Evaluation of the Transwell System for Characterization of Dissolution

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Evaluation of the Transwell® system for characterization of dissolution behavior of inhalation drugs: Effects of membrane and surfactant Marc Rohrschneider, Sharvari Bhagwat, Raphael Krampe, Victoria Michler, Jörg Breitkreutz, and Guenther Hochhaus Mol. Pharmaceutics, Just Accepted Manuscript • DOI: 10.1021/acs.molpharmaceut.5b00221 • Publication Date (Web): 19 Jun 2015 Downloaded from http://pubs.acs.org on July 6, 2015

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Molecular Pharmaceutics

Evaluation of the Transwell®system for characterization of dissolution behavior of inhalation drugs: Effects of membrane and surfactant Marc Rohrschneider[1] †, Sharvari Bhagwat[2] †, Raphael Krampe[2], Victoria Michler[2], Jörg Breitkreutz[3], Günther Hochhaus*[2] [1]

Boehringer Ingelheim GmBH & Co KG, Bingerstasse 173, 55216 Ingelheim am Rhein,

Germany. [2]

University of Florida, College of Pharmacy, Gainesville, Florida 32610, USA.

[3]

Heinrich Heine Universität Düsseldorf, Universitätsstrasse 1, 40225 Düsseldorf, Germany.

KEYWORDS inhaled corticosteroids, inhalation, dissolution methods, Transwell®, dissolution medium.

ABSTRACT Background: Assessing the dissolution behavior of orally inhaled drug products (OIDs) has been proposed as an additional in vitro test for the characterization of innovator and generic drug development. A number of suggested

dissolution methods (e.g. commercially available

Transwell® or Franz cell systems) have in common a membrane which provides the separation between the donor compartment, containing non-dissolved drug particles, and an acceptor (sampling) compartment into which dissolved drug will diffuse into. The goal of this study was to identify and overcome potential pitfalls associated with such dissolution systems using the

ACS Paragon Plus Environment

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inhaled corticosteroids (ICS) viz., budesonide, ciclesonide and fluticasone propionate as model compounds. Method: A respirable fraction (generally stage 4 of a humidity, flow and temperature controlled Andersen Cascade Impactor (ACI) or a next generation impactor (NGI) was collected for the tested MDI’s. The dissolution behavior of these fractions was assessed employing the original and an adapted Transwell® system using dissolution media which did or did not contain surfactant (0.5% sodium dodecyl sulfate). The rate with which the ICS transferred from the donor to the acceptor compartment was assessed by HPLC. Results: Only a modified system that incorporated faster equilibrating membranes instead of the original 0.4 μm Transwell® membrane resulted in dissolution and not diffusion being the rate limited step for the transfer of drug from the donor to the acceptor compartment. Experiments evaluating the nature of the dissolution media suggested that the presence of a surfactant (e.g. 0.5 % SDS) is essential to obtain rank order of dissolution rates (e.g. for budesonide, fluticasone propionate and ciclesonide) that is in agreement with absorption rates of these ICS obtained in human PK studies.

Using the optimized procedure, the in vitro dissolution behavior of

budesonide, ciclesonide and fluticasone propionate agreed approximately with descriptors of in vivo absorption. Conclusion:

The optimized procedure, using membranes with increased permeability and

surfactant containing dissolution medium represents a good starting point to further evaluate in vitro/ in vivo correlations.


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1. INTRODUCTION Inhaled corticosteroids (ICS) are the main anti-inflammatory therapy in persistent asthma worldwide [1]. They are also used to treat other inflammatory based respiratory diseases such as chronic obstructive pulmonary disease (COPD) [2]. ICS particles when inhaled orally will deposited onto the lung lining fluid and have to dissolve in the lung fluids, before being locally available. The dissolution of inhaled ICS particles is often the rate-limiting step for drug entering the relevant pharmacodynamics cells or being absorbed into the systemic circulation, because of their high lipophilicity. The dissolution rate, determining the drug’s pulmonary residence time has been shown to be important for the degree of pulmonary targeting [3-5]. In vitro tests assessing the dissolution behavior of OIDP will be of relevance for describing the in vivo situation if relevant in vitro conditions can be identified. The IPAC-RS Dissolution Working Group concluded that dissolution testing is a valuable technique in the development of inhaled dosage forms, but that a standardized method has not been proposed [7]. Different laboratories have proposed several dissolution test methods (Transwell® system, USP paddle or flow through systems), or provided reviews and abstracts on the implications of dissolution testing for inhaled products [8-11]. The aim of this study was to further optimize a fluid capacity limited dissolution system (Transwell® system). Main aims of this study (i) were to test whether the commercial Transwell® system or suitable modifications are suitable to assess the dissolution behavior of three model corticosteroids differing in lipophilicity (budesonide, fluticasone propionate and ciclesonide), (ii) to identify a suitable dissolution medium and (iii) to probe whether under these conditions, dissolution rates of budesonide (BUD), ciclesonide (CIC) and fluticasone propionate (FP) can be related to the pulmonary absorption rates obtained from the literature.


