Characterization of Amorphous and Co-Amorphous Simvastatin Formulations Prepared by Spray Drying

Evidence of Strong Guest-Host Interactions in Simvastatin Loaded in Mesoporous Silica MCM-41

A rational design of drug delivery systems requires in-depth knowledge not only of the drug itself, in terms of physical state and molecular mobility, but also of how it is distributed among a carrier and its interactions with the host matrix. In this context, this work reports the behavior of simvastatin (SIM) loaded in mesoporous silica MCM-41 matrix (average pore diameter ~3.5 nm) accessed by a set of experimental techniques, evidencing that it exists in an amorphous state (X-ray diffraction, ssNMR, ATR-FTIR, and DSC). The most significant fraction of SIM molecules corresponds to a high thermal resistant population, as shown by thermogravimetry, and which interacts strongly with the MCM silanol groups, as revealed by ATR-FTIR analysis. These findings are supported by Molecular Dynamics (MD) simulations predicting that SIM molecules anchor to the inner pore wall through multiple hydrogen bonds. This anchored molecular fraction lacks a calorimetric and dielectric signature corresponding to a dynamically rigid population. Furthermore, differential scanning calorimetry showed a weak glass transition that is shifted to lower temperatures compared to bulk amorphous SIM. This accelerated molecular population is coherent with an in-pore fraction of molecules distinct from bulklike SIM, as highlighted by MD simulations. MCM-41 loading proved to be a suitable strategy for a long-term stabilization (at least three years) of simvastatin in the amorphous form, whose unanchored population releases at a much higher rate compared to the crystalline drug dissolution. Oppositely, the surface-attached molecules are kept entrapped inside pores even after long-term release assays.

Effect of sodium lauryl sulfate-mediated gelation on the suppressed dissolution of crystalline lurasidone hydrochloride and a strategy to mitigate the gelation

In dissolution test, the surfactant sodium lauryl sulfate (SLS) is usually added to increase the dissolution of insoluble drugs and achieve the sink condition. However, the current study found that 0.1 % SLS would significantly decrease the dissolution of crystalline lurasidone hydrochloride (LH, a BCS Ⅱ drug). The aim of this study was to clarify the mechanism of this unexpected phenomenon and explore a strategy for mitigating the negative effect of SLS on the dissolution of LH. Sample characterizations (such as PLM, DSC, PXRD, IR and NMR) confirmed that the insoluble single-phase amorphous LH-SLS complex (with a single T_g at 35.2 °C) formed during dissolution in 0.1 % SLS aqueous solution via electrostatic interaction, tetrel bond interaction, and hydrophobic effect. Due to the plasticization effect of water, the transition of amorphous LH-SLS from its glassy state to viscous supercooled liquid state led to the gel formation, and suppressd the dissolution of LH. Meanwhile, the solubility curve of LH in SLS aqueous solution at various concentrations exhibited an unusual V-shaped feature, with the CMC value of SLS serving as the inflection point, since the gel degree was attenuated due to the micelle solubilization of SLS. Additionally, an innovative strategy was developed to alleviate the inhibiting effect of SLS on LH dissolution based on the potential competitive interactions. This study not only enriches the internal mechanism of surfactant-inhibited drug dissolution but also informs an effective strategy to mitigate the gelation.

Benchmarking the Solubility Enhancement and Storage Stability of Amorphous Drug–Polyelectrolyte Nanoplex against Co-Amorphous Formulation of the Same Drug

Amorphization, typically in the form of amorphous solid dispersion (ASD), represents a well-established solubility enhancement strategy for poorly soluble drugs. Recently, two amorphous drug formulations, i.e., the amorphous drug–polyelectrolyte nanoparticle complex (nanoplex) and co-amorphous system, have emerged as promising alternatives to circumvent the issues faced by ASD (i.e., large dosage requirement, high hygroscopicity). In the present work, the nanoplex was benchmarked against the co-amorphous system in terms of the preparation efficiency, drug payload, thermal stability, dissolution rate, supersaturation generation, and accelerated storage stability. Weakly acidic curcumin (CUR) and weakly basic ciprofloxacin (CIP) were used as the model poorly soluble drugs. The CUR and CIP nanoplexes were prepared using chitosan and sodium dextran sulfate as the polyelectrolytes, respectively. The co-amorphous CUR and CIP were prepared using tannic acid and tryptophan as the co-formers, respectively. The benchmarking results showed that the amorphous drug nanoplex performed as well as, if not better than, the co-amorphous system depending on the drug in question and the aspects being compared. The present work successfully established the nanoplex as an equally viable amorphous drug formulation as the more widely studied co-amorphous system to potentially serve as an alternative to ASD.

