Numerical simulation of emitted particle characteristics and airway deposition distribution of Symbicort® Turbuhaler® dry powder fixed combination aerosol drug

European Journal of Pharmaceutical Sciences 93 (2016) 371–379

Contents lists available at ScienceDirect

European Journal of Pharmaceutical Sciences journal homepage: www.elsevier.com/locate/ejps

Numerical simulation of emitted particle characteristics and airway deposition distribution of Symbicort® Turbuhaler® dry powder fixed combination aerosol drug Árpád Farkas a,⁎, Ágnes Jókay a, Imre Balásházy a, Péter Füri a, Veronika Müller b, Gábor Tomisa b,c, Alpár Horváth b,c a b c

Centre for Energy Research, Hungarian Academy of Sciences, Konkoly-Thege Miklós út 29-33, 1121 Budapest, Hungary Department of Pulmonology, Semmelweis University, Diós árok 1/C, 1125 Budapest, Hungary Chiesi Hungary Kft., Dunavirág u. 2, 1138 Budapest, Hungary

a r t i c l e

i n f o

Article history: Received 5 July 2016 Received in revised form 18 August 2016 Accepted 19 August 2016 Available online 21 August 2016 Keywords: Inhaled corticosteroid Long-acting β2-agonist Emitted dose Particle size distribution Aerosol drug deposition Computer aided drug delivery optimization

a b s t r a c t One of the most widespread dry powder fixed combinations used in asthma and chronic obstructive pulmonary disease (COPD) management is Symbicort® Turbuhaler®. The aim of this study was to simulate the deposition distribution of both components of this drug within the airways based on realistic airflow measurements. Breathing parameters of 25 healthy adults (11 females and 14 males) were acquired while inhaling through Turbuhaler®. Individual specific emitted doses and particle size distributions of Symbicort® Turbuhaler® were determined. A self-developed particle deposition model was adapted and validated to simulate the deposition of budesonide (inhaled corticosteroid; ICS) and formoterol (long acting β2 agonist; LABA) in the upper airways and lungs of the healthy volunteers. Based on current simulations the emitted doses varied between 50.4% and 92.5% of the metered dose for the ICS, and between 38% and 96.1% in case of LABA component depending on the individual inhalation flow rate. This variability induced a notable inter-individual spread of the deposited lung doses (mean: 33.6%, range: 20.4%–48.8% for budesonide and mean: 29.8%, range: 16.4%–42.9% for formoterol). Significant inter-gender differences were also observed. Average lung dose of budesonide was 29.2% of the metered dose for females and 37% for males, while formoterol deposited with 26.4% efficiency for females and 32.5% for males. Present results also highlighted the importance of breath-holding after inhalation of the drug. About a half of the total lung deposition occurred during breath-hold at 9.6 s average breath-hold time. Calculated depositions confirmed appropriate lung deposition of Symbicort® Turbuhaler® for both genders, however more effort for optimal inhalation technique is advised for persons with low vital capacity. This study demonstrated the possibility of personalized prediction of airway deposition of aerosol drugs by numerical simulations. The methodology developed in this study will be applicable also to other marketed drugs in the future. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Turbuhaler® (also known as Turbohaler® in some countries) was introduced as one of the first multi dose DPIs (dry powder inhaler) in the early nineties. It is currently used with a number of different active substances, named Pulmicort®/Spirocort® (budesonide), Oxis® (formoterol), Bricanyl®/Aerodura® (terbutaline sulphate) and Symbicort® (budesonide/formoterol). The number of studies investigating the characteristics of Turbuhaler® exceeds research on any other dry powder inhaler. For instance, a literature search reveals that the measurement of its internal flow resistance was the subject of at least 25 studies. The mean value of the resistance from these publications is ⁎ Corresponding author. E-mail address: [email protected] (Á. Farkas).

http://dx.doi.org/10.1016/j.ejps.2016.08.036 0928-0987/© 2016 Elsevier B.V. All rights reserved.

