Effect of Structurally Related Compounds on Desupersaturation Kinetics of Indomethacin.

PURPOSE: The pharmaceutical literature contains examples wherein desupersaturation from high concentrations does not proceed to equilibrium concentration of the thermodynamically most stable form but remains above equilibrium. The purpose of the current research was to investigate the effect of structurally related compounds on desupersaturation kinetics as a possible explanation for a higher than equilibrium solubility after crystal growth of γ-indomethacin (γ-IMC). METHODS: Three structurally related compounds (SRC) - cis-sulindac (c-SUL), trans-sulindac (t-SUL) and indomethacin-related compound-A (IMC-A) -were investigated. Desupersaturation kinetics to the most stable γ-IMC, in the presence of c-SUL, t-SUL or IMC-A, was measured at pH 2.0. RESULTS: The SRCs c-SUL and t-SUL were effective crystallization inhibitors of IMC, while IMC-A was not a potent crystallization inhibitor of IMC. Among the sulindac isomers, t-SUL was a stronger crystallization inhibitor. The apparent solubility of γ-IMC crystals grown from supersaturated solutions in the presence of SRCs matched the equilibrium solubility of γ-IMC. During crystallization of IMC in the presence of IMC-A, the concentration of IMC-A declined initially but rebounded as supersaturation and crystallization rate of IMC declined, suggesting that IMC-A itself became incorporated in the IMC crystal lattice at higher degrees of IMC supersaturation. CONCLUSIONS: The results suggest that high apparent solubility after crystallization of IMC reported by several authors is not related to the presence of IMC-A impurity. The greater IMC crystal growth rate inhibition by t-SUL than by c-SUL was consistent with the proposed orientation of SUL molecules adsorbed on the IMC crystal, providing a mechanistic understanding of the inhibition.

Graphene Oxide-Functionalized Thread-Based Electrofluidic Approach for DNA Hybridization.

A novel, low-cost, and disposable thread-based electrofluidic analytical method employing isotachophoresis (ITP) was developed for demonstrating surface DNA hybridization. This approach was based on graphene oxide (GO) surface-functionalized zones on nylon threads as a binding platform to trap a fluorescently labeled isotachophoretically focused single-stranded DNA (ssDNA) band, resulting in quenching of the fluorescence, which signaled quantitative trapping. In the event of an isotachophoretically focused complementary DNA (cDNA) band passing over the GO-trapped ssDNA zone, surface hybridization of the ssDNA and cDNA to form double-stranded DNA (dsDNA) band occurred, which is released from the GO-coated zones, resulting in restoration of the fluorescent signal as it exits the GO band and migrates further along the thread. This controllable process demonstrates the potential of the GO-functionalized thread-based microfluidic analytical approach for DNA hybridization and its visualization, which could be adapted into point-of-care (POC) diagnostic devices for real-world applications.

A thread-based electrofluidic platform for direct transfer, separation, and pre-concentration of materials from sample swabs.

A new method and platform has been developed for direct transfer, electrophoretic separation, and pre-concentration of swabbed samples using the principles of thread-based electrofluidics. A direct electrokinetic injection has been observed for a variety of analytes ranging from small molecules to proteins. The effect of physicochemical interactions of the analyte with the swab and the thread on the transfer efficiency has been studied by exploring different swab and thread combinations. For fluorescein, using a polyurethane swab, 98% and 94% transfer efficiencies were observed on mercerised cotton and nylon thread, while only 80% transfer efficiency was observed on polyester thread, respectively. A 97% transfer of fluorescein was observed on the nylon thread when a flocked nylon swab was used, while only 47% transfer was observed when a cotton swab was used. A successful transfer has been observed for both liquid and dry samples from either pre-wetted or dry swabs in both the presence and absence of any surrounding electrolytes. The platform has been further adapted for multiplexed analysis, where a sample from a single swab was transferred onto two parallel thread systems with ca. 50% distribution between them. The method has been validated for transfer, separation, and pre-concentration of DNA from blood. It has also been successfully used to directly analyse dried blood samples using a commercial sampling device, Neoteryx Mitra.

A Software Tool for Lyophilization Primary Drying Process Development and Scale-up Including Process Heterogeneity, I: Laboratory-Scale Model Testing.