Characterization of excipients to improve pharmaceutical properties of sirolimus in the supercritical anti-solvent fluidized process

Enhanced drug release and bioavailability of poorly soluble active pharmaceutical ingredient (API) can be achieved via a fluidized bed coating integrated with supercritical anti-solvent (SAS-FB) - a process of precipitating drug particles onto carrier granules. However, in the absence of excipients, SAS-FB often results in crystalline of the API on the surface of carriers, limiting the improvement of pharmaceutical properties. Co-processing with excipients is considered an effective approach to improve drug release in the SAS-FB process. Our study used sirolimus, an immune suppressive agent, as the model API to characterize excipients for their effect on pharmaceutical properties in the SAS-FB process. We show that co-precipitation of excipients and sirolumus impacts on carrier specific surface area and drug yield. Among the tested excipients, formulation containing polyvinylpyrrolidone K30 achieved the highest drug yield. Importantly, compared with Rapamune® tablet, our optimized formulation displayed a superior in vivo oral bioavailability by 3.05-fold in Sprague-Dawley rats and 3.99-fold in beagle dogs. A series of characterization of the processed API was performed to understand the mechanism by which excipients contributed to drug dissolution properties. Our study provides a useful guidance for the use of excipients in the SAS-FB technology to improve pharmaceutical properties of sirolimus and other poorly soluble drugs.

Combinations of Freeze-Dried Amorphous Vardenafil Hydrochloride with Saccharides as a Way to Enhance Dissolution Rate and Permeability

To improve physicochemical properties of vardenafil hydrochloride (VAR), its amorphous form and combinations with excipients-hydroxypropyl methylcellulose (HPMC) and β-cyclodextrin (β-CD)-were prepared. The impact of the modification on physicochemical properties was estimated by comparing amorphous mixtures of VAR to their crystalline form. The amorphous form of VAR was obtained as a result of the freeze-drying process. Confirmation of the identity of the amorphous dispersion of VAR was obtained through the use of comprehensive analysis techniques-X-ray powder diffraction (PXRD) and differential scanning calorimetry (DSC), supported by FT-IR (Fourier-transform infrared spectroscopy) coupled with density functional theory (DFT) calculations. The amorphous mixtures of VAR increased its apparent solubility compared to the crystalline form. Moreover, a nearly 1.3-fold increase of amorphous VAR permeability through membranes simulating gastrointestinal epithelium as a consequence of the changes of apparent solubility (P_{app crystalline VAR} = 6.83 × 10^-6 cm/s vs. P_{app amorphous VAR} = 8.75 × 10^-6 cm/s) was observed, especially for its combinations with β-CD in the ratio of 1:5-more than 1.5-fold increase (P_{app amorphous VAR} = 8.75 × 10^-6 cm/s vs. P_{app amorphous VAR:β-CD 1:5} = 13.43 × 10^-6 cm/s). The stability of the amorphous VAR was confirmed for 7 months. The HPMC and β-CD are effective modifiers of its apparent solubility and permeation through membranes simulating gastrointestinal epithelium, suggesting a possibility of a stronger pharmacological effect.

Solubilization and thermodynamic properties of simvastatin in various micellar solutions of different non-ionic surfactants: Computational modeling and solubilization capacity