about 66 Pa0.5 s L− 1, which means that Turbuhaler® is a medium to high resistance inhaler. In vitro characteristics of the device filled with different drugs have also been extensively studied. Emitted dose, fine particle fraction and mass median aerodynamic diameter (MMAD) of Oxis® Turbuhaler® was determined at different airflow rates by Weuthen et al. (2002) and Nadarassan et al. (2010). The same characteristics of Pulmicort® Turbuhaler® were studied by Feddah et al. (2000); Burnell et al. (2001); Kamin et al. (2002); Munzel et al. (2005) and de Boer et al. (2005), while Meakin et al. (1995); Ross and Schultz (1996); Martin et al. (2007) and Abdelrahim (2010) measured emitted doses and fine particle fractions of Bricanyl® Turbuhaler® at different flow rates. The general conclusion was that both number of particles and their size highly depended on the inspiratory flow rate through Turbuhaler®. In vivo scintigraphy studies of lung deposition of budesonide and terbutaline sulphate emitted by Turbuhaler® were

372

Á. Farkas et al. / European Journal of Pharmaceutical Sciences 93 (2016) 371–379

conducted by several investigators on different population target groups near different peak inhalation flow rates with and without breath-hold. A summary of these studies is provided in Table 1. Deposition fractions are provided as the ratios of the dose (mass) deposited in the lungs to the metered dose. Mean deposition fraction is the deposition fraction averaged over the participants of each study. Lung deposition varied between 14.8% and 29.1% of the metered dose for budesonide and 9.1% and 27% of the metered dose for terbutaline. It is worth noting that due to the limited number of flow rates where radiolabelling of drug particles could be validated with impactor techniques, in most of these studies there were target peak flow rates (e.g. 30 L/min, 60 L/min), thus the applied flow rates do not reflect the whole real life spectrum of flow rates characteristic of the studied populations. A few studies also used the charcoal-block method to measure pulmonary deposition from blood samples (e.g. Borgström et al., 1996; Lahelma et al., 2005). Obviously, considerable research effort was spent also to explore the clinical aspects of the use of these drugs, many times in comparison with the effect of the same drug but emitted from a pMDI (pressurized metered dose inhaler) or with the outcomes of the use of concurrent products. Research interest further increased after the release of Symbicort® Turbuhaler® , an ICS + LABA (inhaled corticosteroid + long-acting β2-agonist; budesonide + formoterol) combination drug firstly in the Swedish market (in 2000), then in about 70 other countries. Emitted doses and particle size distributions of ICS and LABA components were evaluated in vitro at flow rates ranging between 30 L/min and 90 L/min by Tarsin et al. (2004); Assi et al. (2006); Tamura et al. (2012); Johal et al. (2013); Corradi et al. (2014); Gjaltema et al. (2014); Hoppentocht et al. (2014); de Boer et al. (2005) and Buttini et al. (2016). Significant variability of in vitro performance (emitted dose and particle size distribution) of Symbicort® Turbuhaler® with flow rate compared to other DPI drugs was observed. Although the evaluation of lung deposition of Symbicort® Turbuhaler® by scintigraphy is missing in the literature, it is expected that the high flow rate dependence of deposition observed in the case of budesonide is valid also for this two-component drug. Since there is a high intersubject scatter of inhalation parameter values even among healthy people but mainly among patients with lung disease, a high inter-individual variability of the lung deposition of Symbicort® Turbuhaler® can be predicted. However, efficient assessment of lung deposition of every single patient based on their lung function data is possible only if the exact relationships between the relevant breathing parameter and deposition values are known. The conduction of systematic scintigraphic studies on large population groups has both technical and ethical barriers. In contrast, numerical modelling is noninvasive, flexible and reproducible. The aim of this study is to acquire realistic breathing data of individuals inhaling through Turbuhaler®, to determine their emitted drug characteristics, such as individual specific emitted doses and particle