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2. EXPERIMENTAL SECTION Materials. All dissolution experiments were conducted using MDI formulations of ciclesonide (Alvesco®, 60 µg ciclesonide HFA-MDI, Sepracor Inc., Marlborough) the FP containing Flixotide (110 µg FP, GSK HFA-MDI) and Budesonide containing Symbicort® (AstraZeneca 80 mcg of Budesonide). A 6 well 24mm Transwell® system with 0.4 µm pore size polyester membrane inserts (Corning, Inc., Acton, MA) were used for the dissolution studies. 24 mm glass microfiber filters (Whatman GF/C) or Fisherbrand Q8 filter papers to capture the particles onto and transfer to the dissolution set-up. Acetonitrile (HPLC Grade), Ethanol (HPLC Grade), Sodium Dodecyl Sulfate (SDS), Potassium Sulfate and Phosphate Buffered Saline Solution (PBS) were purchased from Fisher Scientific, Pittsburgh, PA. ACI and NGI sample collection.

An 8-stage stainless steel Andersen Cascade Impactor

(Copley Scientific, Nottingham, UK) was used together with a flow control and a measuring unit at 28.3 L/min. Humidity (100% at 37 oC was maintained using an external humidifier device.1 In some experiments, a seven stage Next Generation Impactor was employed along with a flow control and measurement unit and a pump (Copley Scientific, Nottingham, UK). In all impactor runs, three 24 mm diameter filter papers were placed on stage 4 of the ACI or NGI to capture material to be used within the dissolution test. In order to deposit an amount suitable to follow by HPLC, the MDI was actuated up 5 times to achieve an average amount of drug deposited onto the filter of about 10 µg. Dissolution Test. The filter paper was immediately transferred face-up to the donor compartment of setup A or B [Figure 1]. Setup A used the original Transwell® donor compartment and was similar to that described by Arora et al. [8]. For setup B, the polycarbonate membrane was removed from the donor compartment and mild heat was used to form notches in the base in order to support the glass microfiber filter/filter paper that would be placed on it.

1

As these conditions are not crucial for the here proposed work, details of the set-up are not provided.


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For both set-up A and B, the filter paper carrying the drug was placed face up into the donor compartment of the Transwell® system. This donor compartment was placed in the 6 well plate and 1.5 mL of dissolution medium (generally 0.5% SDS in PBS). The experiment was initiated by placing 0.1 mL of the dissolution medium onto the filter paper. In experiments, evaluating the transfer of already dissolved drug, 10 µg of the drug was dissolved in the initiating medium (generally 0.5% SDS in PBS). Samples of 0.5 ml were taken at 0, 10, 20, 30, 45, 60, 90, 120, 180, 240 and 300, 360, 420, 480, 1440 min or for set up A and 0, 10, 20, 30, 45, 60, 90, 120, 180, 240 and 300, 360,480,720 min (or equivalent time points) for set-up B. Removed volumes were replenished with fresh dissolution medium. After the final sample was taken, the filter membranes were removed, washed with methanol to analyze the amount of undissolved drug. Three to nine replicates were performed for a given experiments. Smaller number of replicates (n=3) were selected for preliminary experiments (e.g. evaluation of the effects of the Transwell ® membrane on transfer rates, ability to distinguish transfer rates of solution and drug particles, comparison of dissolution media with and without surfactant) while more qualitative assessments such as the comparison of mean dissolution times of the model compounds were performed in experiments using nine replicates. In some experiments, (experiments for demonstrating the effect of surfactant in the medium and experiments to test the sensitivity to differences in particle size) a slightly adapted dissolution method was used. The changes included (1) replacing the filter paper with a glass microfiber filter, (2) addition of a stirrer in the acceptor compartment, (3) addition of a supporting mesh under the microfiber filter paper, (4) addition of an extra 100 μl of the dissolution medium, making the total volume to 1.6 ml. The samples were placed in an incubator maintained at 37 0C and stirred continuously. A saturated solution of potassium sulfate was placed in the oven to maintain humidity conditions. This adaptation was cross-validated with the original set-up B by achieving similar mean dissolution time for fluticasone propionate.