The aim of this work was to solubilize simvastatin (SIM) using different micellar solutions of various non-ionic surfactants such as Tween-80 (T80), Tween-20 (T20), Myrj-52 (M52), Myrj-59 (M59), Brij-35 (B35) and Brij-58 (B58). The solubility of SIM in water (H2O) and different micellar concentrations of T80, T20, M52, M59, B35 and B58 was determined at temperatures T = 300.2 K to 320.2 K under atmospheric pressure p = 0.1 MPa using saturation shake flask method. The experimental solubility data of SIM was regressed using van't Hoff and Apelblat models. The solubility of SIM (mole fraction) was recorded highest in M59 (1.54 x 10-2) followed by M52 (6.56 x 10-3), B58 (5.52 x 10-3), B35 (3.97 x 10-3), T80 (1.68 x 10-3), T20 (1.16 x 10-3) [the concentration of surfactants was 20 mM in H2O in all cases] and H2O (1.94 x 10-6) at T = 320.2 K. The same results were also recorded at each temperature and each micellar concentration of T80, T20, M52, M59, B35 and B58. "Apparent thermodynamic analysis" showed endothermic and entropy-driven dissolution/solubilization of SIM in H2O and various micellar solutions of T80, T20, M52, M59, B35 and B58.

Insights into co-amorphous systems in therapeutic drug delivery

Co-amorphous (CAM) systems are promising drug-delivery systems in the arena of therapeutic drug delivery, addressing the poor aqueous solubility of drugs by enhancing solubility and thereby improving the oral bioavailability and therapeutic effect of the drug. A CAM system is a single-phase homogeneous blend of two or more low molecular weight molecules that can be drug–drug or drug–co-former, stabilized via intermolecular interactions, adding the benefit of thermodynamic stability. This review covers the fundamentals of CAM systems and recent advances in formulation development. In particular, we strive to address the theoretical, molecular, technical and biopharmaceutical aspects, advantages over polymeric amorphous solid dispersions, mechanisms of stabilization of amorphous forms, insights into unexplored in silico tools in excipient selection and regulatory viewpoints.

Rational Selection of Bio-Enabling Oral Drug Formulations - A PEARRL Commentary

New drug candidates often require bio-enabling formation technologies such as lipid-based formulations, solid dispersions, or nanosized drug formulations. Development of such more sophisticated delivery systems generally requires higher resource investment compared to a conventional oral dosage form, which might slow down clinical development. To achieve the biopharmaceutical objectives while enabling rapid cost effective development, it is imperative to identify a suitable formulation technique for a given drug candidate as early as possible. Hence many companies have developed internal decision trees based mostly on prior organizational experience, though they also contain some arbitrary elements. As part of the EU funded PEARRL project, a number of new decision trees are here proposed that reflect both the current scientific state of the art and a consensus among the industrial project partners. This commentary presents and discusses these, while also going beyond this classical expert approach with a pilot study using emerging machine learning, where the computer suggests formulation strategy based on the physicochemical and biopharmaceutical properties of a molecule. Current limitations are discussed and an outlook is provided for likely future developments in this emerging field of pharmaceutics.

Combining Co-Amorphous-Based Spray Drying with Inert Carriers to Achieve Improved Bioavailability and Excellent Downstream Manufacturability

It is crucial to improve poorly water-soluble orally administered drugs through both preclinical and therapeutic drug discovery. A co-amorphous formulation consisting of two low molecular weight (MW) molecules offers a solubility/dissolubility advantage over its crystalline form by maintaining their amorphous status. Here, we report on a co-amorphous solid dispersion (SD) system that includes inert carriers (lactose monohydrate or microcrystalline cellulose) and co-amorphous sacubitril (SAC)-valsartan (VAL) using the spray drying process. The strong molecular interactions between drugs were the driving force for forming robust co-amorphous SDs. Our system provided the highest solubility with more than ~11.5- and 3.12-times solubility increases when compared with the physical mixtures. Co-amorphous lactose monohydrate (LM) SDs showed better bioavailability of APIs (~356.27.8% and 154.01% for the relative bioavailability of LBQ 657 and valsartan, respectively). Co-amorphous inert carrier SDs possessed an excellent compressibility for the production of a direct compression pharmaceutical product. In conclusion, these brand-new co-amorphous SDs could reduce the number of unit processes to produce a final pharmaceutical product for downstream manufacturability.

Amino acids as stabilizers for spray-dried simvastatin powder for inhalation

BACKGROUND

The use of amino acids as excipients is a promising approach to improve the physical stability and powder dispersibility of spray-dried powders for inhalation.

OBJECTIVES

The aim of this study was to investigate the stabilizing effect of different amino acids on spray-dried amorphous powders for inhalation using simvastatin (SV) as a model compound.

