Hierarchical Particle Approach for Co-Precipitated Amorphous Solid Dispersions for Use in Preclinical In Vivo Studies.

Amorphous solid dispersions (ASD) have become a well-established strategy to improve exposure for compounds with insufficient aqueous solubility. Of methods to generate ASDs, spray drying is a leading route due to its relative simplicity, availability of equipment, and commercial scale capacity. However, the broader industry adoption of spray drying has revealed potential limitations, including the inability to process compounds with low solubility in volatile solvents, inconsistent molecular uniformity of spray dried amorphous dispersions, variable physical properties across batches and scales, and challenges containing potent compounds. In contrast, generating ASDs via co-precipitation to yield co-precipitated amorphous dispersions (cPAD) offers solutions to many of those challenges and has been shown to achieve ASDs comparable to those manufactured via spray drying. This manuscript applies co-precipitation for early safety studies, developing a streamlined process to achieve material suitable for dosing as a suspension in conventional toxicity studies. Development targets involved achieving a rapid, safely contained process for generating ASDs with high recovery yields. Furthermore, a hierarchical particle approach was used to generate composite particles where the cPAD material is incorporated in a matrix of water-soluble excipients to allow for rapid re-dispersibility in the safety study vehicle to achieve a uniform suspension for consistent dosing. Adopting such an approach yielded a co-precipitated amorphous dispersion with comparable stability, thermal properties, and in vivo pharmacokinetics to spray dried amorphous materials of the same composition.

Probing Microenvironmental Acidity in Lyophilized Protein and Vaccine Formulations Using Solid-state NMR Spectroscopy.

Biophysical and biochemical instability of therapeutic proteins in the solution state may necessitate the development of products in the solid form, due to their enhanced stability. Lyophilization is a widely used method to ensure dry state stabilization of biological products. A commonly encountered issue is the pH shifts that can occur due to undesired crystallization of a buffer component, resulting in loss of protein activities. However, it is technically challenging to noninvasively investigate the physicochemical environment in the lyophile matrix. In this work, we demonstrate an approach based on solid-state NMR to investigate the microenvironmental acidity in lyophilized protein formulations, using histidine, a commonly used buffer agent, as a molecular probe. The solid-state acidity in the lyophilized matrix can be assessed by monitoring the chemical shift changes of histidine. The protonation and tautomeric states of histidine lyophilized at a range of pH values from 4.5 to 11.0 were identified from full 13C and 15N resonance assignments in one-dimensional and two-dimensional NMR experiments. The results demonstrated a pH-dependence of histidine chemical shift in the amorphous state. Moreover, we successfully applied this protocol to investigate the microenvironmental pH in lyophilized formulations of the HPV vaccine and lactate dehydrogenase protein.

Modulation of Microenvironmental Acidity: A Strategy to Mitigate Salt Disproportionation in Drug Product Environment.

Disproportionation of pioglitazone hydrochloride (PioHCl), leading to the free base formation, was observed in tablet formulations containing basic excipients such as magnesium stearate (Koranne et al, Mol. Pharmaceutics, 2017, 14, 1133-1144). The nature and concentration of excipients, by modulating the microenvironmental acidity (measured as pHeq), governed the disproportionation reaction. In the current work, we hypothesized that the addition of an organic acid, by lowering the pHeq, can stabilize PioHCl. Powder blends containing PioHCl, magnesium stearate and each oxalic, maleic, tartaric, fumaric, and glutaric acid were stored at 40 °C/75% RH for 15 days. The concentration of crystalline free base, a product of the disproportionation reaction, was quantified using synchrotron radiation. The pHeq of the powder blends was measured via ionization of probe molecules deposited on the surface. In general, the stronger the acid, the lower the pHeq of the formulation blend and more effective it was in stabilizing PioHCl and preventing disproportionation. Thus, controlling the microenvironmental acidity in a rational and systematic way provided an avenue to mitigate excipient-induced salt disproportionation. Even when the lattice of PioHCl was activated by milling, it remained stable in the presence of acid. The amount of water sorbed during tablet storage provided an indirect measure of the disproportionation.

Challenges in Transitioning Cocrystals from Bench to Bedside: Dissociation in Prototype Drug Product Environment.

