Preparation and Evaluation of Berberine-Excipient Complexes in Enhancing the Dissolution Rate of Berberine Incorporated into Pellet Formulations.

Berberine is used in the treatment of metabolic syndrome and its low solubility and very poor oral bioavailability of berberine was one of the primary hurdles for its market approval. This study aimed to improve the solubility and bioavailability of berberine by preparing pellet formulations containing drug-excipient complex (obtained by solid dispersion). Berberine-excipient solid dispersion complexes were obtained with different ratios by the solvent evaporation method. The maximum saturation solubility test was performed as a key factor for choosing the optimal complex for the drug-excipient. The properties of these complexes were investigated by FTIR, DSC, XRD and dissolution tests. The obtained pellets were evaluated and compared in terms of pelletization efficiency, particle size, mechanical strength, sphericity and drug release profile in simulated media of gastric and intestine. Solid-state analysis showed complex formation between the drug and excipients used in solid dispersion. The optimal berberine-phospholipid complex showed a 2-fold increase and the optimal berberine-gelucire and berberine-citric acid complexes showed more than a 3-fold increase in the solubility of berberine compared to pure berberine powder. The evaluation of pellets from each of the optimal complexes showed that the rate and amount of drug released from all pellet formulations in the simulated gastric medium were significantly lower than in the intestine medium. The results of this study showed that the use of berberine-citric acid or berberine-gelucire complex could be considered a promising technique to increase the saturation solubility and improve the release characteristics of berberine from the pellet formulation.

Histidine as a versatile excipient in the protein-based biopharmaceutical formulations.

Adequate stabilization is essential for marketed protein-based biopharmaceutical formulations to withstand the various stresses that can be exerted during the pre- and post-manufacturing processes. Therefore, a suitable choice of excipient is a significant step in the manufacturing of such delicate products. Histidine, an essential amino acid, has been extensively used in protein-based biopharmaceutical formulations. The physicochemical properties of histidine are unique among amino acids and could afford multifaceted benefits to protein-based biopharmaceutical formulations. With a pKa of approximately 6.0 at the side chain, histidine has been primarily used as a buffering agent, especially for pH 5.5-6.5. Additionally, histidine exhibited several affirmative properties similar to those of carbohydrates (e.g., sucrose and trehalose) and could therefore be considered to be an alternative approach to established protein-based formulation strategies. The current review describes the general physicochemical properties of histidine, lists all commercial histidine-containing protein-based biopharmaceutical products, and discusses a brief outline of the existing research focused on the versatile applications of histidine, which can act as a buffering agent, stabilizer, cryo-/lyo-protectant, antioxidant, viscosity reducer, and solubilizing agent. The interaction between histidine and proteins in protein-based biopharmaceutical formulations, such as the Donnan effect during diafiltration of monoclonal antibody solutions and the degradation of polysorbates in histidine buffer, has also been discussed. As the first review of histidine in protein biopharmaceuticals, it helps to deepen our understanding of the opportunities and challenges associated with histidine as an excipient for protein-based biopharmaceutical formulations.

System-agnostic prediction of pharmaceutical excipient miscibility via computing-as-a-service and experimental validation.

We applied computing-as-a-service to the unattended system-agnostic miscibility prediction of the pharmaceutical surfactants, Vitamin E TPGS and Tween 80, with Copovidone VA64 polymer at temperature relevant for the pharmaceutical hot melt extrusion process. The computations were performed in lieu of running exhaustive hot melt extrusion experiments to identify surfactant-polymer miscibility limits. The computing scheme involved a massively parallelized architecture for molecular dynamics and free energy perturbation from which binodal, spinodal, and mechanical mixture critical points were detected on molar Gibbs free energy profiles at 180 °C. We established tight agreement between the computed stability (miscibility) limits of 9.0 and 10.0 wt% vs. the experimental 7 and 9 wt% for the Vitamin E TPGS and Tween 80 systems, respectively, and identified different destabilizing mechanisms applicable to each system. This paradigm supports that computational stability prediction may serve as a physically meaningful, resource-efficient, and operationally sensible digital twin to experimental screening tests of pharmaceutical systems. This approach is also relevant to amorphous solid dispersion drug delivery systems, as it can identify critical stability points of active pharmaceutical ingredient/excipient mixtures.

Low-viscosity hydroxypropyl methylcellulose obtained by electron beam irradiation and its performance in spray drying.