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HPLC analysis. Rapid, accurate, precise and linear HPLC methods were developed (R2 > 0.999) for analysis of budesonide, fluticasone propionate and “intact” ciclesonide prodrug. Samples were diluted with 50% methanol: 50% water and analyzed using an Inertsil ODS-3® column with a mobile phase of 70% acetonitrile : 30% water for fluticasone propionate and budesonide at a flow rate of 1 ml/min, and 80% acetonitrile:20% water for ciclesonide at 1.2 ml/min. Wavelength was set at 254 nm. Solubility testing. 10 mg of drug was weighed and placed in a flask containing 10 ml of the dissolution medium. The suspension was stirred at 37o C in an incubator for 24 hours. After 24 hours, 1 ml of the suspension was pipetted into a micro-centrifuge tube and centrifuged for about 1 minute to settle the undissolved particles. The clear supernatant solution was diluted with 50% methanol: 50%water and analyzed using HPLC. All experiments were done in triplicate. Data Analysis. Calculations were performed in Microsoft Excel®. The amount of dissolved drug in the samples removed at each time point was taken into account while calculating the percentage of drug dissolved. The mean dissolution time (MDT) was used as metric to quantify the dissolution rate, as it is a model-independent parameter. Results can also be easily compared with non-compartmental pharmacokinetic parameters, such as the mean absorption time (MAT). Mean dissolution times were calculated from plots showing the amount of undissolved drug as a function of time. The MDT was defined as the ratio of AUMC/AUC where AUMC represents the area under the first moment curve and AUC the area under the curve of undissolved drug vs time plots. Mean absorption times (MAT) of fluticasone propionate and budesonide were obtained from literature. In case of ciclesonide, necessary data to calculate MAT was extracted from graphical representations of the mean ciclesonide prodrug concentrations vs time plots after i.v. administration and inhalation of ciclesonide from metered dose inhalers. MAT was defined as the difference between the mean residence time after inhalation and after intravenous injection.


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3. RESULTS Preliminary experiments were performed to validate the Transwell® system. First, the original Transwell® setup (Setup A) which uses a 0.4 μm polycarbonate membrane was tested by placing the drug containing filter paper (drug particles collected from stage 4 of the ACI onto filter paper or applied directly as solution, see Methods) onto the Transwell® membrane. These experiments indicated that the transfer rate observed for particles of ciclesonide (i.e., combined rate of dissolution and diffusion of solid drug from donor to acceptor compartment) and that of ciclesonide solution (i.e., rate of diffusion of dissolved drug across membrane) were indistinguishable. Transfer of ciclesonide when provided as solution using setup B (without the 0.4 um polycarbonate membrane) was faster than that observed with setup A (diffusion across the 0.4 μm membrane plus filter paper (Figure 2b). Setup B also resulted in a difference (Figure 2c) between the transfer rates of ciclesonide solution (10 µg) and ciclesonide particles which were captured on stage 4 of the ACI (average amount deposited: 15 µg). This indicated that setup B, but not set-up A is able to differentiate between ciclesonide solutions and ciclesonide particles. Because of previous dissolution studies [4], the above experiments evaluating setup A and B were performed in medium containing surfactant (0.5 %SDS). To evaluate the effects of surfactant, dissolution profiles for fluticasone propionate were assessed in both dissolution media. In the absence of surfactant, less than 10% of FP dissolved over a period of 24 hours (Figure 3), indicating a slow and incomplete dissolution of FP over the investigated time range in the absence of surfactant. Evaluating the dissolution profile for ciclesonide was unsuccessful because of the even lower solubility in non-surfactant containing medium which resulted in concentrations below the limit of quantification of the UV-HPLC method (data not shown). Effects of 0.5% SDS on solubility of the model corticosteroids (budesonide, fluticasone propionate and ciclesonide) (Table 1) indicated that not only the solubility but also the solubility rank order changed for the investigated corticosteroids when switching from PBS to 0.5% SDS containing PBS. Dissolution profiles under these conditions are shown for ciclesonide, budesonide and fluticasone propionate (Figure 4). These profiles mirror differences in the solubility of the model compounds in 0.5% SDS (Table 1). Corresponding mean dissolution


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times are shown in Table 1 and compared with literature values of the mean absorption times. To assess the sensitivity of set-up B to mirror differences in particle size, the dissolution profiles of FP-MDI particles collected on Stages 2 and 4 of the NGI were compared and found to be distinctly different (Figure 5).

