Process optimization and particle engineering of micronized drug powders via milling

A Systematic Investigation of Process Parameters for Small-Volume Aqueous Suspension Production by the Use of Focused Ultrasonication

Aqueous suspensions containing crystalline drug in the sub-micron range is a favorable platform for long-acting injectables where particle size can be used to obtain a desired plasma-concentration profile. Stabilizers are added to the suspensions and screened extensively to define the optimal formulation composition. In the initial formulation screening the amount of drug compound can be limited, necessitating milling methods for small-volume screening predictable for scale-up. Hence, adaptive focused ultrasound was investigated as a potential milling method for rapid small-volume suspensions by identifying the critical process parameters during preparation. Suspensions containing drug compounds with different mechanical properties and thereby grindability, i.e., cinnarizine, haloperidol, and indomethacin with brittle, elastic, and plastic properties, respectively, were investigated to gain an understanding of the manufacturing with adaptive focused acoustics as well as comparison to already established milling techniques. Using a DoE-design, peak incident power was identified as the most crucial process parameter impacting the milling process for all three compounds. It was possible to decrease the sizes of drug particles to micron range after one minute of focused ultrasound exposure which was superior compared to other milling techniques (e.g., non-focused ultrasound exposure). The addition of milling beads decreased the drug particle sizes even further, thus to a lower degree than other already established milling techniques such as milling by dual centrifugation. This study thereby demonstrated that adaptive focused ultrasonication was a promising method for rapid homogenization and particle size reduction to micron range for different compounds varying in grindability without altering the crystalline structure.

Is Ultrasound as a Milling or Pre-Milling Method to Prepare Aqueous Suspensions an Effective Approach?

High-pressure homogenization is a widely used and acknowledged method to reduce the particle sizes of active pharmaceutical compounds into nanosized range. Thus, the method is associated with limitations, as the compound's initial particle size, since micronized particles are often prerequired to achieve successful size reduction into nanosized range. In this work, the usage of ultrasound as a potential milling or pre-milling technique to decrease particle sizes of different drug compounds varying in deformation properties into micronized range, was investigated.

Emerging Process Modeling Capabilities for Dry Powder Operations for Inhaled Formulations

Dry powder inhaler (DPI) products are commonly formulated as a mixture of micronized drug particles and large carrier particles, with or without additional fine particle excipients, followed by final powder filling into dose containment systems such as capsules, blisters, or reservoirs. DPI product manufacturing consists of a series of unit operations, including particle size reduction, blending, and filling. This review provides an overview of the relevant critical process parameters used for jet milling, high-shear blending, and dosator/drum capsule filling operations across commonly utilized instruments. Further, this review describes the recent achievements regarding the application of empirical and mechanistic models, especially discrete element method (DEM) simulation, in DPI process development. Although to date only limited modeling/simulation work has been accomplished, in the authors' perspective, process design and development are destined to be more modeling/simulation driven with the emphasis on evaluating the impact of material attributes/process parameters on process performance. The advancement of computational power is expected to enable modeling/simulation approaches to tackle more complex problems with better accuracy when dealing with real-world DPI process operations.

Carrier-Free Inhalable Dry Microparticles of Celecoxib: Use of the Electrospraying Technique

Upregulation of cyclooxygenase (COX-2) plays an important role in lung cancer pathogenesis. Celecoxib (CLX), a selective COX-2 inhibitor, may have beneficial effects in COVID-19-induced inflammatory storms. The current study aimed to develop carrier-free inhalable CLX microparticles by electrospraying as a dry powder formulation for inhalation (DPI). CLX microparticles were prepared through an electrospraying method using a suitable solvent mixture at two different drug concentrations. The obtained powders were characterized in terms of their morphology, solid state, dissolution behavior, and aerosolization performance. Electrosprayed particles obtained from the ethanol-acetone solvent mixture with a drug concentration of 3 % w/v exhibited the best in vitro aerosolization properties. The value of the fine particle fraction obtained for the engineered drug particles was 12-fold higher than that of the untreated CLX. When the concentration of CLX was increased, a remarkable reduction in FPF was obtained. The smallest median mass aerodynamic diameter was obtained from the electrosprayed CLX at a 3% concentration (2.82 µm) compared to 5% (3.25 µm) and untreated CLX (4.18 µm). DSC and FTIR experiments showed no change in drug crystallinity or structure of the prepared powders during the electrospraying process. The findings of this study suggest that electrospraying has potential applications in the preparation of DPI formulations.

