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A novel production method for inhalable cyclosporine A powders by confined liquid impinging jet precipitation
Aerosol Science 39 (2008) 500 – 509 www.elsevier.com/locate/jaerosci
A novel production method for inhalable cyclosporine A powders by confined liquid impinging jet precipitation Herbert Chioua , Hak-Kim Chana,∗ , Desmond Henga , Robert K. Prud’hommeb , Judy A. Raperc a Advanced Drug Delivery Group, Faculty of Pharmacy, The University of Sydney, NSW 2006, Australia b Department of Chemical Engineering, Princeton University, Princeton, NJ 08544, USA c Department of Chemical and Biological Engineering, University of Missouri, Rolla, MO 65409, USA
Received 26 November 2007; received in revised form 16 January 2008; accepted 13 February 2008
Abstract The aim of this work is to evaluate and optimise aerosol performance of precipitated cyclosporine A (CsA) powders as a model peptide for inhalation drug delivery. Confined liquid impinging jets (CLIJ) was used to precipitate CsA with stabilisers (lecithin and lactose), followed by spray drying to produce dry powders. Minimum concentrations of each stabiliser were determined from a matrix design of nine experimental conditions (i.e. 32 corresponding to 2 additives at 3 concentration levels). Suspensions of CsA particles of 180–700 nm were produced by CLIJ precipitation and powders comprising approximately 1 m agglomerates of CsA particles were obtained following spray drying. The internal structure of the agglomerates was not hollow. The aerosol performance of the CLIJ-spray dried powders was initially screened using a dry powder attachment on a laser diffractometer to identify the optimal CLIJ experimental conditions. The optimal aerosol performance was then confirmed using the Aeroliser 䉸 dry powder inhaler with a multi-stage liquid impinger operating at 60 and 100 L/min. The powder produced from spray drying of the suspension using CLIJ at 1% w/v lactose and 0.025% w/v lecithin showed the best dispersion behaviour and the corresponding aerosol performance shows a fine particle fraction of 54–56%. These results showed the potential of CLIJ precipitation with spray drying in the production of peptides for inhalation. 䉷 2008 Elsevier Ltd. All rights reserved. Keywords: Confined liquid impinging jet; Cyclosporine A (CsA); Inhalation drug delivery; Dry powder dispersion
1. Introduction Controlled delivery of drugs by inhalation to the lung using dry powder aerosols involves crucial production of the drug powder, in addition to formulation and inhaler device design (Chan, 2006). Conventional methods of crystallisation followed by jet milling to produce fine drug particles (< 5 m) required for inhalation delivery suffer many shortcomings (Brodka-Pfeiffer, Langguth, Grass, & Hausler, 2003). As a result, alternative methods have been or being developed, which include spray drying, spray freeze drying, wet milling, sonocrystallisation, supercritical fluid precipitation, and high gravity controlled precipitation. Confined liquid impinging jets (CLIJ) have been studied in the past for their heat transfer properties (Garimella & Rice, 1995), but recently they were used as a technique to produce particles in the ∗ Corresponding author. Tel.: +61 2 9351 3054; fax: +61 2 9351 4391.
E-mail address: [email protected] (H.-K. Chan). 0021-8502/$ - see front matter 䉷 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaerosci.2008.02.002
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sub-micron to nano range (Benet, Muhr, Plasari, & Rousseaux, 2002; Johnson & Prud’homme, 2003b, 2003c, 2003d). This technique involves rapid mixing of two liquid reactant streams within a confined mixing chamber without the use of any external mechanical stirrers (Johnson & Prud’homme, 2003a). More recently, CLIJ was applied to the precipitation of pharmaceutical compounds (Chiou, Chan, Prud’homme, & Raper, 2008; Wang, Gillian, & Kirwan, 2006). For pulmonary drug delivery using dry powders, drug particles need to be separated from the suspending liquid after the CLIJ precipitation process. Most separation techniques such as filtration or centrifugation followed by vacuum or oven drying are slow and tend to result in the formation of a hard cake which is difficult to disperse. In contrast, spray drying is a rapid drying process and has been shown to be suitable for sub-micron drug suspensions in producing inhalable dry powders (Chiou et al., 2007). Spray drying of the suspension droplets will lead to formation of spherical agglomerates of the primary particles (which can be of sub-micron or nano size). Particles in the latter size range would be highly cohesive, but larger sized agglomerates would be less so and, therefore, are easier to disperse into a dry powder aerosol. Once deposited in the lung, the agglomerates can dissociate into the smaller primary particles. For sparingly water soluble drugs, there is a potential benefit as the increased surface area of the small particles would enhance the dissolution rate and hence the bioavailability (Sham, Zhang, Finlay, Roa, & Lobenberg, 2004; Tsapis, Bennett, Jackson, Weitz, & Edwards, 2002). However, this will only be true if recovery of the primary particles does occur when the agglomerates come into contact with water or the lung fluid. The drug chosen for this work is a model peptide and a good example of a Biopharmaceutics Classification System Class II drug (low water solubility and high permeability) (Van De Waterbeemd, Lennernäs, & Artursson, 2003). Cyclosporine A (CsA) is an immunosuppressive agent used for the prevention of lung transplant rejections (Iacono et al., 2006), autoimmune disorders (Galeazzia, Bellisaia, Manganellia, Morozzia, & Sebastianib, 2006), and for the treatment of asthma (Underwood et al., 2001). CsA is soluble in hydrofluoroalkane propellants and used in pressured metered dose inhalers (pMDI) (Myrdal, Karlage, Stein, Brown, & Haynes, 2004). It has been shown by others that non-aqueous solutions of CsA could be spray dried to produce a liquid crystal form of CsA with mass median diameters of approximately 1.2 m, depending on the organic solvent and temperature used (Lechuga-Ballesteros et al., 2000). Recent work in co-spray freeze drying CsA and inulin to produce powders for inhalation with up to 50% w/w CsA loading was reported by Zijlstra et al. (2007) but so far there is no study on precipitating CsA particles containing practically pure (> 99%) drug for use in dry powder inhalers. Our preliminary work has shown that 300 nm CsA particles were obtained from CLIJ precipitation when the additive concentrations were not optimised (Chiou, Chan, et al., 2008). The additives employed were soy lecithin and dextrose monohydrate, which function to stabilise CsA particles in the suspension and act as a cryoprotectant for lyophilisation, respectively. Soy lecithin consists of phosphatidylcholine and other fatty acids, which are all surface active agents and are generally regarded as safe (GRAS). To prepare CsA for inhalation in the present study, dextrose monohydrate was replaced with lactose as it is widely used as carriers in dry powder inhalers. In addition, it is anticipated that the presence of a hydrophilic sugar (lactose) and surface active agent (lecithin) in the particles may facilitate wetting and the dissociation of the agglomerates into primary particles. The aim of this study is to evaluate and optimise the conditions for CLIJ precipitation followed by spray drying for the production of a model peptide suitable for dry powder inhalation drug delivery. 2. Methods and materials 2.1. Materials CsA was obtained from Fujian Kerui Pharmaceutical Co. Ltd., China. Ethanol (analytical grade) was supplied from Biolab, Australia, soy lecithin (Emultop䉸 ) from Degussa, USA, lactose (Lactochem䉸 ) from Borculo Domo Ingredients, The Netherlands, and plastic syringes (50 mL, 29.1 mm ID) from Livingstone, Australia. All were used as received. Deionised water (> 2 M cm resistivity at 25 ◦ C) was obtained from the Modulab Type II Deionisation System (Continental Water Systems, Sydney, Australia). 2.2. Methods 2.2.1. CLIJ mixing of CsA The CLIJ mixer set-up shown in Fig. 1 was previously described by Chiou, Chan, et al. (2008). In the present study, an ethanolic solution of CsA (10 mL, 100 mg/mL) was loaded into a syringe and an aqueous solution (10 mL)
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Fig. 1. The CLIJ mixer configuration.
