Itraconazole Nanosuspensions via Dual Centrifugation Media Milling: Impact of Formulation and Process Parameters on Particle Size and Solid-State Conversion as Well as Storage Stability

Comparative analysis of polystyrene versus zirconia beads on breakage kinetics, heat generation, and amorphous formation during wet bead milling

This study determined process conditions under which polystyrene (CPS) and zirconia (YSZ) beads cause similar breakage kinetics and temperature rise during manufacturing of drug nanosuspensions via wet bead milling and explored relative advantages of CPS beads, particularly for stress-sensitive compounds. Besides temperature and particle size measurements, a microhydrodynamic-based kinetic model simulated the conditions for CPS to achieve breakage rates equivalent to those of YSZ. A power law correlation was applied to find conditions conducive to temperature equivalency. The maximum contact pressure and pseudo energy dissipation rate were calculated under these equivalency conditions. When bead loading for CPS was increased to match with YSZ, lower temperature at similar breakage conditions or faster breakage at the same temperature was achieved. Increasing the tip speed did not provide any notable advantages for CPS over YSZ in terms of breakage kinetics or temperature. However, under all conditions investigated, CPS beads exhibited markedly lower maximum contact pressure and pseudo energy dissipation rate, which may correlate with reduced mechanically induced amorphization during milling. A proof-of-concept study demonstrated that a mechanical stress-sensitive drug had lower amorphous generation with CPS compared to YSZ. Therefore, CPS beads are a promising alternative to YSZ beads, especially when used at the highest feasible loading.

Small-scale aqueous suspension preparation using dual centrifugation: the effect of process parameters on the sizes of drug particles

The dual centrifugation approach has in the recent years emerged as a powerful milling tool to prepare pharmaceutical suspensions in submicron range with a fast-milling capacity by milling 40 samples simultaneously in 2 mL vials. While there is some standardized milling conditions described in the literature when preparing aqueous suspensions with dual centrifugation, a more systematic and experimental understanding of the milling process to evaluate the impact of different process variables in the dual centrifuge on the final sizes of the suspended drug particles independent of the drug compound used was desired. Overall, the present study demonstrated the applicability of the dual centrifuge for small-scale screening purposes and showed the impact of process parameters on the physical attributes of prepared suspensions. In the present work, the rate of size reduction on three different model compounds, i.e., cinnarizine, haloperidol, and indomethacin, was found to be mostly influenced by the milling speed, size of milling beads, and the bead loading during milling, whereas the rotor temperature did not affect the particle size profiles when stabilized with polysorbate 20 during milling with dual centrifugation. Smaller particle sizes were in general obtained at the highest milling intensity, i.e., 1500 rpm, smallest bead size, i.e., 0.2 mm, and higher bead loadings (42 %, 56 %, and 83 %). The grinding limit of approximately 0.50 µm, 0.70 µm, and 0.35 µm for cinnarizine, haloperidol, and indomethacin, respectively, was achieved relatively fast, i.e., 30 min of milling at the specified conditions, compared to when suspensions were milled with larger bead sizes (i.e., 1.0 mm), lower milling intensities (e.g., 1000 rpm), and lower bead loadings (e.g., 14 or 28 %). The study further confirmed that a higher milling intensity was necessary during milling of haloperidol suspensions probably due to the compounds predominantly plastic properties. Sizes of indomethacin particles increased with longer milling runs up to 240 min and also higher bead loadings of 56 % and 83 %. These observations were further supported by the color conversion from white to yellow of indomethacin suspensions which indicated generation of small quantities of amorphic material after milling with a high milling intensity. Upscale investigations showed comparable particle size profiles for all three model compounds while milling at 1500 rpm for five minutes.

