An Enthalpy-Balance Model for Timewise Evolution of Temperature during Wet Stirred Media Milling of Drug Suspensions.

PURPOSE: Nanosuspensions have been used for enhancing the bioavailability of poorly soluble drugs. This study explores the temperature evolution during their preparation in a wet stirred media mill using a coupled experimental-enthalpy balance approach. METHODS: Milling was performed at three levels of stirrer speed, bead loading, and bead sizes. Temperatures were recorded over time, then simulated using an enthalpy balance model by fitting the fraction of power converted to heat ξ. Moreover, initial and final power, ξ, and temperature profiles at 5 different test runs were predicted by power-law (PL) and machine learning (ML) approaches. RESULTS: Heat generation was higher at the higher stirrer speed and bead loading/size, which was explained by the higher power consumption. Despite its simplicity with a single fitting parameter ξ, the enthalpy balance model fitted the temperature evolution well with root mean squared error (RMSE) of 0.40-2.34°C. PL and ML approaches provided decent predictions of the temperature profiles in the test runs, with RMSE of 0.93-4.17 and 1.00-2.17°C, respectively. CONCLUSIONS: We established the impact of milling parameters on heat generation-power and demonstrated the simulation-prediction capability of an enthalpy balance model when coupled to the PL-ML approaches.

Use of Bead Mixtures as a Novel Process Optimization Approach to Nanomilling of Drug Suspensions.

PURPOSE: We aimed to evaluate the feasibility of cross-linked polystyrene (CPS)-yttrium-stabilized zirconia (YSZ) bead mixtures as a novel optimization approach for fast, effective production of drug nanosuspensions during wet stirred media milling (WSMM). METHODS: Aqueous suspensions of 10% fenofibrate (FNB, drug), 7.5% HPC-L, and 0.05% SDS were wet-milled at 3000-4000 rpm and 35%-50% volumetric loading of CPS:YSZ bead mixtures (CPS:YSZ 0:1-1:0 v:v). Laser diffraction, SEM, viscometry, DSC, and XRPD were used for characterization. An nth-order model described the breakage kinetics, while a microhydrodynamic model allowed us to gain insights into the impact of bead materials. RESULTS: CPS beads achieved the lowest specific power consumption, whereas YSZ beads led to the fastest breakage. Breakage followed second-order kinetics. Optimum conditions were identified as 3000 rpm and 50% loading of 0.5:0.5 v/v CPS:YSZ mixture from energy-cycle time-heat dissipation perspectives. The microhydrodynamic model suggests that YSZ beads experienced more energetic/forceful collisions with smaller contact area as compared with CPS beads owing to the higher density-elastic modulus of the former. CONCLUSIONS: We demonstrated the feasibility of CPS-YSZ bead mixtures and rationalized its optimal use in WSMM through their modulation of breakage kinetics, energy utilization, and heat dissipation.

Preparation and characterization of fast dissolving pullulan films containing BCS class II drug nanoparticles for bioavailability enhancement.

The aim of this study is to assess pullulan as a novel steric stabilizer during the wet-stirred media milling (WSMM) of griseofulvin, a model poorly water-soluble drug, and as a film-former in the preparation of strip films via casting-drying the wet-milled drug suspensions for dissolution and bioavailability enhancement. To this end, pullulan films, with xanthan gum (XG) as thickening agent and glycerin as plasticizer, were loaded with griseofulvin nanoparticles prepared by WSMM using pullulan in combination with sodium dodecyl sulfate (SDS) as an ionic stabilizer. The effects of drug loading and milling time on the particle size and suspension stability were investigated, as well as XG concentration and casting thickness on film properties and dissolution rate. The nanosuspensions prepared with pullulan-SDS combination were relatively stable over 7 days; hence, this combination was used for the film preparation. All pullulan-based strip films exhibited excellent content uniformity (most <3% RSD) despite containing only 0.3-1.3 mg drug, which was ensured by the use of precursor suspensions with >5000 cP viscosity. USP IV dissolution tests revealed fast/immediate drug release (t80 < 30 min) from films <120 µm thick. Thinner films, films with lower XG loading, or smaller drug particles led to faster drug dissolution, while drug loading had no discernible effect. Overall, these results suggest that pullulan may serve as an acceptable stabilizer for media milling in combination with surfactant as well as a fast-dissolving film former for the fast release of poorly water-soluble drug nanoparticles.