Low-viscosity hydroxypropyl methylcellulose (HPMC) was obtained by electron beam irradiation, and its use as an excipient for improving the properties of spray dried pharmaceutical powders was investigated. The minimum molecular weight of HPMC which could maintain the capacity of encapsulation and powder modification was explored. As the irradiation dose was increased from 10 to 200 kGy, the molecular weight and viscosity of HPMC decreased linearly. However, its main structure and degrees of methoxy and hydroxypropyl substitution were not significantly affected. The irradiated HPMC could encapsulate particles during spray drying and, thus, modify powder properties. Furthermore, the water content of spray-dried powders with irradiated HPMC was lower than that with parent HPMC. After the spray-dried powder with irradiated HPMC was prepared into granules, their dissolution rate was also faster. However, in order to achieve high encapsulation, the molecular weight of HPMC should be ensured to be above 7.5 kDa. The designated low-viscosity HPMC obtained by electron beam irradiation is a suitable powder-modification material for use in spray drying, and it shows promise as a superior excipient in medicine, food, paint industries, among others.

Inhalable tobramycin EEG powder formulation for treating Pseudomonas aeruginosa-induced lung infection.

Pulmonary delivery of antibiotics is an effective strategy in treating bacterial lung infection for cystic fibrosis patients, by achieving high local drug concentrations and reducing overall systemic exposure compared to systemic administration. However, the inherent anatomical lung defense mechanisms, formulation characteristics, and drug-device combination determine the treatment efficacy of the aerosol delivery approach. In this study, we prepared a new tobramycin (Tobi) dry powder aerosol using excipient enhanced growth (EEG) technology and evaluated the in vitro and in vivo aerosol performance. We further established a Pseudomonas aeruginosa-induced lung infection rat model using an in-house designed novel liquid aerosolizer device. Notably, novel liquid aerosolizer yields comparable lung infection profiles despite administering 3-times lower P. aeruginosa CFU per rat in comparison to the conventional intratracheal administration. Dry powder insufflator (e.g. Penn-Century DP-4) to administer small powder masses to experimental animals is no longer commercially available. To address this gap, we developed a novel rat air-jet dry powder insufflator (Rat AJ DPI) that can emit 68-70 % of the loaded mass for 2 mg and 5 mg of Tobi-EEG powder formulations, achieving a high rat lung deposition efficiency of 79 % and 86 %, respectively. Rat AJ DPI can achieve homogenous distribution of Tobi EEG powder formulations at both loaded mass (2 mg and 5 mg) over all five lung lobes in rats. We then demonstrated that Tobi EEG formulation delivered by Rat AJ DPI can significantly decrease CFU counts in both trachea and lung lobes at 2 mg (p < 0.05) and 5 mg (p < 0.001) loaded mass compared to the untreated P. aeruginosa-infected group. Tobi EEG powder formulation delivered by the novel Rat AJ DPI showed excellent efficiencies in substantially reducing the P. aeruginosa-induced lung infection in rats.

Sweet corn phytoglycogen dendrimers as a lyoprotectant for dry-state protein storage.

Protein biotherapeutics typically require expensive cold-chain storage to maintain their fold and function. Packaging proteins in the dry state via lyophilization can reduce these cold-chain requirements. However, formulating proteins for lyophilization often requires extensive optimization of excipients that both maintain the protein folded state during freezing and drying (i.e., "cryoprotection" and "lyoprotection"), and form a cake to carry the dehydrated protein. Here we show that sweet corn phytoglycogens, which are glucose dendrimers, can act as both a protein lyoprotectant and a cake-forming agent. Phytoglycogen (PG) dendrimers from 16 different maize sources (PG1-16) were extracted via ethanol precipitation. PG size was generally consistent at ~70-100 nm for all variants, whereas the colloidal stability in water, protein contaminant level, and maximum density of cytocompatibility varied for PG1-16. 10 mg/mL PG1, 2, 9, 13, 15, and 16 maintained the activity of various proteins, including green fluorescent protein, lysozyme, ß-galactosidase, and horseradish peroxidase, over a broad range of concentrations, through multiple rounds of lyophilization. PG13 was identified as the lead excipient candidate as it demonstrated narrow dispersity, colloidal stability in phosphate-buffered saline, low protein contaminants, and cytocompatibility up to 10 mg/mL in NIH3T3 cell cultures. All dry protein-PG13 mixtures had a cake-like appearance and all frozen protein-PG13 mixtures had a Tg' of ~ -26°C. The lyoprotection and cake-forming properties of PG13 were density-dependent, requiring a minimum density of 5 mg/mL for maximum activity. Collectively these data establish PG dendrimers as a new class of excipient to formulate proteins in the dry state.