Development of Low-Cost, Weight-Adjustable Clofazimine Mini-Tablets for Treatment of Tuberculosis in Pediatrics

Clofazimine (CFZ) is an important component of the World Health Organization's (WHO) recommended all-oral drug regimen for treatment of multi-drug resistant tuberculosis (MDR-TB). However, the lack of a dividable oral dosage form has limited the use of the drug in pediatric populations, who may require lowering of the dose to reduce the likelihood of adverse drug events. In this study, pediatric-friendly CFZ mini-tablets were prepared from micronized powder via direct compression. Rapid disintegration and maximized dissolution in GI fluids was achieved using an iterative formulation design process. Pharmacokinetic (PK) parameters of the optimized mini-tablets were obtained in Sprague-Dawley rats and compared against an oral suspension of micronized CFZ particles to examine the effect of processing and formulation on the oral absorption of the drug. Differences in maximum concentration and area under the curve between the two formulations were non-significant at the highest dosing level tested. Variability between rats prevented bioequivalence from being determined according to guidelines outlined by the Food and Drug Administration (FDA). These studies provide an important proof-of-concept for an alternative, low-cost formulation and processing approach for the oral delivery of CFZ in manner that is suitable for children as young as 6 months of age.

Role of dispersion enhancer selection in the development of novel tratinterol hydrochloride dry powder inhalation formulations

Tratinterol hydrochloride (TH) is a new long-acting bronchodilator with strong β₂ adrenoceptor stimulation activity. The aim of this study was to design a new carrier-based dry powder inhalation (DPI) formulation for TH and to investigate the effect of dispersion enhancers on the aerosol performance of TH in vitro. To this end, coarse lactose was used as a carrier. TH was micronized by using a jet mill and blended with the carrier to obtain a reference DPI formulation. Commercial magnesium stearate (MgSt) as received, micronized MgSt (MgSt-M), and fine lactose (FL) were used as the dispersion enhancers and formulated with the micronized TH (TH-M) and the carrier as DPI formulations. The obtained DPI formulations were characterized using dynamic light scattering (DLS), X-ray powder diffraction (XRPD), thermal analysis, powder rheometer, and Raman microscopy. A next generation pharmaceutical impactor (NGI) was used to evaluate the aerodynamic performance of the dry powders. The results showed that TH-M was in an inhalable particle size range, and based on the XRPD and thermal analysis, the solid form of TH-M did not change compared to the starting materials. The NGI results showed that the fine particle fraction (FPF) of TH could be increased with the addition of MgSt and FL as dispersion enhancers in the reference formulation. In addition, the FPF of TH could be increased with a decrease in the particle size of MgSt or an increase in the amount of FL. A combination of MgSt-M and FL could further improve the aerosol performance of TH. Raman spectroscopic imaging confirmed the spatial location of MgSt and TH at the surface of the carrier. This study demonstrates that TH could be formulated into carrier-based dry powder formulation for inhalation using coarse lactose as the carrier. The dual strategy based on using both MgSt and FL as dispersion enhancers improved the aerosol performance of a novel TH dry powder formulation.

Insights into the Impact of Nanostructural Properties on Powder Tribocharging: The Case of Milled Salbutamol Sulfate

The impact of the crystallinity of organic solid materials on their tribocharging propensity is well reported. However, no unequivocal explanation about the potential underlying mechanism(s) could be found so far in the literature. This study reports the effect that different degrees of crystalline disorder has on the tribocharging propensity of a small molecular organic material, salbutamol sulfate (SS). Ball-milling was used to induce structural transformations in the crystalline structure of SS. Particles with different nanostructures were produced and analyzed for their solid-state, particle properties, and tribocharging. It was found that differences in the amorphous content among the processed particles and related moisture levels had an impact on powder tribocharging. A correlation between the latter and the nanostructural properties of the particles was also established. The presence of interfaces between nanodomains of different densities and shorter average lengths within the phases seems to lead to a mitigation of charge. This suggests that undetected, subtle nanostructural differences of materials can affect powder handling and processability by altering their tribocharging. The present findings demonstrate the nanostructural implications of powder triboelectrification, which can help toward the rational design of a wide variety of organic solids.