Is the combination of cellulosic polymers and anionic surfactants a good strategy for ensuring physical stability of BCS Class II drug nanosuspensions?

Ensuring the physical stability of drug nanosuspensions prepared via wet media milling has been a challenge for pharmaceutical scientists. The aim of this study is to assess the combined use of non-ionic cellulosic polymers and anionic surfactants in stabilizing multiple drug nanosuspensions. Particle size of five drugs, i.e. azodicarbonamide (AZD), fenofibrate (FNB), griseofulvin (GF), ibuprofen (IBU) and phenylbutazone (PB) was reduced separately in an aqueous solution of hydroxypropyl cellulose (HPC) with/without sodium dodecyl sulfate (SDS) via a stirred media mill. Laser diffraction, scanning electron microscopy, thermal analysis, rheometry and electrophoresis were used to evaluate the breakage kinetics, storage stability, electrostatic repulsion and stabilizer adsorption. Without SDS, drug particles exhibited aggregation to different extents; FNB and GF particles aggregated the most due to low zeta potential and insufficient steric stabilization. Although aggregation in all milled suspensions was reduced due to HPC-SDS combination, FNB and IBU showed notable growth during 7-day storage. It is concluded that the combination of non-ionic cellulosic polymers and anionic surfactants is generally viable for ensuring the physical stability of wet-milled drug nanosuspensions, provided that the surfactant concentration is optimized to mitigate the Ostwald ripening, whereas cellulosic polymers alone may provide stability for some drug suspensions.

An Intensified Vibratory Milling Process for Enhancing the Breakage Kinetics during the Preparation of Drug Nanosuspensions.

As a drug-sparing approach in early development, vibratory milling has been used for the preparation of nanosuspensions of poorly water-soluble drugs. The aim of this study was to intensify this process through a systematic increase in vibration intensity and bead loading with the optimal bead size for faster production. Griseofulvin, a poorly water-soluble drug, was wet-milled using yttrium-stabilized zirconia beads with sizes ranging from 50 to 1500 µm at low power density (0.87 W/g). Then, this process was intensified with the optimal bead size by sequentially increasing vibration intensity and bead loading. Additional experiments with several bead sizes were performed at high power density (16 W/g), and the results were compared to those from wet stirred media milling. Laser diffraction, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, and dissolution tests were used for characterization. Results for the low power density indicated 800 µm as the optimal bead size which led to a median size of 545 nm with more than 10% of the drug particles greater than 1.8 µm albeit the fastest breakage. An increase in either vibration intensity or bead loading resulted in faster breakage. The most intensified process led to 90% of the particles being smaller than 300 nm. At the high power intensity, 400 µm beads were optimal, which enhanced griseofulvin dissolution significantly and signified the importance of bead size in view of the power density. Only the optimally intensified vibratory milling led to a comparable nanosuspension to that prepared by the stirred media milling.

Spray drying of drug-swellable dispersant suspensions for preparation of fast-dissolving, high drug-loaded, surfactant-free nanocomposites.

