Rapid assessment of homogeneity and stability of amorphous solid dispersions by atomic force microscopy--from bench to batch.

PURPOSE: To verify the robustness and fundamental value of Atomic Force Microscopy (AFM) and AFM-based assays to rapidly examine the molecular homogeneity and physical stability of amorphous solid dispersions on Hot-Melt-Extrudates. METHODS: Amorphous solid dispersions were prepared with a Hot-Melt Extruder (HME) and profiled by Raman Microscopy and AFM following a sequential analytical routine (Multi-Scale-Imaging-of-Miscibiliy (MIMix)). Extrudates were analyzed before and after incubation at elevated temperature and humidity. The data were compared with published results as collected on miniaturized melt models. The value of molecular phase separation rates for long term stability prediction was assessed. RESULTS: Data recorded on the extrudates are consistent with those published, and they can be compared side by side. Such direct data comparisons allow the identification of possible sources of extrudate heterogeneities. The surface roughness analysis of fracture-exposed interfaces is a novel quantitative way to trace on the nanometer scale the efficiencies of differently conducted HME-processes. Molecular phase separation rates are shown to be relevant for long term stability predictions. CONCLUSIONS: The AFM-based assessment of API:excipient combinations is a robust method to rapidly identify miscible and stable solid dispersions in a routine manner. It provides a novel analytical tool for the optimization of HME processes.

Atomic force microscopy-based screening of drug-excipient miscibility and stability of solid dispersions.

PURPOSE: Development of a method to assess the drug/polymer miscibility and stability of solid dispersions using a melt-based mixing method. METHODS: Amorphous fractured films are prepared and characterized with Raman Microscopy in combination with Atomic Force Microscopy to discriminate between homogenously and heterogeneously mixed drug/polymer combinations. The homogenous combinations are analyzed further for physical stability under stress conditions, such as increased humidity or temperature. RESULTS: Combinations that have the potential to form a molecular disperse mixture are identified. Their potential to phase separate is determined through imaging at molecular length scales, which results in short observation time. De-mixing is quantified by phase separation analysis, and the drug/polymer combinations are ranked to identify the most stable combinations. CONCLUSIONS: The presented results demonstrate that drug/polymer miscibility and stability of solid dispersions, with many mechanistic details, can be analyzed with Atomic Force Microscopy. The assay allows to identify well-miscible and stable combinations within hours or a few days.

A Miniaturized Extruder to Prototype Amorphous Solid Dispersions: Selection of Plasticizers for Hot Melt Extrusion.

Hot-melt extrusion is an option to fabricate amorphous solid dispersions and to enhance oral bioavailability of poorly soluble compounds. The selection of suitable polymer carriers and processing aids determines the dissolution, homogeneity and stability performance of this solid dosage form. A miniaturized extrusion device (MinEx) was developed and Hypromellose acetate succinate type L (HPMCAS-L) based extrudates containing the model drugs neurokinin-1 (NK1) and cholesterylester transfer protein (CETP) were manufactured, plasticizers were added and their impact on dissolution and solid-state properties were assessed. Similar mixtures were manufactured with a lab-scale extruder, for face to face comparison. The properties of MinEx extrudates widely translated to those manufactured with a lab-scale extruder. Plasticizers, Polyethyleneglycol 4000 (PEG4000) and Poloxamer 188, were homogenously distributed but decreased the storage stability of the extrudates. Stearic acid was found condensed in ultrathin nanoplatelets which did not impact the storage stability of the system. Depending on their distribution and physicochemical properties, plasticizers can modulate storage stability and dissolution performance of extrudates. MinEx is a valuable prototyping-screening method and enables rational selection of plasticizers in a time and material sparing manner. In eight out of eight cases the properties of the extrudates translated to products manufactured in lab-scale extrusion trials.

Miniaturized X-ray powder diffraction assay (MixRay) for quantitative kinetic analysis of solvent-mediated phase transformations in pharmaceutics.