METHODS

Two hydrophobic amino acids (leucine, LEU and tryptophan, TRP), and one hydrophilic amino acid (lysine, LYS) were spray dried from 1% (w/v) solutions with SV at a molar ratio of 1:1 into dry powders for inhalation. Scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were used to characterize the morphology, solid form and potential intermolecular interactions of the spray-dried powders. X-ray photoelectron spectroscopy (XPS) was used to analyse the chemical composition of the surface of the particles. The physical stability of the dry powders was examined upon storage in controlled conditions. A Next generation impactor (NGI) was applied to assess the in vitro aerosol performance of the powders.

RESULTS

XRPD and DSC results confirmed that the spray-dried SV-LEU was composed of crystalline LEU and amorphous SV, the spray-dried SV-LYS was co-amorphous, and the spray-dried SV-TRP was an amorphous system with two phases. XPS analyses revealed that the surface of the spray-dried SV-LEU particles were LEU rich, indicating surface-enrichment of LEU in these particles. In contrast, an almost even distribution of TRP and SV at the surface of spray-dried SV-TRP was observed. FTIR results indicated no intermolecular interaction between SV and the amino acids used in the present study. The three spray-dried samples were physically stable after eight months storage in a desiccator (12% RH, ca. 22 °C). Nevertheless, spray-dried SV-LEU exhibited the best storage stability as compared to the other two spray-dried samples when the samples were stored at 60% RH, 25 °C. Both, the spray-dried SV-LEU and SV-TRP exhibited higher fine particle fractions than the spray-dried SV-LYS.

CONCLUSION

Both the spray-dried SV-LEU and SV-TRP exhibited better aerosol performance and storage stability compared to the spray-dried SV-LYS. Compared to TRP, LEU exhibited better protection of spray-dried amorphous SV from re-crystallization, which could be attributed to the formation of a LEU crystalline shell covering SV upon the spray drying process.

Molecular Dynamics and Physical Stability of Pharmaceutical Co-amorphous Systems: Correlation Between Structural Relaxation Times Measured by Kohlrausch-Williams-Watts With the Width of the Glass Transition Temperature (ΔTg) and the Onset of Crystallization

The study aims to characterize the structural relaxation times of quench-cooled co-amorphous systems using Kohlrausch-Williams-Watts (KWW) and to correlate the relaxation data with the onset of crystallization. Comparison was also made between the relaxation times obtained by KWW and the width of glass transition temperature (ΔT_g) methods (simple and quick). Differential scanning calorimetry, Fourier-transformed infrared spectroscopy, and polarized light microscopy were used to characterize the systems. Results showed that co-amorphous systems yielded a single T_g and ΔC_p, suggesting the binary mixtures exist as a single amorphous phase. A narrow step change at T_g indicates the systems were fragile glasses. In co-amorphous nap-indo and para-indo, experimental T_gs were in good agreement with the predicted T_g. However, the T_g of co-amorphous nap-cim and indo-cim were 20°C higher than the predicted T_g, possibly due to stronger molecular interactions. Structural relaxation times below the experimental T_g were successfully characterized using the KWW and ΔT_g methods. The comparison plot showed that KWW data are directly proportional to the ½ power of ΔT_g data, after adjusting for a small offset. A moderate positive correlation was observed between the onset of crystallization and the KWW data. Structural relaxation times may be useful predictor of physical stability of co-amorphous systems.

Spray-Dried Amorphous Solid Dispersions of Atorvastatin Calcium for Improved Supersaturation and Oral Bioavailability