containing soy lecithin and lactose as addictives, at concentrations indicated in the experimental matrix below, was loaded into a separate syringe. Each solution was dispensed by a syringe pump (PHD 2000, Harvard Apparatus, USA) at the maximum flow rate of 120 mL/min to simultaneously mix the two liquid streams within the CLIJ mixer. The resulting suspension was collected from the mixer outlet into a beaker that was magnetically stirred (500 ± 50 RPM) containing distilled water (100 mL) for quenching. From our preliminary study, at a CsA concentration of 100 mg/mL, the use of 0.025% w/v lecithin and 1% w/v lactose produced a fine CsA suspension (unpublished results). Based on this observation, an experimental matrix of nine conditions was designed by varying the lecithin and lactose content by up to two orders of magnitude difference for each additive (high, medium, and low levels, i.e. 0.025% w/v, 0.0025% w/v, and 0.00025% w/v for soy lecithin; 1% w/v, 0.1% w/v, and 0.01% w/v for lactose). The concentrations of the additives are relative to the 10 mL that they are dissolved in, where 1% w/v is equivalent to 100 mg in the final mixture. The samples in the experimental matrix were prepared by CLIJ precipitation, spray dried then analysed for their powder dispersion behaviour. 2.2.2. Spray drying of the CsA suspension Each quenched suspension of CsA was sonicated in an ultrasonic bath (FXP8M, Unisonics, Sydney, Australia) while being spray dried in a laboratory scale spray dryer (Mini Spray Dryer B-290, Buchi, Flawil, Switzerland) to obtain dry CsA powders using the following conditions: room humidity of 40 ± 3%, inlet and outlet temperatures of 120 and 55 ◦ C, respectively, aspiration rate of 100% (equivalent to 38 m3 /h), atomisation spray rate set at 65 mm on the rotameter (equivalent to 819 NL/h), and feed rate of 10% (i.e. 3.5 mL/min). 2.2.3. Particle crystallinity Crystallinity of the dry CsA powders and the initial material was assessed by X-ray powder diffraction (XRD, D5000, Siemens, Germany) at room temperature using Cu K radiation at 30 mA and 40 kV, with an angular increment of 0.05◦ /s and count time of 2 s from 2 of 3–40◦ . 2.2.4. Electron microscopy and focused-ion-beam milling Morphology of the CsA powders was examined by high-resolution scanning electron microscopy (SEM, JSM 6000F, Joel, Japan) operating at 5 kV and the sample was sputter coated with a 50 nm layer of platinum to improve thermal conductivity and prevent sample melting during measurement. Focused-ion-beam (FIB) milling of the CsA agglomerates (produced with 0.025% w/v lecithin and 1% w/v lactose) was performed in an FIB/scanning electron microscope dual beam system (Quanta 200 3D, FEI, USA) using a similar procedure described previously, but without the cleaning step (Heng et al., 2007). The CsA powder was mounted onto a 100-mesh transmission electron microscopy grid (GCu100, ProSciTech, Australia) and coated with a 50 nm layer of gold. Vertical cutting of the sample was performed at a stage tilt of 52◦ with an accelerating voltage of 10 kV and a beam current of 16 pA. Milling times was kept under 5 min. The milled agglomerates were later examined using the high-resolution SEM (JSM 6000F, Joel, Japan) at 3 kV, as the milled surface is not coated, and tilted at 30◦ to examine the cut surface. 2.2.5. Particle size determination and powder dispersion A dry powder feeder (Sirocco, Malvern, Worcs, UK) connected to a laser diffractometer (Mastersizer 2000, Malvern, Worcs, UK) allowed a rapid means to screen the dispersion behaviour of the processed powders to help identify the optimal CLIJ experimental conditions. The change in the volume-weighted particle size distribution (PSD) of the
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Fig. 2. Schematic diagram of the dry powder feeder.
CLIJ-spray dried CsA agglomerates as a function of the dispersing air pressure (i.e. a pressure titration) was determined using the refractive indices of CsA (1.578 and 0.100 for the real and imaginary components, respectively) and the dispersing air (1.000). The pressure titration study was performed at various air pressures (between 0.5 and 4 bars) and the resulting PSD was measured until the maximum pressure was reached or the powder was apparently fully dispersed (as shown by reaching a plateau of the particle size in the titration curve). During the measurement, the sample powder (5–10 mg) was shaken from a vibrating sample tray where the sample was then blown by compressed air, introduced at a set pressure, against and around a bend then across the lens for the PSD measurement (Fig. 2). Once identified in the laser-diffraction measurement, the optimal aerosol performance of the powders was then confirmed on a commercial inhaler. 2.2.6. Aerosol performance While the dry powder feeder can indicate the relative product performance among the samples, it is not an inhaler, suitable for patient use. As the aim of this study is to produce CsA for dry powder inhalation, the aerosol dispersion behaviour of the best performing powder was realistically assessed using an Aeroliser 䉸 (Novartis Pharmaceuticals, Australia) coupled through an USP stainless steel throat to a multi-stage liquid impinger (MSLI, Copley, UK), operating at 60 and 100 L/min. Powder (10.0±0.5 mg) was filled into hydroxypropyl methylcellulose capsules (size 3, Capsugel䉸 , USA) and single capsules were used in each experiment. Measurements were performed in duplicate. CsA deposited at different locations was assayed by UV spectrophotometry (U-2000, Hitachi, Japan) at 214 nm. A linear calibration curve of CsA in ethanol was constructed in the concentration range of 5.40 g/mL [concentration (g/mL)=38.896× absorbance + 1.851; R 2 = 0.9875]. Fine particle fraction (FPF) is defined as the mass fraction of drug particles smaller than 5 m in the aerosol cloud (interpolated from the mass of drug collected from stages 3, 4 and filter) relative to the total mass recovered. 2.2.7. Visualisation of agglomerate dissociation Dissociation of the primary particles from CsA agglomerates was visualised under an optical microscope (BX60, Olympus, Japan), connected to a digital microscope camera (AxioCam, Carl Zeiss, Germany) for image recording (AxioVision V4.6.1.0., Carl Zeiss, Germany). CLIJ-spray dried CsA powder (0.025% w/v lecithin and 1% w/v lactose) sandwiched between a glass microscope slide and cover slip was initially imaged. The cover slip was then removed and a drop of deionised water was introduced directly to the sample. The slip was immediately replaced and further images of the sample were taken. 3. Results and discussions 3.1. Powder properties—crystallinity, particle size, and morphology All CsA powders from the CLIJ precipitation process followed by spray drying have a similar X-ray diffraction pattern compared with the initial material (Fig. 3), all appearing to be amorphous. While it is possible that they are thermotropic liquid crystals (Lechuga-Ballesteros, Abdul-Fattah, Stevenson, & Bennett, 2003), it is unlikely since optical birefringence was absent using polarising microscopy. The contribution of the two additives to crystallinity is minimal considering the amounts used. The primary particles of the CLIJ precipitated CsA were spherical and the shape was maintained in the agglomerates after spray drying (Figs. 4A and B). Depending on the concentration of the additives used, the CsA primary particle size in the agglomerates ranges between 180 and 700 nm, as observed by SEM images (Figs. 4A and B), whereas the agglomerates are of approximately 1 m. As shown in the SEM images
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Fig. 3. X-ray diffraction patterns of CsA powders (
initial material, · · · CLIJ mixing with 1% w/v lactose and 0.025% w/v lecithin).