A drug-excipient interaction impurity of bromhexine hydrochloride injection: Structure and formation mechanism elucidation.

A long-term stability study using high performance liquid chromatography (HPLC) revealed an unidentified impurity in the bromhexine hydrochloride injection, which was employed as a mucolytic agent. Investigations into stress degradation and elemental impurities revealed one of the elemental impurities Fe3+ in this injection as the primary generator of these impurities. This impurity, named N-carboxymethyl bromhexine, was a product formed during drug-excipient interaction between bromhexine and tartaric acid with Fe3+. The structure of the impurity was identified through ultra-high-performance liquid chromatography with diode array detector (UHPLC-DAD), liquid chromatograph mass spectrometer (LC-MS). Further, the formation mechanism of the impurity was discussed. Overall, this study elucidates the cause, origin, and mechanism of an unknown impurity in bromhexine hydrochloride injection, providing a basis for quality control for bromhexine hydrochloride injections and drug products containing both amine and tartaric acid.

Evaluation of starch granules based on hydroxypropylcellulose as a substitute for excipient lactose.

BACKGROUND: The improvement in flowability and adhesion of starch powder (SP) is essential for using starch as an excipient for lactose intolerant patients. In this study, we attempted to evaluate the usefulness of hydroxypropylcellulose with molecular weight 80,000 (HPC-80) in the preparation of the starch granules (SG) as a substitute for excipient lactose. METHODS: Hydroxypropylcellulose with molecular weight 30,000 (HPC-30) and HPC-80 were used as binders to prepare the SG, and defined as HPC-30-SG and HPC-80-SG, respectively. Mean particle size (D50) was measured according to the Method, Optical Microscopy of Particle Size Determination in Japanese Pharmacopoeia, Eighteenth Edition, and storage stability were evaluated by measuring of the physical properties after vortexing the granules for 180 s (physical impact). The product loss rate was calculated from the weight change of the various excipients before and after the one dose packaging (ODP). RESULTS: The D50 of SP (30 µm) was smaller than that of the lactose powder (115 µm). The granulation with 0.75-3% HPC-30 and HPC-80 increased the particle size of SP, and the D50 in 1.5% HPC-30-SG (255 µm) and HPC-80-SG (220 µm) were higher than that of lactose. The excipient was removed from the heat seal of the ODP, and upon visual inspection, a large amount of starchy material was observed to be adhering to the paper in the SP. On the other hand, the low recovery rate in SP was attenuated by the granulation with HPC-30 and HPC-80. In the both HPC-30 and HPC-80, the improvement in recovery rate reached a plateau at 1.5%, and the levels of recovery rate was similar to that of lactose. The recovery rate in the 0.75-3% HPC-30-SG and 0.75% HPC-80-SG were decreased by the physical impact, however, the recovery rate and amount of 1.5% and 3% HPC-80-SG were not affected by the physical impact, and these levels were similar to that of lactose. CONCLUSIONS: The use of HPC-80 as a binder of SG was found to produce a higher quality granule product than conventional HPC-based SG. This finding is useful in streamlining the preparation of starch-based powdered medicine in clinical applications.

Fine excipient materials in carrier-based dry powder inhalation formulations: The interplay of particle size and concentration effects.

The contributions of fine excipient materials to drug dispersibility from carrier-based dry powder inhalation (DPI) formulations are well recognized, although they are not completely understood. To improve the understanding of these contributions, we investigated the influences of the particle size of the fine excipient materials on characteristics of carrier-based DPI formulations. We studied two particle size grades of silica microspheres, with volume median diameters of 3.31 µm and 8.14 µm, as fine excipient materials. Inhalation formulations, each composed of a lactose carrier material, one of the fine excipient materials (2.5% or 15.0% w/w), and a drug (fluticasone propionate) material (1.5% w/w) were prepared. The physical microstructure, the rheological properties, the aerosolization pattern, and the aerodynamic performance of the formulations were studied. At low concentration, the large silica microspheres had a more beneficial influence on the drug dispersibility than the small silica microspheres. At high concentration, only the small silica microspheres had a beneficial influence on the drug dispersibility. The results reveal influences of fine excipient materials on mixing mechanics. At low concentration, the fine particles improved deaggregation and distribution of the drug particles over the surfaces of the carrier particles. The large silica microspheres were associated with a greater mixing energy and a greater improvement in the drug dispersibility than the small silica microspheres. At high concentration, the large silica microspheres kneaded the drug particles onto the surfaces of the carrier particles and thus impaired the drug dispersibility. As a critical attribute of fine excipient materials in carrier-based dry powder inhalation formulations, the particle size demands robust specification setting.