Bioavailability of a poorly soluble drug can be improved by preparing a drug nanosuspension and subsequently drying it into nanocomposite microparticles (NCMPs). Unfortunately, drug nanoparticles aggregate during milling and drying, causing incomplete recovery and slow dissolution. The aim of this study is to investigate the impact of various classes of dispersants on drug dissolution from drug NCMPs, with the ultimate goal of enhancing the bioavailability of poorly water-soluble drugs via high drug nanoparticle loaded, surfactant-free NCMPs. Precursor suspensions of griseofulvin (GF, model drug) nanoparticles in the presence of various dispersants were prepared via wet stirred media milling and spray dried to form the NCMPs. Hydroxypropyl cellulose (HPC, polymer) alone and with sodium dodecyl sulfate (SDS, surfactant) was used as a base-line stabilizer/dispersant during milling. Two swellable crosslinked polymers, croscarmellose sodium (CCS) and sodium starch glycolate (SSG), and a conventional soluble matrix former, Mannitol, were used in addition to HPC. Besides being used as-received, CCS was also wet co-milled with GF for two different durations to examine the impact of CCS particle size. Laser diffraction, scanning electron microscopy, powder X-ray diffraction (XRD), UV spectroscopy, NCMP redispersion and dissolution tests were used for characterization. The results show that incorporation of CCS/SSG, preferably wet-milled to a wide particle size distribution, into the spray-dried NCMPs resulted in fast release and dispersion of drug nanoparticle clusters. The swellable dispersants were superior to Mannitol in dissolution enhancement, and could achieve fast release comparable to SDS, demonstrating the feasibility of spray drying to prepare high drug-loaded, surfactant-free nanocomposites.

Enhanced recovery and dissolution of griseofulvin nanoparticles from surfactant-free nanocomposite microparticles incorporating wet-milled swellable dispersants.

Nanocomposite microparticles (NCMPs) incorporating drug nanoparticles and wet-milled swellable dispersant particles were investigated as a surfactant-free drug delivery vehicle with the goal of enhancing the nanoparticle recovery and dissolution rate of poorly water-soluble drugs. Superdisintegrants were used as inexpensive, model, swellable dispersant particles by incorporating them into NCMP structure with or without wet-stirred media milling along with the drug. Suspensions of griseofulvin (GF, model drug) along with various dispersants produced by wet-milling were coated onto Pharmatose® to prepare NCMPs in a fluidized bed process. Hydroxypropyl cellulose (HPC, polymer) alone and with sodium dodecyl sulfate (SDS, surfactant) was used as base-line stabilizer/dispersant during milling. Croscarmellose sodium (CCS, superdisintegrant) and Mannitol were used as additional dispersants to prepare surfactant-free NCMPs. Nanoparticle recovery during redispersion and dissolution of the various GF-laden NCMPs were examined. Suspensions prepared by co-milling GF/HPC/CCS or milling GF/HPC/SDS were stable after 30 h of storage. After drying, due to its extensive swelling capacity, incorporation of wet-milled CCS in the NCMPs caused effective breakage of the NCMP structure and bursting of nanoparticle clusters, ultimately leading to fast recovery of the GF nanoparticles. Optimized wet co-milling and incorporation of CCS in NCMP structure led to superior dispersant performance over incorporation of unmilled CCS or physically mixed unmilled CCS with NCMPs. The enhanced redispersion correlated well with the fast GF dissolution from the NCMPs containing either CCS particles or SDS. Overall, swellable dispersant (CCS) particles, preferably in multimodal size distribution, enable a surfactant-free formulation for fast recovery/dissolution of the GF nanoparticles.

A Novel PBM for Nanomilling of Drugs in a Recirculating Wet Stirred Media Mill: Impacts of Batch Size, Flow Rate, and Back-Mixing.

We examined the evolution of fenofibrate (FNB, drug) particle size distribution (PSD) during the production of nanosuspensions via wet stirred media milling (WSMM) with a cell-based population balance model (PBM). Our objective was to elucidate the potential impacts of batch size, suspension volumetric flow rate, and imperfect mixing in a recirculating WSMM. Various specific breakage rate functions were fitted to experimental PSD data at baseline conditions assuming perfect mixing. Then, the best function was used to simulate the PSD evolution at various batch sizes and flow rates to validate the model. A novel function, which is a product of power-law and logistic functions, fitted the evolution the best, signifying the existence of a transition particle size commensurate with a grinding limit. Although larger batches yielded coarser and wider PSDs, the suspensions had identical PSDs when milled for the same effective milling time. The flow rate had an insignificant influence on the PSD. Furthermore, the imperfect mixing in the mill chamber was simulated by considering more than one cell and different back-mixing flow ratios. The effects were weak and restricted to the first few turnovers. These insights contribute to our understanding of recirculating WSMM, providing valuable guidance for process development.