4. DISCUSSION The importance of assessing the drug dissolution rate as a precursor to drug absorption was highlighted in the early 90’s with the introduction of the biopharmaceutics classification system (BCS) [26]. As the rate of dissolution, not only depends on the intrinsic properties of the drug molecule (e.g. logP), but also on physicochemical characteristics of the drug formulation (amorphous vs crystalline, differences in particle size distribution and other formulation factors), assessing the dissolution rate from dosage forms provides more information than standard solubility studies. This is the reason why assessment of dissolution rates from dosage forms have been used as tool for decision making in drug development and to obtain waivers for in vivo bioequivalence studies [27]. Many commonly used orally inhaled drug products (OIDPs) are delivered using devices such as MDIs and DPIs that deposit drug particles on the lung surface in solid form and from which the drug needs to dissolve and diffuse into the target cells and subsequently the systemic circulations. Poorly soluble compounds delivered to the lung show a sustained absorption over time, which is believed to be dissolution limited [28]. Because undissolved particles, deposited in the upper part of the lung, can be removed through the mucociliary clearance mechanism [29], differences in the dissolution rate not only affect the pulmonary residence time of orally inhaled drugs but also the amount of drug removed through this clearance mechanism and subsequently the pulmonary available dose. Despite the relevance for the local and systemic drug exposure [14], dissolution tests have not yet been incorporated into the arsenal of in vitro tests suggested by regulatory agencies, nor are fully validated methods available. Academic and industrial interest resulted, however, in a number of reports evaluating different approaches for assessing the dissolution behavior of OIDPs [6]. The published methods differ (a)


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in the sample characteristics (raw API, micronized material, formulated API or fine particle fractions collected e.g. through cascade impaction), (b) the nature of the dissolution system (USP paddle dissolution apparatus [30], flow through cells [9] and diffusion controlled devices such as the Transwell® [8] or Franz cell systems [34] and (c) the selected dissolution medium [35] (with or without surfactants such as Sodium Dodecyl Sulfate (SDS), Polysorbate (Tween) and Dipalmitoylphosphatidylcholine (DPPC)). Transwell® and Franz cell systems mimic the lung conditions more closely, as such systems allow particles to dissolve in a volume limited environment. Hence, we selected the Transwell® system as preliminary work from others already existed [8]. However, additional validation of the method was needed to address a number of potential pitfalls. As a diffusion barrier is separating the donor compartment (in which dissolution occurs) from the acceptor compartment phase (from which sampling of dissolved drug occurs), it is vital to ensure that dissolution and not the diffusion across the membrane is the rate-limiting step. A review of the Transwell® system associated literature indicated that this is not necessarily the case [8]. In addition, the nature of the dissolution media has not yet been sufficiently evaluated. While it is known that alveolar type II cells secrete surfactant, such as phosphatidylcholine and phosphatidylglycerol into the lung lining fluid [31], it is not clear whether the addition of surfactant into the dissolution medium is necessary to establish correlations between the dissolution and pulmonary absorption rates. We performed most of the experiments evaluating differences between set-up A and B with dissolution medium containing 0.5 % SDS, as preliminary work suggested its suitability [4]. The importance of the surfactant was evaluated after the dissolution set-up was selected. Some of the published dissolution methods for inhalation drugs were validated with relatively hydrophilic drugs, such albuterol, hydrocortisone and budesonide [10,11]. Results from these studies cannot necessarily be transferred to the more lipophilic, “insoluble” corticosteroids such as fluticasone propionate and ciclesonide. These “insoluble” drugs represent a challenge in dissolution tests as sink conditions are not easily ensured for such compounds in the dissolution systems described above. We selected three commonly prescribed inhaled corticosteroids (budesonide, fluticasone propionate and ciclesonide) as model corticosteroids as they are routinely used in asthma therapy, but their logP values differ significantly (Table 1). This should ensure that differences in the dissolution rate, determined by a suitable dissolution method, might