A critical review on the particle generation and other applications of rapid expansion of supercritical solution

The novel particle generation processes of Active Pharmaceutical Ingredient (API)/drug have been extensively explored in recent decades due to their wide-range applications in the pharmaceutical industry. The Rapid Expansion of Supercritical Solutions (RESS) is one of the promising techniques to obtain the fine particles (micro to nano-size) of APIs with narrow particle size distribution (PSD). In RESS, supercritical carbon dioxide (SC CO₂) and API are used as solvent and solute respectively. In this literature survey, the application of RESS in the formation of fine particles is critically reviewed. Solubility of API in SC CO₂ and supersaturation are the key factors in tuning the particle size. The different approaches to model and predict the solubility of API in SC CO₂ are discussed. Then, the effect of process parameters on mean particle size and the particle size distribution are interpreted in the context of solubility and supersaturation. Furthermore, the less-explored applications of RESS in preparation of solid-lipid nanoparticles, liposome, polymorphic conversion, cocrystallization and inclusion complexation are compared with traditional processes. The solubility enhancement of API in SC CO₂ using co-solvent and its applications in particle generation are explored in published literature. The development and modifications in the conventional RESS process to overcome the limitations of RESS are presented. Finally, the perspective on RESS with special attention to its commercial operation is highlighted.

Role of surface molecular environment and amorphous content in moisture sorption behavior of milled Terbutaline Sulphate

Milling may cause undesired changes in crystal topology, due to exposure of new facets, their corresponding functional groups and surface amorphization. This study investigated effect of milling induced surface amorphous content and chemical environment on moisture sorption behavior of a model hydrophilic drug, Terbutaline Sulphate (TBS). A Dynamic Vapor Sorption (DVS) based analytical method was developed to detect amorphous content, with LOD and LOQ of 0.41% and 1.24%w/w, respectively. The calibration curve gave a linear regression of 0.999 in a concentration range of 0-16.36%w/w amorphous content plotted against surface area normalized % weight change, due to moisture sorption. TBS was milled using air jet mill at 8 Bars for 3 cycles (D₉₀- 3.46µm) and analyzed using the validated DVS method prior to and post conditioning. The moisture sorption was higher in case of milled unconditioned TBS. Molecular Dynamics Simulation (MDS) was performed to identify the cause for increased moisture sorption due to altered surface environment or amorphous content. The results implied that the new planes and functional groups exposed on milling had negligible contribution to moisture sorption and the higher moisture sorption in milled unconditioned TBS was due to surface amorphization. Conditioning under elevated humidity recrystallized the milling-induced surface amorphous content and led to decreased moisture sorption in milled conditioned TBS.

Solid-State Reactivity of Mechano-Activated Simvastatin: Atypical Relation to Powder Crystallinity

The present study investigated the impact of solid-state disorders generated during milling on the chemical reactivity of simvastatin. An amorphous and a partially crystalline simvastatin powders were generated via cryomilling simvastatin crystals for either 90 or 10 min, respectively. The thoroughly characterized milled powders were stored at 40°C/75% RH, in open and closed containers. The effect of milling and storage conditions on physical stability was investigated using simultaneous small and wide-angle X-ray scattering and differential scanning calorimetry. The chemical degradation was evaluated using liquid chromatography-mass spectrometry. Compared with the fully amorphous state, the partially crystalline simvastatin crystallized to a lower extent in the expense of higher chemical degradation on open storage. The closely stored samples degraded to a lower extent and crystallized to a higher extent than the openly stored ones. However, the trends of the total crystallinity and degradation between amorphous and partially crystalline powders were similar. Small-angle X-ray scattering revealed that the partially crystalline simvastatin comprised a higher extent of nanoscale density heterogeneity than the fully amorphous powder. The overall results pointed toward the role of the remaining amorphous content and the nanoscale and mesoscale density heterogeneity on the chemical reactivity in the disordered simvastatin.

Changes in the Solid State of Nicergoline, a Poorly Soluble Drug, Under Different Grinding and Environmental Conditions: Effect on Polymorphism and Dissolution

Nicergoline native crystals (Form I) were subjected to different grinding methods for 15, 30, 45, and 60 min: Method A, grinding at 20°C under air atmosphere; Method B, grinding in presence of liquid nitrogen under air atmosphere; Method C, grinding at 20°C under nitrogen atmosphere; and Method D, grinding in presence of liquid nitrogen under nitrogen atmosphere. Scanning electron microscopy, differential scanning calorimetry, X-ray powder diffractometry, thermogravimetry, and infrared spectroscopy were used to follow changes in the particle size and in crystalline structures. Batches from Methods A and C underwent partial amorphization immediately after grinding; Form II was obtained by heating these partially amorphous forms or after spontaneous crystallization after 1 and 5 months storage. Method B promoted the hydration of nicergoline to a monohydrate form. Batch D was stable under grinding and neither amorphization nor hydration were observed. The best intrinsic dissolution rate was that of metastable Form II, followed by Form I, while the worst was that of the Method B monohydrate form. The slowest particle dissolution was observed for hydrated particles, because of the lowest IDR, while the most rapid was exhibited by batch D, because of the very small particle size.