Over the past few decades, the amorphous solid dispersions (ASDs) technique has emerged as a promising strategy to enhance the in vitro/in vivo characteristic of hydrophobic drugs. The low aqueous solubility and poor bioavailability of atorvastatin calcium (ATO), a lipid-lowering drug, present challenges for effective drug delivery. The objective of this work was to improve the aqueous solubility, in vitro dissolution, and oral absorption of ATO with amorphous solid dispersion technique prepared by spray-drying method. The optimized ternary formulation comprising of ATO; hydroxypropyl methylcellulose (HPMC), as a hydrophilic polymer; and sodium lauryl sulfate (SLS), as a surfactant, at a weight ratio of 1/1/0.1, showed significant improvement in aqueous solubility by ~18-fold compared to that of the free drug, and a cumulative release of 94.09% compared to a release of 59.32% of the free drug. Further, physicochemical studies via scanning electron microscopy, differential scanning calorimetry, and powder X-ray diffraction revealed a change from the crystalline state of the free drug to its amorphous state in the ASD. Pharmacokinetic analysis in rats demonstrated 1.68- and 2.39-fold increments in AUC and Cmax, respectively, in the ASD over the free drug. Altogether, hydrophilic carrier-based ASDs prepared by the spray-drying technique represent a promising strategy to improve the biopharmaceutical performance of poorly soluble drugs.

Agglomerated novel spray-dried lactose-leucine tailored as a carrier to enhance the aerosolization performance of salbutamol sulfate from DPI formulations

Spray-drying allows to modify the physicochemical/mechanical properties of particles along with their morphology. In the present study, _L-leucine with varying concentrations (0.1, 0.5, 1, 5, and 10% w/v) were incorporated into lactose monohydrate solution for spray-drying to enhance the aerosolization performance of dry powder inhalers containing spray-dried lactose-leucine and salbutamol sulfate. The prepared spray-dried lactose-leucine carriers were analyzed using laser diffraction (particle size), differential scanning calorimetry (thermal behavior), scanning electron microscopy (morphology), powder X-ray diffraction (crystallinity), Fourier transform infrared spectroscopy (interaction at molecular level), and in vitro aerosolization performance (deposition). The results showed that the efficacy of salbutamol sulfate’s aerosolization performance was, in part, due to the introduction of _L-leucine in the carrier, prior to being spray-dried, accounting for an increase in the fine particle fraction (FPF) of salbutamol sulfate from spray-dried lactose-leucine (0.5% leucine) in comparison to all other carriers. It was shown that all of the spray-dried carriers were spherical in their morphology with some agglomerates and contained a mixture of amorphous, α-lactose, and β-lactose. It was also interesting to note that spray-dried lactose-leucine particles were agglomerated during the spray-drying process to make coarse particles (volume mean diameter of 79 to 87 μm) suitable as a carrier in DPI formulations.

Dipeptides as co-formers in co-amorphous systems

Drug-amino acid co-amorphous systems have become increasingly well-investigated systems to improve dissolution rate of poorly water-soluble drugs. In this study, dipeptides were investigated as co-formers for co-amorphous systems based on the hypothesis that dipeptides might combine the inherent properties of the two included amino acids. Co-amorphization of the model drug mebendazole was investigated with five dipeptides, tryptophan-phenylalanine, phenylalanine-tryptophan, aspartic acid-tyrosine, histidine-glycine and proline-tryptophan. The dipeptides were chosen to investigate whether the side chains (nonpolar, polar, basic and acidic), and the sequence of amino acids (tryptophan-phenylalanine versus phenylalanine-tryptophan) have an influence on the performance of dipeptides as co-formers. All mebendazole-dipeptide systems became amorphous after ball milling for only 30 min, while this generally was not the case for the single amino acids or physical mixtures of the amino acids forming the dipeptides. Dissolution studies showed that the dissolution rate of mebendazole from most co-amorphous systems was increased significantly compared to crystalline and amorphous mebendazole. However, no clear trend for the drug dissolution enhancement was observed within the different co-amorphous drug-dipeptide systems. The stability study revealed that co-amorphous mebendazole-dipeptide systems showed higher physical stability compared to amorphous mebendazole. In conclusion, dipeptides are shown to be promising co-formers for co-amorphous systems.