size distributions, and to develop, validate and apply a numerical model for the quantification of patient specific deposition distribution of the inhaled medication using Symbicort® Turbuhaler® within the airways. 2. Methods Breathing parameter values of 25 healthy adult volunteers (11 females and 14 males) have been measured by standard spirometry (PDD-301/s, Piston, Budapest, Hungary) and during their inhalation through Turbuhaler®. No active substance has been inhaled by the volunteers. Signed consent was obtained from the enrolled participants. Lung function values of healthy volunteers were recorded according to the American Thoracic Society guidelines (Miller et al., 2005). Three technically acceptable maneuvers were performed and the highest of them was used. All parameter values were in the physiological range for forced vital capacity (FVC), forced expiratory volume in the first second (FEV1) and the FEV1/FVC ratio. Their mean forced expiratory volume in the first second (FEV1) was 94% (±17.9) of the predicted value, mean FVC was 95.2% (± 18.2) also as a percent of the predicted reference value, while their mean measured FEV1/FVC ratio was 84.5% (±9). The volunteers performed a special breathing mode during their inhalation through the device according to a predefined protocol, that is, forceful inhalation after a forced exhalation, followed by a breath-hold (preferably at least 5‐s) and a slow exhalation. Only the inhalation manoeuvre was performed through the device using an interface to attach the Turbuhaler® to the spirometer. Parameters relevant from the perspective of deposition modelling, like inhalation time (tin), breath-hold time (tb-h), exhalation time (tex) and inhaled air volume (IV) were also acquired. The ratio of IV to tin yields the mean inhalation flow rate (Q), which is an important parameter influencing the number and size distributions of the emitted drug particles and also their deposition within the airways. According to the Summary of Product Characteristics (SPC) of Symbicort® Turbuhaler® the nominal emitted dose of budesonide (ICS component) is 80% of the metered dose (e.g. 200 μg metered and 160 μg nominal emitted budesonide), while the corresponding percentage of formoterol fumarate dihydrate (LABA component) is 75% (e.g. 6 μg metered and 4.5 μg nominal emitted formoterol). It is worth noting that label claim is based on the nominal emitted dose in some countries and on the metered dose in others. The alternate labelled dose values can be misleading for the patients who redeem the same medication in different countries but also for the medical practitioners and even for the scientists analysing different dose dependent properties or effects of the drug. In addition, the nominal dose is emitted only under standardized conditions described in Pharmacopoeias, that is, 4 L of air drawn through the inhaler at a pressure drop of 4 kPa (Council of Europe, 2014; United States Pharmacopeia, 2014). As demonstrated

Table 1 Summary of in vivo scintigraphy studies on lung deposition of budesonide and terbutaline sulphate emitted by Turbuhaler®. The significance of the notations is: PIFm – peak inspiratory flow through the device averaged over the participants of the study and its standard deviation or range, where available; tb-h – average breath-hold time with standard deviation, where available; ηm – average lung deposition fraction with range or standard deviation as a percent of metered dose. Publication

Active substance

PIFm (L/min)

tb-h (s)

Population group

ηm (%)

Thorsson et al. (1998) Newman et al. (2000) Hirst et al. (2001) Borgström and Newman (1993) Borgström et al. (1994)

Budesonide Budesonide Budesonide Terbutaline Budesonide Budesonide Terbutaline Budesonide Budesonide Budesonide Terbutaline Terbutaline Budesonide

67 (49–88) 58 ± 6 64 ± 10 57.8 ± 5.6 58 (50–70) 36 (30–40) 58 73.3 ± 13.7 58 (51–78) 29 (20–35) 56.6 ± 1.7 27.9 ± 0.8 65 (45–76)

10 10.1 ± 0.8 10.4 ± 0.8 9.4 ± 0.6 N8 N8 N8 0 10 10 9 ± 0.3 8.6 ± 0.4 n.a.

8 asthmatic patients 13 healthy adults 12 adults with mild to moderate asthma 8 healthy adults 10 healthy adults

26.1 ± 10.5 21.4 (4.7–29.2) 21.8 ± 8.2 21.4 ± 6.1 27.7 ± 9.5 14.8 ± 3.3 27 ± 7.7 15.8 ± 6.6 28.5 (24–33) 17.8 (14–22) 16.8 ± 2.6 9.1 ± 1.5 29.1 (15.6–47.2)

Warren et al. (2002) Pitcairn et al. (2005) Newman et al. (1991) Wildhaber et al. (1998)

15 healthy adult males 14 adults with mild to moderate stable asthma 10 asthmatic patients 23 asthmatic children (6–16 years)