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be linked to differences in the pulmonary absorption profiles, if the dissolution is the rate limiting step. A recent publication [8] reported that an unmodified Transwell® system (using a 0.4 µm membrane) was unable to differentiate between flunisolide solution and flunisolide particles with respect to their “dissolution” profiles. This suggested that membrane diffusion, and not dissolution, might be the rate limiting step for such systems. While flunisolide is relatively hydrophilic and therefore will dissolve relatively fast, our results with setup A confirmed that this is true even for more lipophilic OIDPs such as ciclesonide [Figure 1 (a)]. To allow for faster diffusion of the dissolved drug, the 0.4 μm pore size membrane of the Transwell® system was removed and replaced with a more permeable filter paper [Figure 1]. Comparing the diffusion of ciclesonide solution through original setup (setup A) and the new one (setup B), indicated that the diffusion of ciclesonide solution was much faster with the filter paper alone (setup B) [Figure 2 (b)]. More importantly, the modified system was able to distinguish between ciclesonide solution (diffusion alone) and ciclesonide particle (dissolution and diffusion) [Figure 2 (c)]. Based on these results, the modified Transwell® system, depicted in Figure 1, that omitted the original 0.4 μm membrane, was selected for further experiments. Under these modified conditions, the system was able to distinguish between transfer rates of solution and particles, and was able to detect differences in the dissolution rate of fluticasone samples collected on stage 2 and 4 of the NGI (Figure 5). This indicated that the rate limiting step is the dissolution and not the diffusion across the membrane. As mentioned previously, pulmonary lining fluid contains phospholipids and phosphoproteins as surface active components [28,31]. As surfactants increase the wetting of deposited drugs and improve the solubility, it was to be expected that the use of surfactants, such as DPPC and SDS will increase the dissolution rate of OIDPs [33] and surfactant use has been suggested as a means of testing poorly water-soluble compounds [22]. We selected 0.5 % SDS containing dissolution medium, as previous work suggested 0.5% SDS’s ability to differentiate between immediate and slow release OIDPs [24,22]. In addition, SDS is readily available, stable in water and not cost prohibitive for use in standard assays as most biological surfactants such as DPPC or lung extracts are. Future studies should however compare


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in more detail synthetic (SDS, Tween 20) with biological surfactants (DPPC, and lung surfactant extracts). When 0.5% SDS was added as a surfactant to the dissolution medium, the solubility of all three corticosteroids improved considerably. Not surprisingly and in agreement with other investigators [24], dissolution rates of the investigated OIDPs (e.g. fluticasone propionate) increased in the presence of 0.5% SDS. Only under these conditions, but not in the absence of surfactant, ciclesonide dissolution curves could be measured, because the low ciclesonide concentrations observed in the absence of surfactant could not be measured by HPLC with UV detection. Most, surprisingly, not only did the solubility increase, but also the rank order of solubility changed with the solubility of ciclesonide now being larger than that of fluticasone propionate [Table 1]. The dissolution rates of the three model compounds were monitored in 0.5 % SDS using slightly different amounts deposited onto the filter paper (Fig.3). It has been reported by others [11] that the dissolution rate of inhaled corticosteroids in some dissolution systems depends on the initial amount of drug provided. While a more detailed characterization of this behavior will be reported in a subsequent publication, we selected initial amounts of the model compounds that considered differences in the compounds solubilities, using higher initial amounts for drugs showing higher solubilities in the dissolution medium, thereby reducing the risk that potential differences in sink conditions would affect the results. Under these conditions (0.5% SDS, similar particle size distribution), the dissolution rate of ciclesonide approached that of the less lipophilic budesonide (Figure 3), quite in agreement with the solubility measurements in 0.5 % SDS, again arguing against a significant effect of the initial amounts on the results. Besides differences in the MDTs due to differences in the physicochemical properties of the drug itself (e.g. log P), it was also of interest to evaluate whether the dissolution method is sensitive to detect differences in formulation dependent parameters. Figure 5 indicated that set-up B is able to detect differences in the dissolution rate between particles collected on stage 2 and 4 of the ACI, potentially assessing differences in the aerodynamic particle size distribution from particles collected as ex-throat material without the necessity of collecting individual stages. Our laboratory used routinely SDS in dissolution tests to increase solubility [4] and achieve sink condition. Not surprisingly, solubility of the three model corticosteroids increased in the


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presence of surfactant (Figure 4). The extent in solubility increase, however, differed among the model corticosteroids ranging from 10 for budesonide to 3000 fold for ciclesonide (Table 1). As a result, not only an increase in solubility, but also a change in rank order of solubility and dissolution rates occurred for the three model corticosteroids when 0.5 % SDS was used (Table 1). This change in rank order prompted the question what dissolution medium (medium lacking or containing surfactant) is more relevant for describing the in vivo situation. Table 1 indicated that the solubility rank orders obtained in 0.5 % SDS and resulting MDTs determined in setup B were much closer to mean absorption times described in the literature. Considering the variability observed in literature values of the MAT for budesonide (Table 1) and the uncertainty associated with the estimation of the MAT for ciclesonide (see footnote 2), the comparison between in vitro and in vivo parameters (Table 1) seems to suggest that MDT and MATs for budesonide and ciclesonide are similar while the much slower dissolution process (MDT in Table 1) for fluticasone propionates is reflected in its much slower pulmonary absorption. This might suggest that setup B generates in vitro metrics that might be predictive for the overall absorption behavior for compounds whose absorption is controlled by the dissolution process. In summary, the dissolution system, whose preliminary validation is presented in this publication, seems to be a promising starting point to further assess potential in vitro in vivo correlation for OIDs.