Fig. 4. SEM images of CsA powder after (A) spray drying of the suspension produced with 0.025% w/v lecithin with 1% w/v lactose and (B) the same powder sectioned perpendicular to the supporting plane by FIB with the plane tilted to show more of the cut face.
after sectioning by the FIB milling (Figs. 4C and D), these agglomerates are not hollow, hence they are not similar to other spray dried nanoparticle agglomerates such as Trojan particles (Tsapis et al., 2002). The sectioned faces reveal that they appear to be typical agglomerates rather than hollow particles with shell composed of agglomerates. 3.2. Dry powder dispersion of CsA product The size–pressure titration profiles (Fig. 5) for all of the nine samples are grouped by the lactose content (low, medium, and high). All samples show a decrease in the apparent agglomerate size of the bulk powder with increasing dispersing air pressure, and at the lower pressures this is the smallest for the sample containing the highest level of lactose and lecithin. At sufficiently high pressures the samples could be dispersed to aerosols of a similar volume median diameter of around 1 m, regardless of the additive concentrations. Each profile can be fitted to a simple power law, expressed as volume median diameter (VMD) = a + b × disperser pressurec .
(1)
Expression (1) is an empirical equation linking the VMD of the powder agglomerates to various curve-fitting parameters, where parameter “a” is related to the minimal agglomerate size that is achievable in the dry powder disperser, “b” to the extent of agglomerate size change during dispersion, and “c” to how readily the agglomerates break up on increasing disperser pressure. A small VMD would require a small value of a, b, and/or c. The effect of the additives on these
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Fig. 5. Pressure titration profile of the spray dried CLIJ processed powders at different lecithin concentrations ( – – – 0.025% w/v) and low (A, 0.01% w/v), medium (B, 0.1% w/v), and high (C, 1% w/v) levels of lactose.
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0.00025% w/v, · · · 0.0025% w/v,
parameters is shown as contour plots for which the additive concentrations for optimal aerosolisation (i.e. resulting in the smallest VMD) were identified (Fig. 6). As reflected by the parameter a values (Fig. 6A), the agglomerate size decreased only slightly to 0.7 m from the original agglomerate size of around 1 m, indicating that the dry powder feeder did not fully disperse the agglomerates into the primary particles of 180–700 nm in size (Fig. 4) at the highest disperser pressure available. The parameters b and c describe the extent, and the rate, of change in size of the agglomerates, respectively. Hence, they are related to the force required to break the agglomerates which, in turn, determines the dispersion performance. Below 0.1% w/v lactose, parameter b ranges between 1.0 and 1.4 m/bar, and it depends predominantly on the concentration of lecithin rather than lactose. Above the critical concentration of 0.1% lactose, the value of parameter b reduces to 0.6 m/bar, and the change is no longer dependent on the lecithin concentration (Fig. 6B). According to Eq. (1), a reduced b value would mean a smaller VMD for the agglomerates. Overall, higher concentrations of lactose reduce the b value, which helps dispersion particularly at lower disperser pressures. The parameter c is influenced by both the lecithin and lactose concentrations (Fig. 6C). It is always negative as the VMD is decreasing with increasing air pressure. High concentrations of both lactose and lecithin favour a value close to zero for c, indicating that the agglomerates are easier to disperse. The results suggest that the presence of the additives at a high concentration may coat the particles sufficiently to reduce the inter-particulate forces required to separate the agglomerates. A value of zero for c shows that the VMD is independent of disperser pressure. While both lactose and lecithin contribute to the stability of the CsA particles during spray drying, they operate by different mechanisms. Lecithin, as an amphiphilic molecule accumulates on the CsA particle surface during the initial formation step in the impinging jet mixing (Johnson & Prud’homme, 2003c). This surface layer control particle aggregation of the primary particles in the initial solution stage. During spray drying the primary particles are concentrated as water evaporates. The polar component moieties of the lecithin molecule provide a steric and electrostatic barrier to prevent contact between particles and fusion. A fused CsA aggregate would both be too large in size, would not readily fragment down to the desired aerodynamic size during dispersion, and would not readily dissociate back to the primary
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Fig. 6. Contour plots of parameters (A) “a”, (B) “b”, and (C) “c” against lecithin and lactose concentrations.
particle size when re-hydrated. Hence, the lecithin mode of action is as an interfacially active surfactant. In contrast, lactose is completely hydrophilic and has no tendency to interact with the CsA particle surface so it has little effect during particle formation in the wet state. However, during drying, the concentration of the lactose causes the aqueous phase to first increase in viscosity and finally form a solid amorphous phase with a sticky nature (Chiou & Langrish, 2007). The lactose physically immobilizes the CsA primary particles either embedded in this amorphous phase or stuck together. Presumably, the aerosol aggregate size is controlled by bridges and interfaces between hydrophilic lactose solid regions and hydrophobic CsA surfaces. The aerosol fragmentation of these aggregates would depend, in rather complicated ways on the relative volume fractions of the components and their interfacial adhesion. During re-hydration the soluble lactose can dissolve and the CsA particles return to their original size prior to spray drying. Both lecithin and lactose play a role in the spray drying of the CsA—the former chemically based and the latter steric in nature. The size–pressure titration profiles show that powders with a medium level of lecithin (0.0025% w/v) are less dispersible compared with the low or high levels (Fig. 5). This could be due to the difference in the extent of surface coverage of CsA particles by lecithin (Fig. 7). At low surface coverage, deagglomeration is dominated by the surface forces between the hydrophobic CsA particles. As lactose concentration is increased, so is the surface coverage and a monolayer may actually form at the medium additive level. Since the lecithin molecules will adsorb on the CsA surface via hydrophobic interactions, the polar groups of lecithin will be sticking out making the CsA surface more polar, which may contribute to the decreased dispersibility of the CsA particles. At a high lecithin level when the surface is covered with excess additives (i.e. multilayer), deagglomeration depends mainly on interactions between the additives. The excess lecithin molecules will initially interact via their hydrophilic groups with those in the monolayer, resulting in the polar groups exposing to the aqueous environment. However, the situation can be complex, as the structure will collapse when water is removed in drying and hence the interactions can change. The resulting CsA surface is
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Fig. 7. Surface coverage of lecithin on CsA particles.
likely to be hydrophobic, as suggested by the similarity between the titration profiles of the low and high levels of lecithin. In summary, whereas high lactose level alone reduces the values of parameter b and high lecithin level reduces the parameter a, high levels of both lecithin and lactose reduce the magnitude of parameter c. These results confirm that CLIJ precipitation of CsA in the presence of 0.025% w/v lecithin and 1% w/v lactose followed by spray drying could produce a powder with good aerosol dispersion performance. 3.3. Aerosol performance While the dry powder feeder is capable of comparing the intrinsic aerosolisation behaviour of the various powders, it is not suitable as an inhaler for patient use. The CsA powder determined by the dry powder disperser as the optimum was thus subsequently dispersed using a commercial dry powder inhaler, the Aeroliser 䉸 . The FPF of powder less than 5 m was found to be 54.2 ± 2.2% and 56.8 ± 0.02% at 60 and 100 L/min, respectively, with the majority of the powder deposited on stage 3 and below (Fig. 8). The FPF relative to the emitted dose are 66.2 ± 2.1% and 78.0 ± 0.1% at 60 and 100 L/min, respectively. Minimal throat deposition (4–5%) suggests the agglomerates that exit the inhalation device are small, reflecting the results obtained from the dry powder feeder (Fig. 5C). Based on a whole lung deposition of 60–70% relative to the FPF of powder less than 5 m (Clark & Borgstrom, 2002), the 10 mg of powder loaded in the capsule for dispersion would translate to between 3.3 and 3.8 mg of CsA deposited in the lung. This is about the minimum amount required (5 mg) to improve the pulmonary function of lung transplant patients with chronic rejection (Corcoran et al., 2004). This amount could be achieved with two capsules or a higher loading in a single capsule, compared with a metered dose inhaler formulation requiring five actuations to achieve approximately half the minimum amount required (Myrdal et al., 2004). 3.4. Dissociation of CsA agglomerates When the CLIJ-spray dried CsA powder (containing 0.025% w/v lecithin and 1% w/v lactose) came in contact with water, the agglomerates were observed to dissociate with the resulting smaller fragments or primary particles in size below 1 m (Fig. 9). The dissociation can readily be attributed to dissolution of the water soluble additives in the agglomerates. It must be noted that the purpose of the experiment was not to simulate what would happen in the lungs (which necessitates a separate in vivo study). While deionised water did not mimic the lung lining fluids, the result showed that the primary particles of CsA did not fuse together and become undissociable during the precipitation–spray drying process. Based on the in vitro results, we speculate that the agglomerates will dissociate into the nanoparticles followed by dissolution in the lungs. Despite the presence of the hydrophobic portion of the phospholipids on the
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Fig. 8. Percentage of mass deposited on each stage of multi-stage liquid impinger. The cutoff diameters of stages 1, 2, 3, and 4 calibrated at 60 L/min √ (white) are 13.0, 6.8, 3.1, and 1.7 m; at 100 L/min (grey) the cutoff diameters were calculated using D50 calc = D50 calc Qcalib /Qcalib (where D50 and Q are the cutoff diameter and flow rate, respectively, for the calibrated (calib) and calculated (calc) values) to be 10.1, 5.3, 2.4, and 1.3 m.