Preparation and characterization of multi-component tablets containing co-amorphous salts: Combining multimodal non-linear optical imaging with established analytical methods

Co-amorphous mixtures have rarely been formulated as oral dosage forms, even though they have been shown to stabilize amorphous drugs in the solid state and enhance the dissolution properties of poorly soluble drugs. In the present study we formulated tablets consisting of either spray dried co-amorphous ibuprofen-arginine or indomethacin-arginine, mannitol or xylitol and polyvinylpyrrolidone K30 (PVP). Experimental design was used for the selection of tablet compositions, and the effect of tablet composition on tablet characteristics was modelled. Multimodal non-linear imaging, including coherent anti-Stokes Raman scattering (CARS) and sum frequency/second harmonic generation (SFG/SHG) microscopies, as well as scanning electron microscopy, X-ray diffractometry and Fourier-transform infrared spectroscopy were utilized to characterize the tablets. The tablets possessed sufficient strength, but modelling produced no clear evidence about the compaction characteristics of co-amorphous salts. However, co-amorphous drug-arginine mixtures resulted in enhanced dissolution behaviour, and the PVP in the tableting mixture stabilized the supersaturation. The co-amorphous mixtures were physically stable during compaction, but the excipient selection affected the long term stability of the ibuprofen-arginine mixture. CARS and SFG/SHG proved feasible techniques in imaging the component distribution on the tablet surfaces, but possibly due to the limited imaging area, recrystallization detected with x-ray diffraction was not detected.

Engineering Cocrystals of PoorlyWater-Soluble Drugs to Enhance Dissolution in Aqueous Medium

Biopharmaceutics Classification System (BCS) Class II and IV drugs suffer from poor aqueous solubility and hence low bioavailability. Most of these drugs are hydrophobic and cannot be developed into a pharmaceutical formulation due to their poor aqueous solubility. One of the ways to enhance the aqueous solubility of poorlywater-soluble drugs is to use the principles of crystal engineering to formulate cocrystals of these molecules with water-soluble molecules (which are generally called coformers). Many researchers have shown that the cocrystals significantly enhance the aqueous solubility of poorly water-soluble drugs. In this review, we present a consolidated account of reports available in the literature related to the cocrystallization of poorly water-soluble drugs. The current practice to formulate new drug cocrystals with enhanced solubility involves a lot of empiricism. Therefore, in this work, attempts have been made to understand a general framework involved in successful (and unsuccessful) cocrystallization events which can yield different solid forms such as cocrystals, cocrystal polymorphs, cocrystal hydrates/solvates, salts, coamorphous solids, eutectics and solid solutions. The rationale behind screening suitable coformers for cocrystallization has been explained based on the rules of five i.e., hydrogen bonding, halogen bonding (and in general non-covalent bonding), length of carbon chain, molecular recognition points and coformer aqueous solubility. Different techniques to screen coformers for effective cocrystallization and methods to synthesize cocrystals have been discussed. Recent advances in technologies for continuous and solvent-free production of cocrystals have also been discussed. Furthermore, mechanisms involved in solubilization of these solid forms and the parameters influencing dissolution and stability of specific solid forms have been discussed. Overall, this review provides a consolidated account of the rationale for design of cocrystals, past efforts, recent developments and future perspectives for cocrystallization research which will be extremely useful for researchers working in pharmaceutical formulation development.

The relevance of co-amorphous formulations to develop supersaturated dosage forms: In-vitro, and ex-vivo investigation of Ritonavir-Lopinavir co-amorphous materials

Ritonavir and Lopinavir have previously been demonstrated to decrease the maximum solubility advantage and flux in the presence of each other. The present study investigated the ability of Ritonavir and Lopinavir co-amorphous materials to generate a supersaturated state. Further, it explored the precipitation and flux behavior of co-amorphous materials. The co-amorphous materials of Ritonavir and Lopinavir were prepared by quench cool method and characterized in the solid state using XRPD, DSC, FTIR. The solubility studies were conducted in USP phosphate buffer (pH 6.8) for 12 h. The supersaturation potential and precipitation behavior were studied employing pH shift method. Further, the diffusion behavior was explored in vitro and ex-vivo using a semipermeable membrane and intestinal everted sac method, respectively. The results showed that the co-amorphous materials have the potential to generate a supersaturated state. However, the reduction in the amorphous solubility was observed for both the drug(s) and the degree of reduction was found proportionate with the mole fraction of the compound in the co-amorphous material. Interestingly, the flux of both the drugs from co-amorphous material of 2:1 M ratio (Ritonavir 2: Lopinavir 1) was found exceeding the flux of the individual drugs in the amorphous form. The significant increase in the flux was attributed to the improved drug release properties due to precipitation of drug rich phase of nano/micro dimensions.