Machine learning strengthened formulation design of pharmaceutical suspensions

Many different formulation strategies have been investigated to oppose suboptimal treatment of long-term or chronic conditions, one of which are the nano- and microsuspensions prepared as long-acting injectables to prolong the release of an active pharmaceutical compound for a defined period of time by regulating the size of particles by milling. Typically, surfactant and/or polymers are added in the dispersion medium of the suspension during processing for stabilization purposes. However, current formulation investigations with milling are heavily based on prior expertise and trial-and-error approaches. Various interacting parameters such as the milling bead size, stabilizer type and concentration have confounded the investigation of milling process. The present study systematically exploited statistical and machine learning (ML) strategies to understand the relationship between suspension characteristics and formulation parameters under full-factorial milling experiments. Stabilizer concentration was identified as a significant factor (p < 0.001) for median suspension diameter (D50). A formulation stability classification ML model with high prediction accuracy (0.91) and F1-score (0.91) under 10-fold cross-validation was constructed based on 72 formulation datapoints. Model interpretation through Shapley additive explanations (SHAP) revealed the prominent impact of stabilizer concentration and milling bead size on formulation stability. The present work demonstrated the potential to achieve a deeper understanding of the design and optimization of nano- and microsuspensions through explainable ML modelling on formulation screening data.

Preparation, characterization, and ex vivo evaluation of isoxanthohumol nanosuspension

This study assessed the equilibrium solubility, oil-water distribution coefficient, and dissociation constant of Isoxanthohumol (IXN), and formulated IXN nanoparticles (IXN-Nps) using a micro media grinding method. The research characterized the particle size, polydispersity index, zeta potential, morphology, and structure of the nanoparticles, and evaluated the optimal cryoprotectant. Additionally, the study examined the toxicity and in vitro and in vivo release of IXN on HT-29 cells. IXN is classified as a Biopharmaceutical Classification System (BCS) II class drug with weak acidity. The average particle size of IXN-Nps is 249.500 nm, with a polydispersity index (PDI) of 0.149 and a zeta potential of -25.210 mV. The research identified 5 % mannitol as the optimal cryoprotectant. Compared to IXN, the half-maximal inhibitory concentration of IXN-Nps decreased to one-third, demonstrating a significant inhibitory effect on HT-29 colon cancer cells. The in vitro cumulative release rate of IXN-Nps within 24 h was 3.5 times higher than that of the IXN solution. In vivo pharmacokinetic results revealed that the oral bioavailability of IXN-Nps increased significantly by 2.8 times compared to the IXN solution. The correlation coefficient (r = 0.9227) exceeded the critical value for significance at the 0.01 (r = 0.834) level, indicating a strong correlation between in vivo and in vitro results. Consequently, the nanosuspension overcame the low solubility limitation of IXN and proved to be an effective method for enhancing the oral bioavailability of IXN.

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 roller milling - the low energy wet bead media milling - a reproducible and robust milling method for formulation investigation of aqueous suspensions?

Long-acting injectables have shown to offer a prolonged release of a drug compound up to several months, providing the opportunity to increase patient compliance for treatment of long-term and chronic conditions. Different formulation technologies have already been utilized for long-acting injectables, and especially aqueous suspensions with crystalline drug particles in the sub-micron range have sparked an interest for future development of long-acting injectables. Wet bead milling is a common top-down process used to prepare nano- and microsuspensions of crystalline drug particles with the addition of surfactants in the dispersion medium, which are working as stabilizers to prevent agglomeration or crystal growth that ultimately may influence the physical stability of nano- and microsuspensions. To examine the reproducibility of the suspensions manufactured and the behavior of their physical stability, i.e., changes in particle sizes over time, low-energy roller mill was utilized for the manufacturing of nano- and microsuspensions in the present study. Investigated formulation parameters was stabilizer type and concentration and milling parameters varied in bead size and duration of milling. The obtained results demonstrated that the physical stability of suspensions containing the two model compounds, cinnarizine and indomethacin, was highly affected by the constitution of surfactant and processing. Various size classes were obtained and accompanied by high variations between the individual samples that indicated uneven and unpredictable milling by the low-energy roller mill, limiting the possibility to prepare reproducible and physical stable suspensions. Short-term stability studies revealed clear tendencies towards reversed Ostwald ripening of suspensions stabilized with poloxamer 188 that contained cinnarizine as the drug compound, and to a smaller extent suspensions containing indomethacin. Furthermore, X-ray Powder Diffraction confirmed no alteration of the drug compounds crystal structure after roller milling for multiple days.