Development of a Semi-Mechanistic Modeling Framework for Wet Bead Milling of Pharmaceutical Nanosuspensions.

This study aimed to develop a practical semi-mechanistic modeling framework to predict particle size evolution during wet bead milling of pharmaceutical nanosuspensions over a wide range of process conditions and milling scales. The model incorporates process parameters, formulation parameters, and equipment-specific parameters such as rotor speed, bead type, bead size, bead loading, active pharmaceutical ingredient (API) mass, temperature, API loading, maximum bead volume, blade diameter, distance between blade and wall, and an efficiency parameter. The characteristic particle size quantiles, i.e., x10, x50, and x90, were transformed to obtain a linear relationship with time, while the general functional form of the apparent breakage rate constant of this relationship was derived based on three models with different complexity levels. Model A, the most complex and general model, was derived directly from microhydrodynamics. Model B is a simpler model based on a power-law function of process parameters. Model C is the simplest model, which is the pre-calibrated version of Model B based on data collected from different mills across scales, formulations, and drug products. Being simple and computationally convenient, Model C is expected to reduce the amount of experimentation needed to develop and optimize the wet bead milling process and streamline scale-up and/or scale-out.

Atomic force microscope infrared spectroscopy of griseofulvin nanocrystals.

The goal of this work was to evaluate the ability of photothermal-induced resonance (PTIR) to measure the local infrared absorption spectra of crystalline organic drug nanoparticles embedded within solid matrices. Herein, the first reports of the chemical characterization of sub-100 nm organic crystals are described; infrared spectra of 90 nm griseofulvin particles were obtained, confirming the chemical resolution of PTIR beyond the diffraction limit. Additionally, particle size distributions via dynamic light scattering and PTIR image analysis were found to be similar, suggesting that the PTIR measurements are not significantly affected by inhomogeneous infrared absorptivity of this system. Thus as medical applications increasingly emphasize localized drug delivery via micro/nanoengineered structures, PTIR can be used to unambiguously chemically characterize drug formulations at these length scales.

Continuous production of drug nanoparticle suspensions via wet stirred media milling: a fresh look at the Rehbinder effect.

Nanoparticles of BCS Class II drugs are produced in wet stirred media mills operating in batch or recirculation mode with the goal of resolving the poor water-solubility issue. Scant information is available regarding the continuous production of drug nanoparticles via wet media milling. Griseofulvin and Naproxen were milled in both recirculation mode and multi-pass continuous mode to study the breakage dynamics and to determine the effects of suspension flow rate. The evolution of the median particle size was measured and described by an empirical breakage model. We found that these two operation modes could produce drug nanosuspensions with similar particle size distributions (PSDs). A reduced suspension flow rate slowed the breakage rate and led to a wider PSD and more differentiation between the two operation modes. The latter part of this study focused on the roles of stabilizers (hydroxypropyl cellulose and sodium lauryl sulfate) and elucidation of the so-called Rehbinder effect (reduction in particle strength due to adsorbed stabilizers such as polymers and surfactants). Milling the drugs in the absence of the stabilizers produced primary nanoparticles and their aggregates, while milling with the stabilizers produced smaller primary nanoparticles with minimal aggregation. Using laser diffraction, BET nitrogen adsorption, scanning electron microscopy imaging, and a microhydrodynamic analysis of milling, this study, for the first time, provides sufficient evidence for the existence of the Rehbinder effect during the milling of drugs. Not only do the polymers and surfactants allow proper stabilization of the nanoparticles in the suspensions, but they also do facilitate drug particle breakage.

Nanoseeded Desupersaturation and Dissolution Tests for Elucidating Supersaturation Maintenance in Amorphous Solid Dispersions.