Many pharmaceutical compounds exhibit polymorphism, which may result in solvent-mediated phase transformations. Since the polymorphic form has an essential influence on physicochemical characteristics such as solubility or dissolution rate, it is crucial to know the exact polymorphic composition of a drug throughout pharmaceutical development. This study addressed the need to perform quantitative X-ray analysis of polymorphic mixtures on a 96-well scale (MixRay). A calibration of polymorphic mixtures (anhydrate and hydrate) was performed with three model drugs, caffeine, piroxicam, and testosterone, and linear correlations were obtained for all compounds. The MixRay approach for piroxicam was applied to a solubility and residual solid screening assay (SORESOS) to quantify the amount of hydrate and anhydrate corresponding to kinetic bulk concentrations. Changes in these drug concentrations correlated well with the kinetic changes in the residual solid. The influence of excipients on the solid state and kinetic concentrations of piroxicam was also studied. Excipients strongly affected polymorphic transformation kinetics of piroxicam and concentrations after 24h depended on the excipient used. The new calibration X-ray method combined with bulk concentration analysis provides a valuable tool for both pharmaceutical profiling and early formulation development.

Biomimetic nucleation and growth of CaCO3 in hydrogels incorporating carboxylate groups.

Poly-acrylamide hydrogels were modified by copolymerization with acrylic acid and used as growth medium for CaCO3 in a double-diffusion arrangement. The carboxylate functionalities in the gel network facilitate the nucleation of a multitude of small crystallites of vaterite and calcite, which are temporarily stabilized even while supersaturation is increasing within the hydrogel. After an extended induction period the rapid spherulitic growth of calcite crystals along their c-axis is observed yielding spheres with diameters exceeding 300 microm. In the center of those aggregates disordered, porous regions can be identified as starting point of this rapid crystallization. The results are compared to previous studies on native poly-acrylamide hydrogels and networks modified with -SO(3)H functional groups. The mineralization mechanism is significantly altered by specific interactions between the -COOH functionalized network and the evolving mineral phase.

Miniaturized assay for solubility and residual solid screening (SORESOS) in early drug development.

PURPOSE: The aim was to develop a miniaturized method for solubility and residual solid screening of drug compounds in aqueous and non-aqueous vehicles in early drug development. METHODS: Different crystal modifications of caffeine, carbamazepine, and piroxicam were added into 96-well filter plates and solubility was determined in 100 microl of 17 pharmaceutical vehicles. After filtration, drug concentration was determined by Ultra Performance Liquid Chromatography (UPLC). Residual solid drug in the filter plates was analyzed by high-throughput (HT) transmission X-ray Powder Diffraction (XRPD). RESULTS: HT XRPD analysis revealed solid form conversions of all compounds during solubility determination, e.g., formation of hydrates in aqueous vehicles (caffeine, carbamazepine, piroxicam) or conversion of a metastable crystal form to the stable form (caffeine). Drug solubility was strongly dependent on the crystal modifications formed during the solubility assay. CONCLUSIONS: The new assay allows the simultaneous, small scale screening of drug solubility in various pharmaceutical vehicles and identification of changes in solid form. It is useful for the identification of formulations and formulation options in non-clinical and clinical development.

Morphogenetic control of calcite crystal growth in sulfonic acid based hydrogels.

In this paper the mineralization of CaCO(3) in various hydrogel matrices is presented. Sulfonic acid based hydrogels were prepared by introduction of sulfonate-containing monomers into a polyacrylamide network. The sulfonate content of polyacrylamide-co-vinylsulfonate and polyacrylamide-co-allylsulfonate decreases during elution of the copolymers in demineralized water, indicating insufficient linking of the sulfonate-bearing monomers within the hydrogel. In contrast to this, acrylamidomethylpropanesulfonate (AMPS) effectively copolymerizes with acrylamide (AAm) monomers. To study the influence of spatial arrangement of ionic functional groups within hydrogel networks on the mineralization of CaCO(3), AMPS copolymers with different degrees of AMPS cross-linking were synthesized. For the mineralization experiments the copolymers were placed into a double-diffusion arrangement. Calcite as the thermodynamically stable modification of CaCO(3) was obtained with a particular morphology. The pseudocubic habitus resembles aggregates obtained by mineralization in pure polyacrylamide. However, closer examination of the aggregates by scanning electron microscopy (SEM) shows that the crystal growth in the AMPS copolymers is different from that observed in polyacrylamide. Whereas the morphology of the calcite aggregates could be fine-tuned by using copolymers with different sulfonate content, the spatial distribution of the ionic functional groups alters the course of crystallization. Calcium ions are locally accumulated due to the heterogeneous distribution of functional sulfonate groups within the copolymer network. Thereby the nucleation of calcite is triggered, resulting in enhanced mineralization.