Wet bead milling by dual centrifugation - An approach to obtain reproducible and differentiable suspensions

Aqueous nano- and microsuspensions containing poorly water-soluble, crystalline drug particles have in the recent years sparked an interest for the preparation of long-acting injectables (LAIs), which increase patient compliance for patients treated for long-term or chronic conditions. Nano- and microsuspensions are often prepared by top-down methods, such as wet bead milling, with the addition of stabilizers in the dispersion media, such as surfactants, which influence the particle sizes and physical stability of the suspension. To improve the efficacy of formulation screening for nano- and microsuspensions, dual centrifugation was utilized in this study whereby 40 samples could be manufactured simultaneously to support the formulation definition. Hence, the type and concentration of stabilizer as well as bead size and milling speed was investigated throughout the presented study, but also the ability of the method to produce consistent data was investigated. The obtained results demonstrated that the particle profile obtained after milling was very consistent from run to run and so was the observed stability data, i.e., running n = 1 experiment per combination could clearly be justified as a predictable approach for the formulation screening. The data also showed that the stabilizer, as well as its concentration highly influenced the physical stability of suspensions containing both the two investigated model compounds, i.e., both cinnarizine and indomethacin, where the biggest increase in particle sizes was observed within the first week. For short-term studies, polysorbate 20 was found to be a suitable stabilizer for suspensions of cinnarizine, whereas sodium dodecyl sulphate was more suitable for indomethacin suspensions immediately after the milling even with 1% (w/v) stabilizer solution, but not sufficient for short-term stability due to an insufficient stabilizer concentration. Smaller particles sizes could be achieved by milling the suspensions with the smallest bead sizes and at the highest speed of 1500 rpm without disrupting the crystal structure of the active pharmaceutical ingredient (API), which was confirmed by X-ray Powder Diffraction.

Preparation of Nanosized Pharmaceutical Formulations by Dual Centrifugation

Dual centrifugation (DC) is an innovative in-vial homogenization and in-vial nanomilling technique that has been in use for the preparation of liposomes for more than one decade. Since then, DC has continuously been developed for preparing various liposomes and other lipid nanoparticles including emulsions and solid lipid nanoparticles (SLNs) as well as polymersomes and nanocrystals. Improvements in equipment technology have been achieved over the past decade, so that DC is now on its way to becoming the quasi-standard for the simple, fast, and aseptic production of lipid nanoparticles and nanocrystals in small and medium batch sizes, including the possibility of simple and fast formulation screening or bedside preparations of therapeutic nanoparticles. More than 68 publications in which DC was used to produce nanoparticles have appeared since then, justifying an initial review of the use of DC for pharmaceutical nanotechnology.