The impact of residual drug crystals that are formed during the production and storage of amorphous solid dispersions (ASDs) has been studied using micron-sized seed crystals in solvent-shift (desupersaturation) and dissolution tests. This study examines the impacts of the seed size loading on the solution-mediated precipitation from griseofulvin ASDs. Nanoparticle crystals (nanoseeds) were used as a more realistic surrogate for residual crystals compared with conventional micron-sized seeds. ASDs of griseofulvin with Soluplus (Sol), Kollidon VA64 (VA64), and hydroxypropyl methyl cellulose (HPMC) were prepared by spray-drying. Nanoseeds produced by wet media milling were used in the dissolution and desupersaturation experiments. DLS, SEM, XRPD, and DSC were used for characterization. The results from the solvent-shift tests suggest that the drug nanoseeds led to a faster and higher extent of desupersaturation than the as-received micron-sized crystals and that the higher seed loading facilitated desupersaturation. Sol was the only effective nucleation inhibitor; the overall precipitation inhibition capability was ranked: Sol > HPMC > VA64. In the dissolution tests, only the Sol-based ASDs generated significant supersaturation, which decreased upon an increase in the nanoseed loading. This study has demonstrated the importance of using drug nanocrystals in lieu of conventional coarse crystals in desupersaturation and dissolution tests in ASD development.

Preparation and Characterization of Spray-Dried Hybrid Nanocrystal-Amorphous Solid Dispersions (HyNASDs) for Supersaturation Enhancement of a Slowly Crystallizing Drug.

We prepared hybrid nanocrystal-amorphous solid dispersions (HyNASDs) to examine their supersaturation capability in the release of a poorly soluble drug, itraconazole (ITZ), a slow crystallizer during dissolution. The HyNASD formulations included a polymer (HPC: hydroxypropyl cellulose, Sol: Soluplus, or VA64: Kollidon-VA64) and a surfactant (SDS: sodium dodecyl sulfate). Additionally, the dissolution performance of the HyNASDs and ASDs was compared. To this end, wet-milled aqueous nanosuspensions containing a 1:5 ITZ:polymer mass ratio with/without SDS as well as solutions of the same ratio without SDS in dichloromethane were spray-dried. XRPD-DSC confirmed that ASDs were formed upon spray drying the solution-based feeds, whereas HyNASDs (~5-30% amorphous) were formed with the nanosuspension-based feeds. SDS aided to stabilize the ITZ nanosuspensions and increase the amorphous content in the spray-dried powders. During dissolution, up to 850% and 790% relative supersaturation values were attained by HyNASDs with and without SDS, respectively. Due to the stronger molecular interaction between ITZ-Sol than ITZ-HPC/VA64 and micellar solubilization by Sol, Sol-based HyNASDs outperformed HPC/VA64-based HyNASDs. While the ASD formulations generated greater supersaturation values (≤1670%) than HyNASDs (≤790%), this extent of supersaturation from a largely nanocrystalline formulation (HyNASD) has not been achieved before. Overall, HyNASDs could boost drug release from nanoparticle-based formulations and may render them competitive to ASDs.

Do Mixtures of Beads with Different Sizes Improve Wet Stirred Media Milling of Drug Suspensions?

The impacts of bead sizes and bead mixtures on breakage kinetics, the number of milling cycles applied to prevent overheating, and power consumption during the nanomilling of drug (griseofulvin) suspensions were investigated from both an experimental and theoretical perspective. Narrowly sized zirconia beads with nominal sizes of 100, 200, and 400 µm and their half-and-half binary mixtures were used at 3000 and 4000 rpm with two bead loadings of 0.35 and 0.50. Particle size evolution was measured during the 3 h milling experiments using laser diffraction. An nth-order breakage model was fitted to the experimental median particle size evolution, and various microhydrodynamic parameters were calculated. In general, the beads and their mixtures with smaller median sizes achieved faster breakage. While the microhydrodynamic model explained the impacts of process parameters, it was limited in describing bead mixtures. For additional test runs performed, the kinetics model augmented with a decision tree model using process parameters outperformed that augmented with an elastic-net regression model using the microhydrodynamic parameters. The evaluation of the process merit scores suggests that the use of bead mixtures did not lead to notable process improvement; 100 µm beads generally outperformed bead mixtures and coarser beads in terms of fast breakage, low power consumption and heat generation, and low intermittent milling cycles.

Using USP I and USP IV for discriminating dissolution rates of nano- and microparticle-loaded pharmaceutical strip-films.