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Figure 1. Dissolution and diffusion initiation and sampling set-up A and B.


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A

B

C


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Figure 2: (a) Transfer rate of ciclesonide with set-up A and 0.5 % SDS as dissolution medium (lines between data points for visualization only). The rate of drug transfer into the acceptor compartment was determined for already dissolved drug (10 µg, —▲—,n = 3, only diffusion occuring) and for drug particles (5 µg, —♦—, n = 3, dissolution and diffusion occurring; and 10 µg, —●—, n = 3, dissolution and diffusion occurring) (b) Transfer rate of ciclesonide solution, containing total 10 µg dissolved drug, into receptor using set-up A (—♦—, n = 3) and set-up B (—●—, n = 3). (c) Transfer rate of ciclesonide solution, containing 10 µg of dissolved drug (— ●—, n = 9) and. transfer rate of 15 µg of ciclesonide particles collected from stage 4 of the ACI (—♦—, n = 9) using setup B.


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100 80

% Transferred

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60 40 20 0 0

500

1000

1500

Time (min) Figure 3 Dissolution of 15 µg of fluticasone propionate in the presence (—■—, n = 3) and absence (—▲—, n = 3) of 0.5% SDS.


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100

80

% Transferred

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60

40

20

0 0

100

200

300

Time (min) Figure 4. Dissolution profiles of budesonide (20 µg, —▲—, n = 9) fluticasone propionate (10 µg, —●—, n = 9) and ciclesonide (15 µg, —■—, n = 9) using set-up B


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100 80

% Transferred

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60 40 20 0 0

200

400

600

800

Time (min) Figure 5. Dissolution profiles of fluticasone propionate MDI particles collected on stage 2 (— ●—, n = 3) and stage 4 (—▲—, n = 3) of the NGI (Average initial amounts – 10 µg). MDT was not calculated as for stage 2 only 40% of the drug dissolved during the monitored time.


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TABLES

Solubility in PBS ICS

Log P [35]

(µg/ml) at 37OC

Ciclesonide Fluticasone Propionate

Budesonide

4.08 -5.32 3.69-3.72 2.42-2.73

Solubility in 0.5% SDS/PBS (µg/ml) at 37OC

0.015*

setup B

MAT (h)

(h)

300

1.2 ± 0.2

≈ 0.4 [24]

20 ± 3

5 ± 1.2

5-7 [25]

470

0.6 ± 0.1

0.09 [36] 0.14 [39]

MDT in

38.5* 23 [9], 42 [38]

1 (0.3 – 1.8) [13]

Table 1. Solubility in PBS, 0.5 %SDS in PBS, Mean Absorption Time (MAT) and Mean Dissolution Time (MDT) of the model corticosteroids2. *Measured experimentally3.

2

MAT for ciclesonide represents a rough estimate as ciclesonide concentrations for calculations were not available in numerical form, but had to be extracted from semi logarithmic plots after inhalation and i.v. injection of ciclesonide, as shown in [24]. In addition t1/2 of ciclesonide is very short. Considering the MAT range (0.3-1.8 h) reported for budesonide, the uncertainty in the MAT of ciclesonide (about 0.4 h), further studies need to verify whether there is a correlation between solubility/dissolution rate and MAT of these two corticosteroids. What is important is that similar solubility and MDT values result in similar MATs for budesonide and ciclesonide. 3

Refer to Experimental Section for detailed procedure.


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AUTHOR INFORMATION Corresponding Author *Dr Guenther Hochhaus College of Pharmacy, University of Florida PO Box 100494, Gainesville, Florida 32610. Tel no. (352)-273-7861 [email protected]

Author Contributions †co-first authors that contributed equally to this manuscript. The manuscript was written through

contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources Boehringer Ingelheim GmBH & Co.


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Table of Contents Graphic


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Evaluation of the Transwell System for Characterization of Dissolution

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