Freeze-drying is a deceptively complex operation requiring sophisticated design of a robust and efficient process that includes understanding and planning for heterogeneity across the batch and shifts in parameters due to vial or lyophilizer changes. A software tool has been designed to assist in process development and scale-up based on a model that includes consideration of the process heterogeneity. Two drug formulations were used to test the ability of the new tool to develop a freeze-drying cycle and correctly predict product temperatures and drying times. Model inputs were determined experimentally, and the primary drying heterogeneous freeze-drying model was used to design drying cycles that provided data to verify the accuracy of model-predicted product temperature and primary drying time. When model inputs were accurate, model-predicted primary drying times were within 0.1 to 15.9% of experimentally measured values, and product temperature accuracy was between 0.2 and 1.2°C for three vial locations, center, inner edge, and outer edge. However, for some drying cycles, differences in vial heat transfer coefficients due to changes in shelf and product temperature as well as altered product resistance due to product temperature-dependent microcollapse increased inaccuracy (up to 28.6% difference in primary drying time and 5.1°C difference in product temperature). This highlights the need for careful determination of experimental conditions used to calculate model inputs. In future efforts, full characterization of location- and shelf temperature-dependentKv as well as location- and product temperature-dependentRp will enhance the accuracy of the predictions by the model within the user-friendly software.

Mechanisms for the Slowing of Desupersaturation of a Weak Acid at Elevated pH.

Supersaturating drug delivery systems are used to achieve higher oral bioavailability for poorly soluble drugs. However, supersaturated solutions often decline to lower concentrations by precipitation and crystallization. The purpose of the current research is to provide a mechanistic understanding of drug crystallization as a function of pH, using indomethacin (IMC, pKa 4.18) as a model compound. Desupersaturation kinetics to the γ-form of IMC was measured at pH 2.0, 3.0, 4.0, and 4.5 from an initial degree of supersaturation of 2.5-6. At equivalent levels of supersaturation, crystal growth rates decreased with an increase in solution pH. Two mechanisms for this phenomenon, reactive diffusion (resulting in a higher surface pH as compared to bulk pH) and inhibition of crystallization by structurally similar ionized IMC at higher pH, were explored. Non-steady-state models for reactive diffusion showed that the surface pH was only 0.01 units above that of the bulk solution pH. Mass transport models for reactive diffusion during crystallization could not explain the decrease in desupersaturation kinetics at higher pH. However, zeta potentials as high as -70 mV suggested that IMC- is adsorbed on the surface of the particles. A mathematical model for inhibition of crystal growth by IMC- accounted for the pH effect suggesting that ionized IMC acts as an effective crystallization inhibitor of IMC.

Formulation design for inkjet-based 3D printed tablets.

The drug loading efficiency was evaluated using a binder-jet 3D printing process by incorporating an active pharmaceutical ingredient (API) in ink, and quantifying the printability property of ink solutions. A dimensionless parameter Ohnesorge was calculated to understand the printability property of the ink solutions. A pre-formulation study was also carried out for the raw materials and printed tablets using thermal analysis and compendial tests. The compendial characterization of the printed tablets was evaluated with respect to weight variation, hardness, disintegration, and size; Amitriptyline Hydrochloride was considered as the model API in this study. Four concentrations of the API ink solutions (5, 10, 20, 40 mg/mL) were used to print four printed tablet batches using the same tablet design file. The excipient mixture used in the study was kept the same and consists of Lactose monohydrate, Polyvinyl pyrrolidone K30, and Di-Calcium phosphate Anhydrate. The minimum drug loading achieved was 30 µg with a minimal variation (RSD) of <0.26%. The distribution of the API on the tablet surface and throughout the printed tablets were observed using SEM-EDS. In contrast, the micro-CT images of the printed tablets indicated the porous surface structure of the tablets. The immediate release properties of the printed tablets were determined using a dissolution study in a modified USP apparatus II.

Nuances in the Calculation of Amorphous Solubility Enhancement Ratio.