Tablets containing a theophylline-glutaric acid (TG) cocrystal dissociated rapidly forming crystalline theophylline (20-30%), following storage at 40 °C/75% RH for 2 weeks. Control tablets of TG cocrystal containing no excipients were stable under the same conditions. The dissociation reaction was water-mediated, and the theophylline concentration (the dissociation product), monitored by synchrotron X-ray diffractometry, was strongly influenced by the formulation composition. Investigation of the binary compacts of the TG cocrystal with each excipient revealed the influence of excipient properties (hydrophilicity, ionizability) on cocrystal stability, providing mechanistic insights into a dissociation reaction. Ionizable excipients with a strong tendency to sorb water, for example, sodium starch glycolate and croscarmellose sodium, caused pronounced dissociation. Microcrystalline cellulose (MCC), while a neutral but hydrophilic excipient, also enabled solution-mediated cocrystal dissociation in intact tablets. Magnesium stearate, an ionizable but hydrophobic excipient, interacted with the cocrystal to form a hygroscopic product. The interaction is believed to be initiated in the disordered cocrystal-excipient particle interface. In contrast, the cocrystal was stable in the presence of lactose, a neutral excipient with no tendency to sorb water. The risk of unintended cocrystal dissociation can be mitigated by avoiding contact with water both during processing and storage.

Effect of Formulation and Process Parameters on the Disproportionation of Indomethacin Sodium in Buffered Lyophilized Formulations.

PURPOSE: (i) To investigate buffer salt crystallization and the consequent pH shifts during the freezing stage of the lyophilization of indomethacin sodium (IMCNa) in aqueous sodium phosphate buffer. (ii) To determine the effect of pH shift on the disproportionation of IMCNa in lyophilized formulations. METHODS: Prelyophilization solutions containing IMCNa in sodium phosphate buffer, at initial buffer concentrations ranging from 10 to 100 mM (pH 7.0), and at IMCNa concentrations of 5, 10 & 15 mg/ml, were investigated. Their phase behavior during cooling was monitored by low temperature X- ray diffractometry (XRD), differential scanning calorimetry (DSC) and pH measurements. The final lyophiles were characterized by infrared spectroscopy (IR) and XRD. RESULTS: Upon cooling to -25°C, pronounced pH shifts were observed only in IMCNa buffered solutions containing high initial buffer concentration (100 mM), due to crystallization of Na2HPO4. 12H2O. In the final lyophiles, disproportionation of IMCNa to the free acid (IMC) was observed in systems with buffer concentrations ≥50 mM, but not low buffer concentration (10 mM). At intermediate buffer concentrations (35 & 20 mM) the disproportionation depended on IMCNa concentration. The initial concentrations of both buffer and IMCNa influenced the buffer crystallization. CONCLUSIONS: During freeze drying, selective crystallization of a buffer component and the consequent pH shift can cause disproportionation of IMCNa. This can prolong the reconstitution time or retain particles of the poorly soluble free acid in the reconstituted solution.

Investigation of Spatial Heterogeneity of Salt Disproportionation in Tablets by Synchrotron X-ray Diffractometry.

Tablets which were binary mixtures of pioglitazone hydrochloride (PioHCl) with magnesium stearate (MgSt), croscarmellose sodium (CCS), microcrystalline cellulose, or lactose monohydrate were prepared. Two sets of experiments, using intact tablets, were performed. (i) Tablets containing PioHCl (90% w/w) and MgSt were exposed to 25 or 40 °C and 75% RH in a custom-built temperature/humidity chamber. In situ spatiotemporal mapping of disproportionation was performed by transmission-mode synchrotron X-ray diffractometry (SXRD; Argonne National Laboratories). Tablets were scanned in radial direction starting from the top edge of the tablet and moving, in increments of 300 µm, toward the center. There was evidence of disproportionation after 10 min (at 40 °C). The reaction was initiated on the tablet surface and progressed toward the core. (ii) SXRD of tablets stored for a longer time (up to 15 days) enabled the simultaneous quantification of the reactants and products of disproportionation and provided insight into the reaction progression. The influence of sorbed water and microenvironmental acidity on the disproportionation reaction was investigated. The most pronounced reaction was observed in the presence of MgSt followed by CCS. The transformation was solution-mediated, and the spatial heterogeneity in disproportionation could be explained by the migration of sorbed water. There was a good correlation between microenvironmental acidity (pHeq) and extent of PioHCl disproportionation.