binding affinity and miscibility) with the formation and the crystallization tendency of the prepared ASDs showed no apparent correlation in regards to the different drug GFA classes. Finally, the evaluation of molecular interactions via FTIR analysis also failed to adequately distinguish the differences in regards to the formation and the physical stability of the prepared systems.

The present study evaluates the physical stability and intermolecular interactions of Rivaroxaban (RXB) amorphous solid dispersions (ASDs) in polymeric carriers via thermodynamic modelling and molecular simulations. Specifically, the Flory-Huggins (FH) lattice solution theory was used to construct thermodynamic phase diagrams of RXB ASDs in four commonly used polymeric carriers (i.e. copovidone, coPVP, povidone, PVP, Soluplus, SOL and hypromellose acetate succinate, HPMCAS), which were stored under 0%, 60% and 75% relative humidity (RH) conditions. In order to verify the phase boundaries predicted by FH modelling (i.e. truly amorphous zone, amorphous-amorphous demixing zones and amorphous-API recrystallization zones), samples of ASDs were examined via polarized light microscopy after storage for up to six months at various RH conditions. Results showed a good agreement between the theoretical and the experimental approaches (i.e. coPVP and PVP resulted in less physically-stable ASDs compared to SOL and HPMCAS) indicating that the proposed FH-based modelling may be a useful tool in predicting long-term physical stability in high humidity conditions. In addition, molecular dynamics (MD) simulations were employed in order to interpret the observed differences in physical stability. Results, which were verified via differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), suggested the formation of similar intermolecular interactions in all cases, indicating that the interaction with moisture water plays a more crucial role in ASD physical stability compared to the formation of intermolecular interactions between ASD components.

Wet media milling, coupled with spay drying, is a commonly proposed formulation strategy for the production and solidification of nanosuspensions in order to overcome the solubility barrier of BCS Class II substances. However, the application of mechanically and thermally intensive processes is not straightforward in the cases of ductile and/or low melting point substances that may additionally be susceptible to eutectic formation. Using ibuprofen (IBU) as a model drug with non-favorable mechanical and melting properties, we attempt to rationalize nanocrystal formulation and manufacturing in an integrated approach by implementing Quality by Design (QbD) methodology, particle informatics techniques and computationally assisted process design. Wet media milling was performed in the presence of different stabilizers and co-milling agents, and the nanosuspensions were solidified by spray-drying. The effects of key process parameters (bead diameter, milling time and rotational speed) and formulation variables (stabilizer type and drug/stabilizer ratio) on the critical quality attributes (CQAs), i.e., Z-average size, polydispersity index (PDI), &zeta, potential and redispersibility of spray-dried nanosuspensions were evaluated, while possible correlations between IBU free surface energy and stabilizer effectiveness were studied. The fracture mechanism and surface stabilization of IBU were investigated by computer simulation of the molecular interactions at the crystal lattice level. As a further step, process design accounting for mass-energy balances and predictive thermodynamic models were constructed to scale-up and optimize the design space. Contemplating several limitations, our multilevel approach offers insights on the mechanistic pathway applicable to the substances featuring thermosensitivity and eutectic tendency.

The present study evaluates the effect of several pharmaceutical plasticizers on the thermo-physical and physicochemical properties of partially hydrolyzed poly(vinyl alcohol) (PVA) used in fusion-based pharmaceutical formulation processes. Specifically, the effect of mannitol (MAN), sorbitol (SOR), sucrose (SUC), anhydrous citric acid (CA), triethyl citrate (TEC) and low-molecular weight polyethylene glycol (PEG400) on PVA’s melting properties, physical state and thermal degradation was evaluated via differential scanning calorimetry (DSC), powder X-ray diffractometry (pXRD) and thermo-gravimetric analysis (TGA). Results showed that the use of MAN, SOR, SUC and PEG400 led to the reduction of PVA’s melting onset temperature, while MAN, SUC, CA and SOR were amorphously dispersed within PVA’s matrix, and the addition of SUC and CA resulted in significant reduction of PVA’s crystallinity. TGA results showed the formation of thermally highly unstable PVA mixtures in the cases of CA and TEC (degradation started from ~150 °C and ~125 °C, respectively), while significant molecular interactions were identified by FTIR in the cases of PVA-MAN, PVA-SOR and PVA-SUC. Hot-stage polarized microscopy (HSM) revealed PVA’s melt miscibility only with MAN and SOR, while melt flow index (MFI) measurements showed that the use of MAN, SOR and PEG400 resulted in a significant improvement of PVA’s melt flow properties. Finally, MD simulations were in close agreement with the experimental observations, indicating that they can be considered as a promising tool for the theoretical modelling of such systems.

The present work describes the development of a novel formulation of amorphous agomelatine (AGM) that exhibits enhanced in vitro dissolution rate and bioavailability, as well as improved storage stability. AGM was loaded on a mixture of microcrystalline cellulose with a high specific surface area excipient, namely colloidal silicon dioxide, employing a wet granulation method, and the resultant AGM granules were subsequently formulated into immediate release film-coated tablets. Modulated temperature differential scanning calorimetry, hot-state light microscopy, powder X-ray diffraction, attenuated total reflectance FTIR, and micro-Raman spectroscopy revealed that the active pharmaceutical ingredient existed primarily in the amorphous state within the prepared formulations, with some crystals of polymorph I also present. Accelerated stability studies for up to 6 months in alu-alu blisters showed good physicochemical stability during storage. Finally, in vitro dissolution studies and clinical trials in healthy human volunteers showed a remarkable increase in the in vitro dissolution rate and a ∼1.5-fold increase in bioavailability, respectively, compared to the marketed product.