Fig. 9. Dissociation of CsA agglomerates, prior to (A) and after the addition of water (B) under optical microscopy.
particle surface, lung surfactants in the airways may help facilitate the dissociation process. The study will continue in the future to include such in vivo work. 4. Conclusion In conclusion, CLIJ precipitation coupled with spray drying is suitable for producing inhalable peptides. Strong aerosol performance of the CsA powder is achieved without the use of large carrier particles but with minimal concentrations of additives in the precipitation process. The required clinical dosage to improve the pulmonary function of lung transplant patients could potentially be achieved with two doses. Pressure titration was found to be a quick method to determine the suitability of dry powders for inhalation drug delivery. Acknowledgements This work was supported by a grant from the Australian Research Council (DP 0451940). DH is a recipient of the Australian Postgraduate Award (Industry). One of the authors (J.A.R) is located at the NSF. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. RKP acknowledges financial support from the NSF NIRT grant on Nanoparticle Formation and the Bill and Melinda Gates Foundation grant to Harvard University.
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References Benet, N., Muhr, H., Plasari, E., & Rousseaux, J. M. (2002). New technologies for the precipitation of solid particles with controlled properties. Powder Technology, 128, 93–98. Brodka-Pfeiffer, K., Langguth, P., Grass, P., & Hausler, H. (2003). Influence of mechanical activation on the physical stability of salbutamol sulphate. European Journal of Pharmaceutics and Biopharmaceutics, 56, 393–400. Chan, H.-K. (2006). Dry powder aerosol drug delivery—Opportunities for colloid and surface scientists. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 284–285, 50–55. Chiou, D., & Langrish, T. A. G. (2007). Crystallization of amorphous components in spray-dried powders. Drying Technology, 25, 1427–1435. Chiou, H., Chan, H.-K., Prud’homme, R. K., & Raper, J. A. (2008). Evaluation on the use of confined liquid impinging jets for synthesis of nano-drug particles. Drug Development and Industrial Pharmacy, 34, 59–64. Chiou, H., Li, L., Hu, T., Chan, H.-K., Chen, J.-F., & Yun, J. (2007). Production of salbutamol sulfate for inhalation by high-gravity controlled antisolvent precipitation. International Journal of Pharmaceutics, 331, 93–98. Clark, A., & Borgstrom, L. (2002). In vitro testing of pharmaceutical aerosols and predicting lung deposition from in vitro measurements. Lung Biology in Health and Disease, 162, 105–142. Corcoran, T. E., Smaldone, G. C., Dauber, J. H., Smith, D. A., Mccurry, K. R., Burckart, G. J. et al. (2004). Preservation of post-transplant lung function with aerosol cyclosporin. European Respiratory Journal, 23, 378–383. Galeazzia, M., Bellisaia, F., Manganellia, S., Morozzia, G., & Sebastianib, G. D. (2006). Cyclosporine A for the treatment of autoimmune disorders in HCV infected patients. Autoimmunity Reviews, 5, 493–498. Garimella, S. V., & Rice, R. A. (1995). Confined and submerged liquid jet impingement heat transfer. Journal of Heat Transfer, 117, 871–877. Heng, D., Tang, P., Cairney, J. M., Chan, H.-K., Cutler, D. J., Salama, R. et al. (2007). Focused-ion-beam milling: A novel approach to probing the interior of particles used for inhalation aerosols. Pharmaceutical Research, 24, 1608–1617. Iacono, A. T., Johnson, B. A., Grgurich, W. F., Youssef, J. G., Corcoran, T. E., Seiler, D. A. et al. (2006). A randomized trial of inhaled cyclosporine in lung-transplant recipients. The New England Journal of Medicine, 354, 141–150. Johnson, B. K., & Prud’homme, R. K. (2003a). Chemical processing and micromixing in confined impinging jets. AIChE Journal, 49, 2264–2282. Johnson, B. K., & Prud’homme, R. K. (2003b). Engineering the direct precipitation of stabilized organic and block copolymer nanoparticles as unique composites. Polymeric Materials Science and Engineering, 89, 744–745. Johnson, B. K., & Prud’homme, R. K. (2003c). Flash nanoprecipitation of organic actives and block copolymers using a confined impinging jets mixer. Australian Journal of Chemistry, 56, 1021–1024. Johnson, B. K., & Prud’homme, R. K. (2003d). Mechanism for rapid self-assembly of block copolymer nanoparticles. Physical Review Letters 91, 118302/118301–118302/118304. Lechuga-Ballesteros, D., Abdul-Fattah, A., Stevenson, C. L., & Bennett, D. B. (2003). Properties and stability of a liquid crystal form of cyclosporine—The first reported naturally occurring peptide that exists as a thermotropic liquid crystal. Journal of Pharmaceutical Sciences, 92, 1821–1831. Lechuga-Ballesteros, D., Bennett, D., Cabot, K., Farinas, K., Gong, D., Hastedt, J. et al. (2000). Aerosol drug development of a spray dried liquid crystalline formulation of cyclosporine. In: R. N. Dalby, P. Byron, S. J. Farr, & J. Peart (Eds.), Respiratory drug delivery VII Tarpon Springs, Florida: Serentec Press. Myrdal, P. B., Karlage, K. L., Stein, S. W., Brown, B. A., & Haynes, A. (2004). Optimized dose delivery of the peptide cyclosporine using hydrofluoroalkane-based metered dose inhalers. Journal of Pharmaceutical Sciences, 93, 1054–1061. Sham, J. O. H., Zhang, Y., Finlay, W. H., Roa, W. H., & Lobenberg, R. (2004). Formulation and characterization of spray-dried powders containing nanoparticles for aerosol delivery to the lung. International Journal of Pharmaceutics, 269, 457–467. Tsapis, N., Bennett, D., Jackson, B., Weitz, D. A., & Edwards, D. A. (2002). Trojan particles: Large porous carriers of nanoparticles for drug delivery. Proceedings of the National Academy of Sciences of the United States of America 99, 12001–12005. Underwood, S. L., Mcmillan, S., Reeves, R., Hunt, J., Brealey, C. J., Webber, S. et al. (2001). Effects of cyclosporin A administered into the airways against antigen-induced airway inflammation and hyperreactivity in the rat. European Journal of Pharmacology, 420, 165–172. (2003). In: H. Van De Waterbeemd, H. Lennernäs, & P. Artursson (Eds.), Drug bioavailability: Estimation of solubility, permeability, absorption and bioavailability Weinheim, Germany: Wiley-VCH. Wang, X., Gillian, J. M., & Kirwan, D. J. (2006). Quasi-emulsion precipitation of pharmaceuticals. 1. Conditions for formation and crystal nucleation and growth behavior. Crystal Growth & Design, 6, 2214–2227. Zijlstra, G. S., Rijkeboer, M., Van Drooge, D. J., Sutter, M., Jiskoot, W., Van De Weert, M. et al. (2007). Characterization of a cyclosporine solid dispersion for inhalation. AAPS Journal, 9, E190–E199.