Enhanced Dissolution of Amphotericin B through Development of Amorphous Solid Dispersions Containing Polymer and Surfactants.

Amphotericin B (AmB) is the gold standard for antifungal therapy; however, its poor solubility limits its administration via intravenous infusion. A promising formulation strategy to achieve an oral formulation is the development of amorphous solid dispersions (ASDs) via spray-drying. Inclusion of surfactants into ASDs is a newer concept, yet it offers increased dissolution opportunities when combined with a polymer (HPMCAS 912). We developed both binary ASDs (AmB:HPMCAS 912 or AmB:surfactant) and ternary ASDs (AmB:HPMCAS 912:surfactant) using a variety of surfactants to determine the optimal surfactant carbon chain length and functional group for achieving maximal AmB concentration during in vitro dissolution. The ternary ASDs containing surfactants with a carbon chain length of 14 ± 2 carbons and a sulfate functional group increased the dissolution of AmB by 90-fold compared to crystalline AmB. These same surfactants, when added to a binary ASD, however, were only able to achieve up to a 40-fold increase, alluding to a potential interaction occurring between excipients or excipient and drug. This potential interaction was supported by dynamic light scattering data, in which the ternary formulation produced a single peak at 895.2 dnm. The absence of more than one peak insinuates that all three components are interacting in some way to form a single structure, which may be preventing AmB self-aggregation, thus improving the dissolution concentration of AmB.

Protecting Lyophilized Escherichia coli Adenylate Kinase.

Drying protein-based drugs, usually via lyophilization, can facilitate storage at ambient temperature and improve accessibility but many proteins cannot withstand drying and must be formulated with protective additives called excipients. However, mechanisms of protection are poorly understood, precluding rational formulation design. To better understand dry proteins and their protection, we examine Escherichia coli adenylate kinase (AdK) lyophilized alone and with the additives trehalose, maltose, bovine serum albumin, cytosolic abundant heat soluble protein D, histidine, and arginine. We apply liquid-observed vapor exchange NMR to interrogate the residue-level structure in the presence and absence of additives. We pair these observations with differential scanning calorimetry data of lyophilized samples and AdK activity assays with and without heating. We show that the amino acids do not preserve the native structure as well as sugars or proteins and that after heating the most stable additives protect activity best.

Vaginal drug delivery system: A promising route of drug administration for local and systemic diseases.

Scientists around the globe have done cutting-edge research to facilitate the delivery of poorly absorbed drugs via various routes of administration and different delivery systems. The vaginal route of administration has emerged as a promising mode of drug delivery, attributed to its anatomy and physiology. Novel drug delivery systems overcome the demerits of conventional systems via nanobiotechnology. This review will focus on the disorders associated with women that are currently targeted by vaginal drug delivery systems. In addition, it will provide insights into innovations in drug formulations for the general benefit of women.

Hydrophilic Coating Microstructure Mediates Acute Drug Transfer in Drug-Coated Balloon Therapy.

Drug-coated balloon (DCB) therapy is a promising endovascular treatment for obstructive arterial disease. The goal of DCB therapy is restoration of lumen patency in a stenotic vessel, whereby balloon deployment both mechanically compresses the offending lesion and locally delivers an antiproliferative drug, most commonly paclitaxel (PTX) or derivative compounds, to the arterial wall. Favorable long-term outcomes of DCB therapy thus require predictable and adequate PTX delivery, a process facilitated by coating excipients that promotes rapid drug transfer during the inflation period. While a variety of excipients have been considered in DCB design, there is a lack of understanding about the coating-specific biophysical determinants of essential device function, namely, acute drug transfer. We consider two hydrophilic excipients for PTX delivery, urea (UR) and poly(ethylene glycol) (PEG), and examine how compositional and preparational variables in the balloon surface spray-coating process impact resultant coating microstructure and in turn acute PTX transfer to the arterial wall. Specifically, we use scanning electron image analyses to quantify how coating microstructure is altered by excipient solid content and balloon-to-nozzle spray distance during the coating procedure and correlate obtained microstructural descriptors of coating aggregation to the efficiency of acute PTX transfer in a one-dimensional ex vivo model of DCB deployment. Experimental results suggest that despite the qualitatively different coating surface microstructures and apparent PTX transfer mechanisms exhibited with these excipients, the drug delivery efficiency is generally enhanced by coating aggregation on the balloon surface. We illustrate this microstructure-function relation with a finite element-based computational model of DCB deployment, which along with our experimental findings suggests a general design principle to increase drug delivery efficiency across a broad range of DCB designs.