Recent interest in the development of drug particle-laden strip-films suggests the need for establishing standard regulatory tests for their dissolution. In this work, we consider the dissolution testing of griseofulvin (GF) particles, a poorly water-soluble compound, incorporated into a strip-film dosage form. The basket apparatus (USP I) and the flow-through cell dissolution apparatus (USP IV) were employed using 0.54% sodium dodecyl sulfate as the dissolution medium as per USP standard. Different rotational speeds and dissolution volumes were tested for the basket method while different cell patterns/strip-film position and dissolution media flow rate were tested using the flow-through cell dissolution method. The USP I was not able to discriminate dissolution of GF particles with respect to particle size. On the other hand, in the USP IV, GF nanoparticles incorporated in strip-films exhibited enhancement in dissolution rates and dissolution extent compared with GF microparticles incorporated in strip-films. Within the range of patterns and flow rates used, the optimal discrimination behavior was obtained when the strip-film was layered between glass beads and a flow rate of 16 ml/min was used. These results demonstrate the superior discriminatory power of the USP IV and suggest that it could be employed as a testing device in the development of strip-films containing drug nanoparticles.

Analysis of heat generation during the production of drug nanosuspensions in a wet stirred media mill.

Although heat is generated during the wet stirred media milling of drug suspensions, leading to notable temperature rise, a comprehensive analysis of heat generation does not exist. Hence, we investigated the impact of stirrer speed, bead loading, and bead size at three levels on the evolution of suspension temperature at the mill outlet during the milling of fenofibrate. The particle sizes and viscosities of the milled suspensions and power were measured. Our results suggest that stirrer speed had the most significant impact on the temperature increase, followed by bead loading and bead size. Both the time when the temperature reached 22 °C and the temperature at 5 min of milling were strongly correlated with the power. Assessing the impacts of the process parameters on the temperature rise, cycle time, power, and median particle size holistically, an optimal milling process was identified: 3000 rpm with 50% loading of 200 or 400 µm beads. A power number correlation was established to calculate power at any milling condition which determines the heat generation rate. Overall, this study indicated the importance of developing a good understanding of heat generation during nanomilling for development of a robust milling process especially for thermally labile drugs.

Predicting the Temperature Evolution during Nanomilling of Drug Suspensions via a Semi-Theoretical Lumped-Parameter Model.

Although temperature can significantly affect the stability and degradation of drug nanosuspensions, temperature evolution during the production of drug nanoparticles via wet stirred media milling, also known as nanomilling, has not been studied extensively. This study aims to establish both descriptive and predictive capabilities of a semi-theoretical lumped parameter model (LPM) for temperature evolution. In the experiments, the mill was operated at various stirrer speeds, bead loadings, and bead sizes, while the temperature evolution at the mill outlet was recorded. The LPM was formulated and fitted to the experimental temperature profiles in the training runs, and its parameters, i.e., the apparent heat generation rate Qgen and the apparent overall heat transfer coefficient times surface area UA, were estimated. For the test runs, these parameters were predicted as a function of the process parameters via a power law (PL) model and machine learning (ML) model. The LPM augmented with the PL and ML models was used to predict the temperature evolution in the test runs. The LPM predictions were also compared with those of an enthalpy balance model (EBM) developed recently. The LPM had a fitting capability with a root-mean-squared error (RMSE) lower than 0.9 °C, and a prediction capability, when augmented with the PL and ML models, with an RMSE lower than 4.1 and 2.1 °C, respectively. Overall, the LPM augmented with the PL model had both good descriptive and predictive capability, whereas the one with the ML model had a comparable predictive capability. Despite being simple, with two parameters and obviating the need for sophisticated numerical techniques for its solution, the semi-theoretical LPM generally predicts the temperature evolution similarly or slightly better than the EBM. Hence, this study has provided a validated, simple model for pharmaceutical engineers to simulate the temperature evolution during the nanomilling process, which will help to set proper process controls for thermally labile drugs.

Novel aspects of wet milling for the production of microsuspensions and nanosuspensions of poorly water-soluble drugs.