A novel production method for inhalable cyclosporine A powders by confined liquid impinging jet precipitation Herbert Chioua , Hak-Kim Chana,∗ , Desmond Henga , Robert K. Prud’hommeb , Judy A. Raperc a Advanced Drug Delivery Group, Faculty of Pharmacy, The University of Sydney, NSW 2006, Australia b Department of Chemical Engineering, Princeton University, Princeton, NJ 08544, USA c Department of Chemical and Biological Engineering, University of Missouri, Rolla, MO 65409, USA
Received 26 November 2007; received in revised form 16 January 2008; accepted 13 February 2008
Abstract The aim of this work is to evaluate and optimise aerosol performance of precipitated cyclosporine A (CsA) powders as a model peptide for inhalation drug delivery. Confined liquid impinging jets (CLIJ) was used to precipitate CsA with stabilisers (lecithin and lactose), followed by spray drying to produce dry powders. Minimum concentrations of each stabiliser were determined from a matrix design of nine experimental conditions (i.e. 32 corresponding to 2 additives at 3 concentration levels). Suspensions of CsA particles of 180–700 nm were produced by CLIJ precipitation and powders comprising approximately 1 m agglomerates of CsA particles were obtained following spray drying. The internal structure of the agglomerates was not hollow. The aerosol performance of the CLIJ-spray dried powders was initially screened using a dry powder attachment on a laser diffractometer to identify the optimal CLIJ experimental conditions. The optimal aerosol performance was then confirmed using the Aeroliser 䉸 dry powder inhaler with a multi-stage liquid impinger operating at 60 and 100 L/min. The powder produced from spray drying of the suspension using CLIJ at 1% w/v lactose and 0.025% w/v lecithin showed the best dispersion behaviour and the corresponding aerosol performance shows a fine particle fraction of 54–56%. These results showed the potential of CLIJ precipitation with spray drying in the production of peptides for inhalation. 䉷 2008 Elsevier Ltd. All rights reserved. Keywords: Confined liquid impinging jet; Cyclosporine A (CsA); Inhalation drug delivery; Dry powder dispersion
1. Introduction Controlled delivery of drugs by inhalation to the lung using dry powder aerosols involves crucial production of the drug powder, in addition to formulation and inhaler device design (Chan, 2006). Conventional methods of crystallisation followed by jet milling to produce fine drug particles (< 5 m) required for inhalation delivery suffer many shortcomings (Brodka-Pfeiffer, Langguth, Grass, & Hausler, 2003). As a result, alternative methods have been or being developed, which include spray drying, spray freeze drying, wet milling, sonocrystallisation, supercritical fluid precipitation, and high gravity controlled precipitation. Confined liquid impinging jets (CLIJ) have been studied in the past for their heat transfer properties (Garimella & Rice, 1995), but recently they were used as a technique to produce particles in the ∗ Corresponding author. Tel.: +61 2 9351 3054; fax: +61 2 9351 4391.
E-mail address: [email protected] (H.-K. Chan). 0021-8502/$ - see front matter 䉷 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaerosci.2008.02.002
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sub-micron to nano range (Benet, Muhr, Plasari, & Rousseaux, 2002; Johnson & Prud’homme, 2003b, 2003c, 2003d). This technique involves rapid mixing of two liquid reactant streams within a confined mixing chamber without the use of any external mechanical stirrers (Johnson & Prud’homme, 2003a). More recently, CLIJ was applied to the precipitation of pharmaceutical compounds (Chiou, Chan, Prud’homme, & Raper, 2008; Wang, Gillian, & Kirwan, 2006). For pulmonary drug delivery using dry powders, drug particles need to be separated from the suspending liquid after the CLIJ precipitation process. Most separation techniques such as filtration or centrifugation followed by vacuum or oven drying are slow and tend to result in the formation of a hard cake which is difficult to disperse. In contrast, spray drying is a rapid drying process and has been shown to be suitable for sub-micron drug suspensions in producing inhalable dry powders (Chiou et al., 2007). Spray drying of the suspension droplets will lead to formation of spherical agglomerates of the primary particles (which can be of sub-micron or nano size). Particles in the latter size range would be highly cohesive, but larger sized agglomerates would be less so and, therefore, are easier to disperse into a dry powder aerosol. Once deposited in the lung, the agglomerates can dissociate into the smaller primary particles. For sparingly water soluble drugs, there is a potential benefit as the increased surface area of the small particles would enhance the dissolution rate and hence the bioavailability (Sham, Zhang, Finlay, Roa, & Lobenberg, 2004; Tsapis, Bennett, Jackson, Weitz, & Edwards, 2002). However, this will only be true if recovery of the primary particles does occur when the agglomerates come into contact with water or the lung fluid. The drug chosen for this work is a model peptide and a good example of a Biopharmaceutics Classification System Class II drug (low water solubility and high permeability) (Van De Waterbeemd, Lennernäs, & Artursson, 2003). Cyclosporine A (CsA) is an immunosuppressive agent used for the prevention of lung transplant rejections (Iacono et al., 2006), autoimmune disorders (Galeazzia, Bellisaia, Manganellia, Morozzia, & Sebastianib, 2006), and for the treatment of asthma (Underwood et al., 2001). CsA is soluble in hydrofluoroalkane propellants and used in pressured metered dose inhalers (pMDI) (Myrdal, Karlage, Stein, Brown, & Haynes, 2004). It has been shown by others that non-aqueous solutions of CsA could be spray dried to produce a liquid crystal form of CsA with mass median diameters of approximately 1.2 m, depending on the organic solvent and temperature used (Lechuga-Ballesteros et al., 2000). Recent work in co-spray freeze drying CsA and inulin to produce powders for inhalation with up to 50% w/w CsA loading was reported by Zijlstra et al. (2007) but so far there is no study on precipitating CsA particles containing practically pure (> 99%) drug for use in dry powder inhalers. Our preliminary work has shown that 300 nm CsA particles were obtained from CLIJ precipitation when the additive concentrations were not optimised (Chiou, Chan, et al., 2008). The additives employed were soy lecithin and dextrose monohydrate, which function to stabilise CsA particles in the suspension and act as a cryoprotectant for lyophilisation, respectively. Soy lecithin consists of phosphatidylcholine and other fatty acids, which are all surface active agents and are generally regarded as safe (GRAS). To prepare CsA for inhalation in the present study, dextrose monohydrate was replaced with lactose as it is widely used as carriers in dry powder inhalers. In addition, it is anticipated that the presence of a hydrophilic sugar (lactose) and surface active agent (lecithin) in the particles may facilitate wetting and the dissociation of the agglomerates into primary particles. The aim of this study is to evaluate and optimise the conditions for CLIJ precipitation followed by spray drying for the production of a model peptide suitable for dry powder inhalation drug delivery. 2. Methods and materials 2.1. Materials CsA was obtained from Fujian Kerui Pharmaceutical Co. Ltd., China. Ethanol (analytical grade) was supplied from Biolab, Australia, soy lecithin (Emultop䉸 ) from Degussa, USA, lactose (Lactochem䉸 ) from Borculo Domo Ingredients, The Netherlands, and plastic syringes (50 mL, 29.1 mm ID) from Livingstone, Australia. All were used as received. Deionised water (> 2 M cm resistivity at 25 ◦ C) was obtained from the Modulab Type II Deionisation System (Continental Water Systems, Sydney, Australia). 2.2. Methods 2.2.1. CLIJ mixing of CsA The CLIJ mixer set-up shown in Fig. 1 was previously described by Chiou, Chan, et al. (2008). In the present study, an ethanolic solution of CsA (10 mL, 100 mg/mL) was loaded into a syringe and an aqueous solution (10 mL)
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Fig. 1. The CLIJ mixer configuration.