Investigation on the Combined Effect of Hydroxypropyl Beta-Cyclodextrin (HPßCD) and Polysorbate in Monoclonal Antibody Formulation.

Monoclonal antibodies require careful formulation due to their inherent stability limitations. Polysorbates are commonly used to stabilize mAbs, but they are prone to degradation, which results in unwanted impurities. KLEPTOSE® HPßCD (hydroxypropyl beta-cyclodextrin) has functioned as a stable stabilizer for protein formulations in our previous research. The current study investigates the collaborative impact of combining polysorbates and HPßCD as excipients in protein formulations. The introduction of HPßCD in formulations showed it considerably reduced aggregation in two model proteins, bevacizumab and ipilimumab, following exposure to various stress conditions. The diffusion interaction parameter revealed a reduction in protein-protein interactions by HPßCD. In bevacizumab formulations, the subvisible particle counts per 0.4 mL of samples in commercial formulations vs. formulations containing both HPßCD and polysorbates subjected to distinct stressors were as follows: agitation, 87,308 particles vs. 15,350 particles; light, 25,492 particles vs. 6765 particles; and heat, 1775 particles vs. 460 particles. Isothermal titration calorimetry (ITC) measurement indicated a weak interaction between PS 80 and HPßCD, with a KD value of 74.7 ± 7.5 µM and binding sites of 5 × 10-3. Surface tension measurements illustrated that HPßCD enhanced the surface activity of polysorbates. The study suggests that combining these excipients can improve mAb stability in formulations, offering an alternative for the biopharmaceutical industry.

Pharmaceutical proteins at the interfaces and the role of albumin.

A critical measure of the quality of pharmaceutical proteins is the preservation of native conformations of the active pharmaceutical ingredients. Denaturation of the active proteins in any step before administration into patients could lead to loss of potency and/or aggregation, which is associated with an increased risk of immunogenicity of the products. Interfacial stress enhances protein instability as their adsorption to the air-liquid and liquid-solid interfaces are implicated in the formation of denatured proteins and aggregates. While excipients in protein formulations have been employed to reduce the risk of aggregation, the roles of albumin as a stabilizer have not been reviewed from practical and theoretical standpoints. The amphiphilic nature of albumin makes it accumulate at the interfaces. In this review, we aim to bridge the knowledge gap between interfacial instability and the influence of albumin as a surface-active excipient in the context of reducing the immunogenicity risk of protein formulations.

Exploring paediatric oral suspension development: Challenges, requirements, and formulation advancements.

Oral suspension is the most preferred dosage form for the paediatric population because of the difficulties related to solid medications, such as the swallowing limitations, bitter taste, and poor oral bioavailability, which can cause serious impairment to attain a successful treatment. Given the importance of successful therapies, there is a need for safe and effective commercially-available paediatric oral suspension and their characterization. For the latter, it is important to identify safe excipients and preservatives. The paediatric group is a diverse category which includes infants and teenagers, with major pharmacokinetics and pharmacodynamics differences, mainly because of physiological and behavioral variations. Therefore, finding a single formulation for paediatric population remains a challenge, as well asthe formulation of stable-in-time suspension. In addition, drug's dissolving characteristic and permeation, are the main determinants for oral absorption, which are closely related to drug release kinetics from the pharmaceutical form. In this context, drug release profile is an important and limiting step in oral bioavailability, particularly for BCS class II drugs; thus, it is possible to increase bioavailability and minimize adverse effects by changing the release rate of such drugs. This review covers all the aspects for paediatric oral suspension development, and analyses the considerations for excipients selection as a crucial task for effectively choosing a safe and effective pharmaceutical form and correctly dosing paediatric patients.

A Comprehensive Analysis of Biopharmaceutical Products Listed in the FDA's Purple Book.