The theoretical amorphous solubility enhancement ratio (Rs) can be calculated based on the free energy difference between amorphous and crystalline forms (ΔGx→a), using several experimentally determined input parameters. This work compares the various approaches for the calculation of Rs and explores the nuances associated with its calculation. The uncertainty of Rs values owing to experimental conditions (differential scanning calorimetry heating rates) used to measure the input parameters was determined for 3 drugs (indomethacin, itraconazole, and spironolactone). The calculated value of Rs was most influenced by the measurement of heat of fusion. The range in values of Rs using the various equations in the literature was within the calculated uncertainty of the theoretical Rs value. Still, all equations appear to overpredict the experimental value of Rs, sometimes by more than a factor of 5, when an experimental value is attainable. Methods for the calculation of ΔGx→a for molecules undergoing additional phase transitions (other than glass transition and melting) were developed, employing itraconazole as a model drug. In addition, the influences of enthalpy relaxation and entropy of mixing for racemic compounds on Rs were also considered. These additional corrections improved agreement between theoretical and experimental Rs.

Stability of an Alcohol-free, Dye-free Hydrocortisone (2 mg/mL) Compounded Oral Suspension.

The stability of hydrocortisone in a commercially available dye-free oral vehicle was monitored to establish a beyond-use date for hydrocortisone oral suspension 2 mg/mL. Hydrocortisone oral suspension (2 mg/mL) was prepared from 10-mg tablets in a dye-free oral vehicle (Oral Mix, Medisca) and stored at 4°C and 25°C for 90 days in amber, plastic prescription bottles and oral syringes. The suspendability and dose repeatability of the oral suspension were evaluated. The solubility of hydrocortisone in the dye-free vehicle was determined. Over 90 days, pH and concentration of hydrocortisone in the oral suspension were measured. The stability-indicating nature of a high-pressure liquid chromatographic assay was evaluated in detail. The solubility of hydrocortisone in the dye-free vehicle was 230 mcg/mL at 25°C. This means that about 90% of the drug remains in the solid state where it is less susceptible to degradation. The preparation suspended well to support dose repeatability. The chromatographic assay resolved hydrocortisone from cortisone, excipients in the vehicle, and all degradation products. The assay passed United States Pharmacopeia system suitability tests. Hydrocortisone oral suspension (2 mg/mL) compounded using a dye-free, alcohol-free oral vehicle, Oral Mix, was stable in amber plastic bottles and syringes stored at 4°C and 25°C for 90 days within a 95% confidence interval.

Comparative Assessment of Miniaturized Screening Approaches for Selection of Polymers for Amorphous Drug Stabilization.

The present work highlights the use of miniaturized approaches to screen and prioritize development of solid dispersions that provide stabilization of the amorphous drug against crystallization and enhanced dissolution over the crystalline form. The approaches evaluated include solvent casting and solvent displacement-based techniques. Four compounds were evaluated with both these screening approaches. A dual-pH dilution method using fasted state simulated gastric fluid and fasted state simulated intestinal fluid as media was used to evaluate solubility enhancement ratio in each well of the screen. The concentration at 15 mins after dilution with fasted state simulated intestinal fluid and super-saturation ratio at the end of the dissolution study is used as 2 descriptors of solubility enhancement. The empirical screening approaches were supplemented with theoretical calculations of solubility enhancement to gauge the best-performing amorphous solid dispersion (ASD). Physical stability of the amorphous systems was also evaluated, where applicable. Lead ASD compositions from the screens were scaled up to verify the predictions. To our knowledge, this is the first report where the 2 most common screening approaches for the development of ASDs are compared head to head. These approaches are rapid, material sparing, and can be adapted to accommodate screening of multiple variables such as polymer type, drug load, and ternary systems simultaneously. The strengths, limitations, and most suitable applications for each of the 2 methods are also discussed.

Oral Ingestion and Intraventricular Injection of Curcumin Attenuates the Effort-Related Effects of the VMAT-2 Inhibitor Tetrabenazine: Implications for Motivational Symptoms of Depression.

Effort-related choice tasks are used for studying depressive motivational symptoms such as anergia/fatigue. These studies investigated the ability of the dietary supplement curcumin to reverse the low-effort bias induced by the monoamine storage blocker tetrabenazine. Tetrabenazine shifted effort-related choice in rats, decreasing high-effort lever pressing but increasing chow intake. The effects of tetrabenazine were reversed by oral ingestion of curcumin (80.0-160.0 mg/kg) and infusions of curcumin into the cerebral ventricles (2.0-8.0 µg). Curcumin attenuates the effort-related effects of tetrabenazine in this model via actions on the brain, suggesting that curcumin may be useful for treating human motivational symptoms.