containing soy lecithin and lactose as addictives, at concentrations indicated in the experimental matrix below, was loaded into a separate syringe. Each solution was dispensed by a syringe pump (PHD 2000, Harvard Apparatus, USA) at the maximum flow rate of 120 mL/min to simultaneously mix the two liquid streams within the CLIJ mixer. The resulting suspension was collected from the mixer outlet into a beaker that was magnetically stirred (500 ± 50 RPM) containing distilled water (100 mL) for quenching. From our preliminary study, at a CsA concentration of 100 mg/mL, the use of 0.025% w/v lecithin and 1% w/v lactose produced a fine CsA suspension (unpublished results). Based on this observation, an experimental matrix of nine conditions was designed by varying the lecithin and lactose content by up to two orders of magnitude difference for each additive (high, medium, and low levels, i.e. 0.025% w/v, 0.0025% w/v, and 0.00025% w/v for soy lecithin; 1% w/v, 0.1% w/v, and 0.01% w/v for lactose). The concentrations of the additives are relative to the 10 mL that they are dissolved in, where 1% w/v is equivalent to 100 mg in the final mixture. The samples in the experimental matrix were prepared by CLIJ precipitation, spray dried then analysed for their powder dispersion behaviour. 2.2.2. Spray drying of the CsA suspension Each quenched suspension of CsA was sonicated in an ultrasonic bath (FXP8M, Unisonics, Sydney, Australia) while being spray dried in a laboratory scale spray dryer (Mini Spray Dryer B-290, Buchi, Flawil, Switzerland) to obtain dry CsA powders using the following conditions: room humidity of 40 ± 3%, inlet and outlet temperatures of 120 and 55 ◦ C, respectively, aspiration rate of 100% (equivalent to 38 m3 /h), atomisation spray rate set at 65 mm on the rotameter (equivalent to 819 NL/h), and feed rate of 10% (i.e. 3.5 mL/min). 2.2.3. Particle crystallinity Crystallinity of the dry CsA powders and the initial material was assessed by X-ray powder diffraction (XRD, D5000, Siemens, Germany) at room temperature using Cu K radiation at 30 mA and 40 kV, with an angular increment of 0.05◦ /s and count time of 2 s from 2 of 3–40◦ . 2.2.4. Electron microscopy and focused-ion-beam milling Morphology of the CsA powders was examined by high-resolution scanning electron microscopy (SEM, JSM 6000F, Joel, Japan) operating at 5 kV and the sample was sputter coated with a 50 nm layer of platinum to improve thermal conductivity and prevent sample melting during measurement. Focused-ion-beam (FIB) milling of the CsA agglomerates (produced with 0.025% w/v lecithin and 1% w/v lactose) was performed in an FIB/scanning electron microscope dual beam system (Quanta 200 3D, FEI, USA) using a similar procedure described previously, but without the cleaning step (Heng et al., 2007). The CsA powder was mounted onto a 100-mesh transmission electron microscopy grid (GCu100, ProSciTech, Australia) and coated with a 50 nm layer of gold. Vertical cutting of the sample was performed at a stage tilt of 52◦ with an accelerating voltage of 10 kV and a beam current of 16 pA. Milling times was kept under 5 min. The milled agglomerates were later examined using the high-resolution SEM (JSM 6000F, Joel, Japan) at 3 kV, as the milled surface is not coated, and tilted at 30◦ to examine the cut surface. 2.2.5. Particle size determination and powder dispersion A dry powder feeder (Sirocco, Malvern, Worcs, UK) connected to a laser diffractometer (Mastersizer 2000, Malvern, Worcs, UK) allowed a rapid means to screen the dispersion behaviour of the processed powders to help identify the optimal CLIJ experimental conditions. The change in the volume-weighted particle size distribution (PSD) of the
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Fig. 2. Schematic diagram of the dry powder feeder.
CLIJ-spray dried CsA agglomerates as a function of the dispersing air pressure (i.e. a pressure titration) was determined using the refractive indices of CsA (1.578 and 0.100 for the real and imaginary components, respectively) and the dispersing air (1.000). The pressure titration study was performed at various air pressures (between 0.5 and 4 bars) and the resulting PSD was measured until the maximum pressure was reached or the powder was apparently fully dispersed (as shown by reaching a plateau of the particle size in the titration curve). During the measurement, the sample powder (5–10 mg) was shaken from a vibrating sample tray where the sample was then blown by compressed air, introduced at a set pressure, against and around a bend then across the lens for the PSD measurement (Fig. 2). Once identified in the laser-diffraction measurement, the optimal aerosol performance of the powders was then confirmed on a commercial inhaler. 2.2.6. Aerosol performance While the dry powder feeder can indicate the relative product performance among the samples, it is not an inhaler, suitable for patient use. As the aim of this study is to produce CsA for dry powder inhalation, the aerosol dispersion behaviour of the best performing powder was realistically assessed using an Aeroliser 䉸 (Novartis Pharmaceuticals, Australia) coupled through an USP stainless steel throat to a multi-stage liquid impinger (MSLI, Copley, UK), operating at 60 and 100 L/min. Powder (10.0±0.5 mg) was filled into hydroxypropyl methylcellulose capsules (size 3, Capsugel䉸 , USA) and single capsules were used in each experiment. Measurements were performed in duplicate. CsA deposited at different locations was assayed by UV spectrophotometry (U-2000, Hitachi, Japan) at 214 nm. A linear calibration curve of CsA in ethanol was constructed in the concentration range of 5.40 g/mL [concentration (g/mL)=38.896× absorbance + 1.851; R 2 = 0.9875]. Fine particle fraction (FPF) is defined as the mass fraction of drug particles smaller than 5 m in the aerosol cloud (interpolated from the mass of drug collected from stages 3, 4 and filter) relative to the total mass recovered. 2.2.7. Visualisation of agglomerate dissociation Dissociation of the primary particles from CsA agglomerates was visualised under an optical microscope (BX60, Olympus, Japan), connected to a digital microscope camera (AxioCam, Carl Zeiss, Germany) for image recording (AxioVision V4.6.1.0., Carl Zeiss, Germany). CLIJ-spray dried CsA powder (0.025% w/v lecithin and 1% w/v lactose) sandwiched between a glass microscope slide and cover slip was initially imaged. The cover slip was then removed and a drop of deionised water was introduced directly to the sample. The slip was immediately replaced and further images of the sample were taken. 3. Results and discussions 3.1. Powder properties—crystallinity, particle size, and morphology All CsA powders from the CLIJ precipitation process followed by spray drying have a similar X-ray diffraction pattern compared with the initial material (Fig. 3), all appearing to be amorphous. While it is possible that they are thermotropic liquid crystals (Lechuga-Ballesteros, Abdul-Fattah, Stevenson, & Bennett, 2003), it is unlikely since optical birefringence was absent using polarising microscopy. The contribution of the two additives to crystallinity is minimal considering the amounts used. The primary particles of the CLIJ precipitated CsA were spherical and the shape was maintained in the agglomerates after spray drying (Figs. 4A and B). Depending on the concentration of the additives used, the CsA primary particle size in the agglomerates ranges between 180 and 700 nm, as observed by SEM images (Figs. 4A and B), whereas the agglomerates are of approximately 1 m. As shown in the SEM images
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Fig. 3. X-ray diffraction patterns of CsA powders (
initial material, · · · CLIJ mixing with 1% w/v lactose and 0.025% w/v lecithin).