Micronization and nanoparticle production of poorly water-soluble drugs was investigated using single wet milling equipment operating in the attritor and stirred media modes. The drug particles in the median size range of 0.2?2??m were prepared by changing the milling mode and operating conditions of a Micros mill with a purpose of elucidating the dynamics of the wet milling process. It was determined that particle breakage due to mechanical stresses and aggregation due to insufficient stabilization are two competing mechanisms which together control the wet milling dynamics of the poorly water-soluble drugs. The study in the attritor mode using four different classes of stabilizers with six drugs indicated that steric stabilization worked better than electrostatic stabilization for the drugs studied. In addition, the existence of different minimum polymer concentrations for the stabilization of microsuspensions and nanosuspensions was indicated. The major role of a non-ionic polymer during the production of fine particles is its stabilization action through steric effects, and no experimental evidence was found to support the so-called Rehbinder effect. Periodic addition of the polymer as opposed to the addition of the polymer at the start of milling process was introduced as a novel processing method. This novel method of polymer addition provided effective stabilization and breakage of drug particles leading to a narrower and finer particle size distribution. Alternatively, it may allow shorter processing time and lower overall power consumption of the milling process for a desired particle size.

Impact of altered hydrophobicity and reduced agglomeration on dissolution of micronized poorly water-soluble drug powders after dry coating.

The impact of dry coating with hydrophobic or hydrophilic nano-silica at 25-100% surface area coverage on dissolution of micronized poorly water-soluble drugs was investigated by examining their agglomeration and surface hydrophobicity. Ibuprofen (20 µm and 10 µm) and griseofulvin (10 µm) were selected having differing solubility, hydrophobicity, and surface morphology. Characterization involved particle agglomeration via two dry dispersion methods, drug dissolution using the USP IV method, cohesion reduction through shear testing, and powder wettability via the modified Washburn method. Dry coating dramatically reduced the cohesion hence agglomerate size of both the coated ibuprofen particles, but less for griseofulvin, attributed to its surface morphology. For hydrophobic silica, agglomerate size reduction outweighed the adverse impact of increased surface hydrophobicity for ibuprofen. For griseofulvin, the agglomerate reduction was much lower, not able to overcome the effect of increased drug particle hydrophobicity with hydrophobic silica coating. Hydrophilic silica coating reduced hydrophobicity for all three drug powders, leading to the synergistic improvement in the dissolution along with agglomerate size reduction. Overall, the combined effect of the drug particle surface hydrophobicity and agglomerate size, represented by specific surface area, could explain the dissolution behavior of these poorly water-soluble drugs.

Kinetic and Microhydrodynamic Modeling of Fenofibrate Nanosuspension Production in a Wet Stirred Media Mill.

This study examined the impact of stirrer speed and bead material loading on fenofibrate particle breakage during wet stirred media milling (WSMM) via three kinetic models and a microhydrodynamic model. Evolution of median particle size was tracked via laser diffraction during WSMM operating at 3000-4000 rpm with 35-50% (v/v) concentration of polystyrene or zirconia beads. Additional experiments were performed at the center points of the above conditions, as well as outside the range of these conditions, in order to test the predictive capability of the models. First-order, nth-order, and warped-time kinetic models were fitted to the data. Main effects plots helped to visualize the influence of the milling variables on the breakage kinetics and microhydrodynamic parameters. A subset selection algorithm was used along with a multiple linear regression model (MLRM) to delineate how the breakage rate constant k was affected by the microhydrodynamic parameters. As a comparison, a purely empirical correlation for k was also developed in terms of the process/bead parameters. The nth-order model was found to be the best model to describe the temporal evolution; nearly second-order kinetics (n ≅ 2) was observed. When the process was operated at a higher stirrer speed and/or higher loading with zirconia beads as opposed to polystyrene beads, the breakage occurred faster. A statistically significant (p-value ≤ 0.01) MLRM of three microhydrodynamic parameters explained the variation in the breakage rate constant best (R2 ≥ 0.99). Not only do the models and the nth-order kinetic-microhydrodynamic correlation enable deeper process understanding toward developing a WSMM process with reduced cycle time, but they also provide good predictive capability, while outperforming the purely empirical correlation.