Formulation Strategies of Nanosuspensions for Various Administration Routes

Nanosuspensions (NSs), which are nanosized colloidal particle systems, have recently become one of the most interesting substances in nanopharmaceuticals. NSs have high commercial potential because they provide the enhanced solubility and dissolution of low-water-soluble drugs by means of their small particle sizes and large surface areas. In addition, they can alter the pharmacokinetics of the drug and, thus, improve its efficacy and safety. These advantages can be used to enhance the bioavailability of poorly soluble drugs in oral, dermal, parenteral, pulmonary, ocular, or nasal routes for systemic or local effects. Although NSs often consist mainly of pure drugs in aqueous media, they can also contain stabilizers, organic solvents, surfactants, co-surfactants, cryoprotectants, osmogents, and other components. The selection of stabilizer types, such as surfactants or/and polymers, and their ratio are the most critical factors in NS formulations. NSs can be prepared both with top-down methods (wet milling, dry milling, high-pressure homogenization, and co-grinding) and with bottom-up methods (anti-solvent precipitation, liquid emulsion, and sono-precipitation) by research laboratories and pharmaceutical professionals. Nowadays, techniques combining these two technologies are also frequently encountered. NSs can be presented to patients in liquid dosage forms, or post-production processes (freeze drying, spray drying, or spray freezing) can also be applied to transform the liquid state into the solid state for the preparation of different dosage forms such as powders, pellets, tablets, capsules, films, or gels. Thus, in the development of NS formulations, the components/amounts, preparation methods, process parameters/levels, administration routes, and dosage forms must be defined. Moreover, those factors that are the most effective for the intended use should be determined and optimized. This review discusses the effect of the formulation and process parameters on the properties of NSs and highlights the recent advances, novel strategies, and practical considerations relevant to the application of NSs to various administration routes.

Insight into the mechanism behind oral bioavailability-enhancement by nanosuspensions through combined dissolution/permeation studies

As numerous new drug candidates are poorly water soluble, enabling formulations are needed to increase their bioavailability for oral administration. Nanoparticles are a conceptually simple, yet resource consuming strategy for increasing drug dissolution rate, as predicting in vivo oral absorption using in vitro dissolution remains difficult. The objective of this study was to obtain insight into nanoparticle characteristics and performance utilizing an in vitro combined dissolution/permeation setup. Two examples of poorly soluble drugs were examined (cinnarizine and fenofibrate). Nanosuspensions were produced by top-down wet bead milling using dual asymmetric centrifugation, obtaining particle diameters of approx. 300 nm. DSC and XRPD studies indicated that nanocrystals of both drugs were present with retained crystallinity, however with some disturbances. Equilibrium solubility studies showed no significant increase in drug solubility over the nanoparticles, as compared to the raw APIs. Combined dissolution/permeation experiments revealed significantly increased dissolution rates for both compounds compared to the raw APIs. However, there were substantial differences between the dissolution curves of the nanoparticles as fenofibrate exhibited supersaturation followed by precipitation, whereas cinnarizine did not exhibit any supersaturation, but instead a shift towards faster dissolution rate. Permeation rates were found significantly increased for both nanosuspensions when compared to the raw APIs, indicating a direct implication that formulation strategies are needed, be it stabilization of supersaturation by precipitation inhibition and/or dissolution rate enhancement. This study indicates that in vitro dissolution/permeation studies can be employed to better understand the oral absorption enhancement of nanocrystal formulations.

Tailoring the Lamellarity of Liposomes Prepared by Dual Centrifugation

Dual centrifugation (DC) is a new and versatile technique for the preparation of liposomes by in-vial homogenization of lipid-water mixtures. Size, size distribution, and entrapping efficiencies are strongly dependent on the lipid concentration during DC-homogenization. In this study, we investigated the detailed structure of DC-made liposomes. To do so, an assay to determine the ratio of inner to total membrane surfaces of liposomes (inaccessible surface) was developed based on either time-resolved or steady-state fluorescence spectroscopy. In addition, cryogenic electron microscopy (cryo-EM) was used to confirm the lamellarity results and learn more about liposome morphology. One striking result leads to the possibility of producing a novel type of liposome-small multilamellar vesicles (SMVs) with low PDI, sizes of the order of 100 nm, and almost completely filled with bilayers. A second particularly important finding is that VPGs can be prepared to contain open bilayer structures that will close spontaneously when, after storage, more aqueous phase is added and liposomes are formed. Through this process, a drug can effectively be entrapped immediately before application. In addition, dual centrifugation at lower lipid concentrations is found to produce predominantly unilamellar vesicles.