Fig. 4. SEM images of CsA powder after (A) spray drying of the suspension produced with 0.025% w/v lecithin with 1% w/v lactose and (B) the same powder sectioned perpendicular to the supporting plane by FIB with the plane tilted to show more of the cut face.
after sectioning by the FIB milling (Figs. 4C and D), these agglomerates are not hollow, hence they are not similar to other spray dried nanoparticle agglomerates such as Trojan particles (Tsapis et al., 2002). The sectioned faces reveal that they appear to be typical agglomerates rather than hollow particles with shell composed of agglomerates. 3.2. Dry powder dispersion of CsA product The size–pressure titration profiles (Fig. 5) for all of the nine samples are grouped by the lactose content (low, medium, and high). All samples show a decrease in the apparent agglomerate size of the bulk powder with increasing dispersing air pressure, and at the lower pressures this is the smallest for the sample containing the highest level of lactose and lecithin. At sufficiently high pressures the samples could be dispersed to aerosols of a similar volume median diameter of around 1 m, regardless of the additive concentrations. Each profile can be fitted to a simple power law, expressed as volume median diameter (VMD) = a + b × disperser pressurec .
(1)
Expression (1) is an empirical equation linking the VMD of the powder agglomerates to various curve-fitting parameters, where parameter “a” is related to the minimal agglomerate size that is achievable in the dry powder disperser, “b” to the extent of agglomerate size change during dispersion, and “c” to how readily the agglomerates break up on increasing disperser pressure. A small VMD would require a small value of a, b, and/or c. The effect of the additives on these
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Fig. 5. Pressure titration profile of the spray dried CLIJ processed powders at different lecithin concentrations ( – – – 0.025% w/v) and low (A, 0.01% w/v), medium (B, 0.1% w/v), and high (C, 1% w/v) levels of lactose.
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0.00025% w/v, · · · 0.0025% w/v,
parameters is shown as contour plots for which the additive concentrations for optimal aerosolisation (i.e. resulting in the smallest VMD) were identified (Fig. 6). As reflected by the parameter a values (Fig. 6A), the agglomerate size decreased only slightly to 0.7 m from the original agglomerate size of around 1 m, indicating that the dry powder feeder did not fully disperse the agglomerates into the primary particles of 180–700 nm in size (Fig. 4) at the highest disperser pressure available. The parameters b and c describe the extent, and the rate, of change in size of the agglomerates, respectively. Hence, they are related to the force required to break the agglomerates which, in turn, determines the dispersion performance. Below 0.1% w/v lactose, parameter b ranges between 1.0 and 1.4 m/bar, and it depends predominantly on the concentration of lecithin rather than lactose. Above the critical concentration of 0.1% lactose, the value of parameter b reduces to 0.6 m/bar, and the change is no longer dependent on the lecithin concentration (Fig. 6B). According to Eq. (1), a reduced b value would mean a smaller VMD for the agglomerates. Overall, higher concentrations of lactose reduce the b value, which helps dispersion particularly at lower disperser pressures. The parameter c is influenced by both the lecithin and lactose concentrations (Fig. 6C). It is always negative as the VMD is decreasing with increasing air pressure. High concentrations of both lactose and lecithin favour a value close to zero for c, indicating that the agglomerates are easier to disperse. The results suggest that the presence of the additives at a high concentration may coat the particles sufficiently to reduce the inter-particulate forces required to separate the agglomerates. A value of zero for c shows that the VMD is independent of disperser pressure. While both lactose and lecithin contribute to the stability of the CsA particles during spray drying, they operate by different mechanisms. Lecithin, as an amphiphilic molecule accumulates on the CsA particle surface during the initial formation step in the impinging jet mixing (Johnson & Prud’homme, 2003c). This surface layer control particle aggregation of the primary particles in the initial solution stage. During spray drying the primary particles are concentrated as water evaporates. The polar component moieties of the lecithin molecule provide a steric and electrostatic barrier to prevent contact between particles and fusion. A fused CsA aggregate would both be too large in size, would not readily fragment down to the desired aerodynamic size during dispersion, and would not readily dissociate back to the primary
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Fig. 6. Contour plots of parameters (A) “a”, (B) “b”, and (C) “c” against lecithin and lactose concentrations.
particle size when re-hydrated. Hence, the lecithin mode of action is as an interfacially active surfactant. In contrast, lactose is completely hydrophilic and has no tendency to interact with the CsA particle surface so it has little effect during particle formation in the wet state. However, during drying, the concentration of the lactose causes the aqueous phase to first increase in viscosity and finally form a solid amorphous phase with a sticky nature (Chiou & Langrish, 2007). The lactose physically immobilizes the CsA primary particles either embedded in this amorphous phase or stuck together. Presumably, the aerosol aggregate size is controlled by bridges and interfaces between hydrophilic lactose solid regions and hydrophobic CsA surfaces. The aerosol fragmentation of these aggregates would depend, in rather complicated ways on the relative volume fractions of the components and their interfacial adhesion. During re-hydration the soluble lactose can dissolve and the CsA particles return to their original size prior to spray drying. Both lecithin and lactose play a role in the spray drying of the CsA—the former chemically based and the latter steric in nature. The size–pressure titration profiles show that powders with a medium level of lecithin (0.0025% w/v) are less dispersible compared with the low or high levels (Fig. 5). This could be due to the difference in the extent of surface coverage of CsA particles by lecithin (Fig. 7). At low surface coverage, deagglomeration is dominated by the surface forces between the hydrophobic CsA particles. As lactose concentration is increased, so is the surface coverage and a monolayer may actually form at the medium additive level. Since the lecithin molecules will adsorb on the CsA surface via hydrophobic interactions, the polar groups of lecithin will be sticking out making the CsA surface more polar, which may contribute to the decreased dispersibility of the CsA particles. At a high lecithin level when the surface is covered with excess additives (i.e. multilayer), deagglomeration depends mainly on interactions between the additives. The excess lecithin molecules will initially interact via their hydrophilic groups with those in the monolayer, resulting in the polar groups exposing to the aqueous environment. However, the situation can be complex, as the structure will collapse when water is removed in drying and hence the interactions can change. The resulting CsA surface is
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Fig. 7. Surface coverage of lecithin on CsA particles.
likely to be hydrophobic, as suggested by the similarity between the titration profiles of the low and high levels of lecithin. In summary, whereas high lactose level alone reduces the values of parameter b and high lecithin level reduces the parameter a, high levels of both lecithin and lactose reduce the magnitude of parameter c. These results confirm that CLIJ precipitation of CsA in the presence of 0.025% w/v lecithin and 1% w/v lactose followed by spray drying could produce a powder with good aerosol dispersion performance. 3.3. Aerosol performance While the dry powder feeder is capable of comparing the intrinsic aerosolisation behaviour of the various powders, it is not suitable as an inhaler for patient use. The CsA powder determined by the dry powder disperser as the optimum was thus subsequently dispersed using a commercial dry powder inhaler, the Aeroliser 䉸 . The FPF of powder less than 5 m was found to be 54.2 ± 2.2% and 56.8 ± 0.02% at 60 and 100 L/min, respectively, with the majority of the powder deposited on stage 3 and below (Fig. 8). The FPF relative to the emitted dose are 66.2 ± 2.1% and 78.0 ± 0.1% at 60 and 100 L/min, respectively. Minimal throat deposition (4–5%) suggests the agglomerates that exit the inhalation device are small, reflecting the results obtained from the dry powder feeder (Fig. 5C). Based on a whole lung deposition of 60–70% relative to the FPF of powder less than 5 m (Clark & Borgstrom, 2002), the 10 mg of powder loaded in the capsule for dispersion would translate to between 3.3 and 3.8 mg of CsA deposited in the lung. This is about the minimum amount required (5 mg) to improve the pulmonary function of lung transplant patients with chronic rejection (Corcoran et al., 2004). This amount could be achieved with two capsules or a higher loading in a single capsule, compared with a metered dose inhaler formulation requiring five actuations to achieve approximately half the minimum amount required (Myrdal et al., 2004). 3.4. Dissociation of CsA agglomerates When the CLIJ-spray dried CsA powder (containing 0.025% w/v lecithin and 1% w/v lactose) came in contact with water, the agglomerates were observed to dissociate with the resulting smaller fragments or primary particles in size below 1 m (Fig. 9). The dissociation can readily be attributed to dissolution of the water soluble additives in the agglomerates. It must be noted that the purpose of the experiment was not to simulate what would happen in the lungs (which necessitates a separate in vivo study). While deionised water did not mimic the lung lining fluids, the result showed that the primary particles of CsA did not fuse together and become undissociable during the precipitation–spray drying process. Based on the in vitro results, we speculate that the agglomerates will dissociate into the nanoparticles followed by dissolution in the lungs. Despite the presence of the hydrophobic portion of the phospholipids on the
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Fig. 8. Percentage of mass deposited on each stage of multi-stage liquid impinger. The cutoff diameters of stages 1, 2, 3, and 4 calibrated at 60 L/min √ (white) are 13.0, 6.8, 3.1, and 1.7 m; at 100 L/min (grey) the cutoff diameters were calculated using D50 calc = D50 calc Qcalib /Qcalib (where D50 and Q are the cutoff diameter and flow rate, respectively, for the calibrated (calib) and calculated (calc) values) to be 10.1, 5.3, 2.4, and 1.3 m.