Although biopharmaceuticals constitute around 10% of the drug landscape, eight of the ten top-selling products were biopharmaceuticals in 2023. This study did a comprehensive analysis of the FDA's Purple Book database. Firstly, our research uncovered market trends and provided insights into biologics distributions. According to the investigation, although biotechnology has advanced and legislative shifts have made the approval process faster, there are still challenges to overcome, such as molecular instability and formulation design. Moreover, our research comprehensively analyzed biological formulations, pointing out significant strategies regarding administration routes, dosage forms, product packaging, and excipients. In conjunction with biologics, the widespread integration of innovative delivery strategies will be implemented to confront the evolving challenges in healthcare and meet an expanding array of treatment needs.

Utilization and Evaluation of Rice Bran and Rice Bran Wax as a Tablet Lubricant.

The rice bran and rice bran wax of the KJ CMU107 rice strain were investigated as potential tablet lubricants in a directly compressed tablet formulation. Stabilized full-fatted rice bran (sFFRB), stabilized defatted rice bran (sDFRB), and rice bran wax (RBW) extracted and purified from crude rice bran oil (cRBO) were tested. Two commercial lubricants, including magnesium stearate (MGS) and hydrogenated cottonseed oil (HVO), were employed as the standards in the formulated mixtures, which contained spray-dried rice starch (SDRS) as a diluent. The tableting was carried out for each formulation, and the obtained tablets were physically and mechanically evaluated. Among the parameters investigated were the general appearance, ejection force, weight variation, hardness, friability, and disintegration time. The powder flow was also determined for each formulation. The results showed that the tablet ejection forces for all the lubricated formulations (58-259 N) were significantly lower than that of the non-lubricated control formulation (349 N). The use of sFFRB as a lubricant at 0.5-2.0% w/w could lower the ejection force up to 78%, but the hardness reduced so drastically that the formulations failed the friability test due to the chipping of the tablets' edges. Moreover, sDFRB performed significantly better as the use at 0.5-1.0% w/w in the formulation helped to lower the ejection forces by up to 80% while maintaining the changes in the tablet hardness within 10%. RBW functioned effectively as a tablet lubricant at a concentration of 0.5% w/w, yielding tablets with good strength comparable to standard HVO lubricant while helping to reduce the ejection force by 82%. In formulations with good lubrication, i.e., friability < 1%, the powder flow was improved, and the tablet disintegration times were within the same range as the control and HVO formulations. In conclusion, sDFRB displayed a lubricant property at concentrations between 0.5 and 1.0% w/w, with slightly negative effects on the tablet hardness. RBW from KJ CMU107 rice was an effective tablet lubricant at 0.5% w/w, with no effect on tablet hardness. Both materials can be further developed for use as commercial lubricants in direct compression.

Investigation of the Solid-State Interactions in Lyophilized Human G-CSF Using Hydrogen-Deuterium Exchange Mass Spectrometry.

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) previously elucidated the interactions between excipients and proteins for liquid granulocyte colony stimulating factor (G-CSF) formulations, confirming predictions made using computational structure docking. More recently, solid-state HDX mass spectrometry (ssHDX-MS) was developed for proteins in the lyophilized state. Deuterium uptake in ssHDX-MS has been shown for various proteins, including monoclonal antibodies, to be highly correlated with storage stability, as measured by protein aggregation and chemical degradation. As G-CSF is known to lose activity through aggregation upon lyophilization, we applied the ssHDX-MS method with peptide mapping to four different lyophilized formulations of G-CSF to compare the impact of three excipients on local structure and exchange dynamics. HDX at 22 °C was confirmed to correlate well with the monomer content remaining after lyophilization and storage at -20 °C, with sucrose providing the greatest protection, and then phenylalanine, mannitol, and no excipient leading to progressively less protection. Storage at 45 °C led to little difference in final monomer content among the formulations, and so there was no discernible relationship with total deuterium uptake on ssHDX. Incubation at 45 °C may have led to a structural conformation and/or aggregation mechanism no longer probed by HDX at 22 °C. Such a conformational change was observed previously at 37 °C for liquid-formulated G-CSF using NMR. Peptide mapping revealed that tolerance to lyophilization and -20 °C storage was linked to increased stability in the small helix, loop AB, helix C, and loop CD. LC-MS HDX and NMR had previously linked loop AB and loop CD to the formation of a native-like state (N*) prior to aggregation in liquid formulations, suggesting a similar structural basis for G-CSF aggregation in the liquid and solid states.