Co-Amorphous Solid Dispersions for Solubility and Absorption Improvement of Drugs: Composition, Preparation, Characterization and Formulations for Oral Delivery

The amorphous solid state offers an improved apparent solubility and dissolution rate. However, due to thermodynamic instability and recrystallization tendencies during processing, storage and dissolution, their potential application is limited. For this reason, the production of amorphous drugs with adequate stability remains a major challenge and formulation strategies based on solid molecular dispersions are being exploited. Co-amorphous systems are a new formulation approach where the amorphous drug is stabilized through strong intermolecular interactions by a low molecular co-former. This review covers several topics applicable to co-amorphous drug delivery systems. In particular, it describes recent advances in the co-amorphous composition, preparation and solid-state characterization, as well as improvements of dissolution performance and absorption are detailed. Examples of drug-drug, drug-carboxylic acid and drug-amino acid co-amorphous dispersions interacting via hydrogen bonding, π−π interactions and ionic forces, are presented together with corresponding final dosage forms.

Influence of Solvent Composition on the Performance of Spray-Dried Co-Amorphous Formulations

Ball-milling is usually used to prepare co-amorphous drug–amino acid (AA) mixtures. In this study, co-amorphous drug–AA mixtures were produced using spray-drying, a scalable industrially preferred preparation method. The influence of the solvent type and solvent composition was investigated. Mixtures of indomethacin (IND) and each of the three AAs arginine, histidine, and lysine were ball-milled and spray-dried at a 1:1 molar ratio, respectively. Spray-drying was performed at different solvent ratios in (a) ethanol and water mixtures and (b) acetone and water mixtures. Different ratios of these solvents were chosen to study the effect of solvent mixtures on co-amorphous formulation. Residual crystallinity, thermal properties, salt/partial salt formation, and powder dissolution profiles of the IND–AA mixtures were investigated and compared to pure crystalline and amorphous IND. It was found that using spray-drying as a preparation method, all IND–AA mixtures could be successfully converted into the respective co-amorphous forms, irrespective of the type of solvent used, but depending on the solvent mixture ratios. Both ball-milled and spray-dried co-amorphous samples showed an enhanced dissolution rate and maintained supersaturation compared to the crystalline and amorphous IND itself. The spray-dried samples resulting in co-amorphous samples were stable for at least seven months of storage.

Atorvastatin as a Promising Crystallization Inhibitor of Amorphous Probucol: Dielectric Studies at Ambient and Elevated Pressure

The aim of this article was to check the physical stability of the amorphous form of probucol at both standard storage and manufacturing conditions. Our studies clearly show that disordered form of the examined, cholesterol lowering, agent stored at ambient pressure does not reveal any tendency toward recrystallization. The physical stability of neat probucol stored at ambient pressure has been investigated (i) at room temperature by means of X-ray diffraction technique (XRD) as well as (ii) at T = 333 K by means of broadband dielectric spectroscopy (BDS). Due to the fact that compression is an important stage of drugs manufacturing we additionally performed physical stability tests of amorphous probucol at elevated pressure. The recrystallization tendency of the examined pharmaceutical has been tracked online from the initial and further up to a few hours after compression by means of the high pressure BDS technique. These experiments indicate that even very small pressure applied during the sample compression immediately induce its recrystallization. Since, the sensitivity on pressure eliminates probucol from the group of physically stable amorphous APIs, its stabilization is required. Taking into account that there are many scientific reports describing the positive effect of coadministration of probucol with the drug atorvastatin, we used the latter as probucol's crystallization inhibitor.

Amorphous solid dispersions: Rational selection of a manufacturing process

Amorphous products and particularly amorphous solid dispersions are currently one of the most exciting areas in the pharmaceutical field. This approach presents huge potential and advantageous features concerning the overall improvement of drug bioavailability. Currently, different manufacturing processes are being developed to produce amorphous solid dispersions with suitable robustness and reproducibility, ranging from solvent evaporation to melting processes. In the present paper, laboratorial and industrial scale processes were reviewed, and guidelines for a rationale selection of manufacturing processes were proposed. This would ensure an adequate development (laboratorial scale) and production according to the good manufacturing practices (GMP) (industrial scale) of amorphous solid dispersions, with further implications on the process validations and drug development pipeline.