Fig. 9. Dissociation of CsA agglomerates, prior to (A) and after the addition of water (B) under optical microscopy.
particle surface, lung surfactants in the airways may help facilitate the dissociation process. The study will continue in the future to include such in vivo work. 4. Conclusion In conclusion, CLIJ precipitation coupled with spray drying is suitable for producing inhalable peptides. Strong aerosol performance of the CsA powder is achieved without the use of large carrier particles but with minimal concentrations of additives in the precipitation process. The required clinical dosage to improve the pulmonary function of lung transplant patients could potentially be achieved with two doses. Pressure titration was found to be a quick method to determine the suitability of dry powders for inhalation drug delivery. Acknowledgements This work was supported by a grant from the Australian Research Council (DP 0451940). DH is a recipient of the Australian Postgraduate Award (Industry). One of the authors (J.A.R) is located at the NSF. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. RKP acknowledges financial support from the NSF NIRT grant on Nanoparticle Formation and the Bill and Melinda Gates Foundation grant to Harvard University.
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References Benet, N., Muhr, H., Plasari, E., & Rousseaux, J. M. (2002). New technologies for the precipitation of solid particles with controlled properties. Powder Technology, 128, 93–98. Brodka-Pfeiffer, K., Langguth, P., Grass, P., & Hausler, H. (2003). Influence of mechanical activation on the physical stability of salbutamol sulphate. European Journal of Pharmaceutics and Biopharmaceutics, 56, 393–400. Chan, H.-K. (2006). Dry powder aerosol drug delivery—Opportunities for colloid and surface scientists. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 284–285, 50–55. Chiou, D., & Langrish, T. A. G. (2007). Crystallization of amorphous components in spray-dried powders. Drying Technology, 25, 1427–1435. Chiou, H., Chan, H.-K., Prud’homme, R. K., & Raper, J. A. (2008). Evaluation on the use of confined liquid impinging jets for synthesis of nano-drug particles. Drug Development and Industrial Pharmacy, 34, 59–64. Chiou, H., Li, L., Hu, T., Chan, H.-K., Chen, J.-F., & Yun, J. (2007). Production of salbutamol sulfate for inhalation by high-gravity controlled antisolvent precipitation. International Journal of Pharmaceutics, 331, 93–98. Clark, A., & Borgstrom, L. (2002). In vitro testing of pharmaceutical aerosols and predicting lung deposition from in vitro measurements. Lung Biology in Health and Disease, 162, 105–142. Corcoran, T. E., Smaldone, G. C., Dauber, J. H., Smith, D. A., Mccurry, K. R., Burckart, G. J. et al. (2004). Preservation of post-transplant lung function with aerosol cyclosporin. European Respiratory Journal, 23, 378–383. Galeazzia, M., Bellisaia, F., Manganellia, S., Morozzia, G., & Sebastianib, G. D. (2006). Cyclosporine A for the treatment of autoimmune disorders in HCV infected patients. Autoimmunity Reviews, 5, 493–498. Garimella, S. V., & Rice, R. A. (1995). Confined and submerged liquid jet impingement heat transfer. Journal of Heat Transfer, 117, 871–877. Heng, D., Tang, P., Cairney, J. M., Chan, H.-K., Cutler, D. J., Salama, R. et al. (2007). Focused-ion-beam milling: A novel approach to probing the interior of particles used for inhalation aerosols. Pharmaceutical Research, 24, 1608–1617. Iacono, A. T., Johnson, B. A., Grgurich, W. F., Youssef, J. G., Corcoran, T. E., Seiler, D. A. et al. (2006). A randomized trial of inhaled cyclosporine in lung-transplant recipients. The New England Journal of Medicine, 354, 141–150. Johnson, B. K., & Prud’homme, R. K. (2003a). Chemical processing and micromixing in confined impinging jets. AIChE Journal, 49, 2264–2282. Johnson, B. K., & Prud’homme, R. K. (2003b). Engineering the direct precipitation of stabilized organic and block copolymer nanoparticles as unique composites. Polymeric Materials Science and Engineering, 89, 744–745. Johnson, B. K., & Prud’homme, R. K. (2003c). Flash nanoprecipitation of organic actives and block copolymers using a confined impinging jets mixer. Australian Journal of Chemistry, 56, 1021–1024. Johnson, B. K., & Prud’homme, R. K. (2003d). Mechanism for rapid self-assembly of block copolymer nanoparticles. Physical Review Letters 91, 118302/118301–118302/118304. Lechuga-Ballesteros, D., Abdul-Fattah, A., Stevenson, C. L., & Bennett, D. B. (2003). Properties and stability of a liquid crystal form of cyclosporine—The first reported naturally occurring peptide that exists as a thermotropic liquid crystal. Journal of Pharmaceutical Sciences, 92, 1821–1831. Lechuga-Ballesteros, D., Bennett, D., Cabot, K., Farinas, K., Gong, D., Hastedt, J. et al. (2000). Aerosol drug development of a spray dried liquid crystalline formulation of cyclosporine. In: R. N. Dalby, P. Byron, S. J. Farr, & J. Peart (Eds.), Respiratory drug delivery VII Tarpon Springs, Florida: Serentec Press. Myrdal, P. B., Karlage, K. L., Stein, S. W., Brown, B. A., & Haynes, A. (2004). Optimized dose delivery of the peptide cyclosporine using hydrofluoroalkane-based metered dose inhalers. Journal of Pharmaceutical Sciences, 93, 1054–1061. Sham, J. O. H., Zhang, Y., Finlay, W. H., Roa, W. H., & Lobenberg, R. (2004). Formulation and characterization of spray-dried powders containing nanoparticles for aerosol delivery to the lung. International Journal of Pharmaceutics, 269, 457–467. Tsapis, N., Bennett, D., Jackson, B., Weitz, D. A., & Edwards, D. A. (2002). Trojan particles: Large porous carriers of nanoparticles for drug delivery. Proceedings of the National Academy of Sciences of the United States of America 99, 12001–12005. Underwood, S. L., Mcmillan, S., Reeves, R., Hunt, J., Brealey, C. J., Webber, S. et al. (2001). Effects of cyclosporin A administered into the airways against antigen-induced airway inflammation and hyperreactivity in the rat. European Journal of Pharmacology, 420, 165–172. (2003). In: H. Van De Waterbeemd, H. Lennernäs, & P. Artursson (Eds.), Drug bioavailability: Estimation of solubility, permeability, absorption and bioavailability Weinheim, Germany: Wiley-VCH. Wang, X., Gillian, J. M., & Kirwan, D. J. (2006). Quasi-emulsion precipitation of pharmaceuticals. 1. Conditions for formation and crystal nucleation and growth behavior. Crystal Growth & Design, 6, 2214–2227. Zijlstra, G. S., Rijkeboer, M., Van Drooge, D. J., Sutter, M., Jiskoot, W., Van De Weert, M. et al. (2007). Characterization of a cyclosporine solid dispersion for inhalation. AAPS Journal, 9, E190–E199.