Á. Farkas et al. / European Journal of Pharmaceutical Sciences 93 (2016) 371–379

computer model. The model was initially developed by Koblinger and Hofmann (1990) and it has been under continuous development. Some features of later developments have been described by Balásházy et al. (2009) and recently by Jókay et al. (2016). The model has been successfully applied to simulate airway transport and deposition of different types of aerosols, like urban aerosols (Salma et al., 2015), bioaerosols (Balásházy et al., 2009; Horváth et al., 2011), radioactive aerosols (Farkas and Balásházy, 2015), tobacco smoke particles (Hofmann et al., 2001) and also aerosol drugs (Balásházy et al., 2007; Farkas et al., 2015; Jókay et al., 2016). Detailed description of the model has been provided by Horváth et al. (2011) and Jókay et al. (2016). Here we briefly recall that in this model the particles are tracked from inhalation until they deposit or are exhaled. Upper airway deposition is computed based on empirical formulas of Stahlhofen et al. (1989). The geometry of the conducting airways is built up stochastically based on distribution functions of airway lengths, diameters, branching angles and gravity angles. The structure of the acinar part is reconstructed based on data of Haefeli-Bleuer and Weibel (1988). The simulated airway geometry can be scaled up and down according to the lung volume of the individual. The main deposition mechanisms taken into account are inertial impaction and gravitational settling. The model is able to account also for deposition by thermal diffusion. However, in the size range of drug particles emitted by Turbuhaler® deposition by Brownian motion is negligible. The model is not accounting for possible particle size changes. 3. Model validation The SLDM model has been validated against various deposition data. In this work we validated the version of the model adapted to the special case of aerosol drugs. From the perspective of the present study the most relevant deposition results are the published lung deposition data of budesonide emitted from Turbuhaler® and evaluated by means of scintigraphy. Deposition measurement results of Borgström et al. (1994); Thorsson et al. (1998); Newman et al. (2000); Hirst et al. (2001) and Pitcairn et al. (2005) were selected, due to the reproducibility of breathing patterns and aerosol particle size distributions described in details in these studies. In the above studies the average flow rate (Q) was around 60 L/min (range: 58–67 L/min), breath-hold time was about 10 s (range: 10.0–10.4 s), while inhaled volume varied between 2.6 and 3.4 L. The results of the comparison are presented in Fig. 1.

computed measured

35 30 25

Lung dose (%)

by systematic inhalation flow profile measurements (Azouz et al., 2015), in real life patients will not perform the same conditions. As a consequence, the actual emitted dose will depend on the force and duration of the inhalation of each individual, thus it will be patient-specific. Knowledge of the exact value of the emitted dose characteristics to each person is a prerequisite for the accurate modelling of individual specific airway deposition. The emitted dose of Symbicort® Turbuhaler® has been measured in vitro under different conditions by several investigators. The measurements were performed by different types of impactors, thus the accuracy of the measurement results may also be different. In this work the measured emitted dose values of Tarsin et al. (2004); Borgström et al. (2005); Assi et al. (2006); Tarsin et al. (2006); Bagherisadeghi et al. (2015); de Boer et al. (2015); Haikarainen et al. (2015); Chrystyn et al. (2015) and Buttini et al. (2016) have been used to derive emitted dose versus inhalation flow rate functions for both components of Symbicort® Turbuhaler®. These mathematical functions and the presently measured individual inhalation flow rate values were then used to determine the individual specific emitted doses. In this work individual emitted doses of budesonide and formoterol were expressed as percentages of the metered dose. In case of drugs released by DPIs not only the emitted total mass (dose), but also the size of the emitted particles is patient specific. Usually, the size distribution of the emitted drug is characterized by an MMAD (mass median aerodynamic diameter) value. However, MMAD is only the median value of the size distribution and particles with diameters both smaller and larger than MMAD occur. As a consequence, particle airway deposition distribution patterns computed based solely on MMAD or based on the corresponding size distribution can be different (Farkas et al., 2015). Moreover, while MMAD is regularly determined based on the drug particles deposited in different stages of the impactor, larger particles emitted by the inhaler and filtered out before their entry into the impactor (thus discounted from the determination of MMAD) will also deposit in the airways, predominantly in the extrathoracic region. For the exact modelling of drug deposition the full drug particle size profile is needed. The internal geometry of the device and the inhalation mode will determine a unique particle size distribution. Aerosolized fraction (the mass fraction of particles entering the impactor) and mass fractions deposited in different impactor stages are known in the published literature for a number of inhalation flow rate values. An extended literature search has been performed to gather the publications containing valuable information on the particle size fractions at different flow rates. The mass size fractions used in this work corresponded to 1 μm, 3 μm, 5 μm, 7 μm and 10 μm. In this study the above size fractions of budesonide and formoterol were determined based on the works of Tarsin et al. (2004); Borgström et al. (2005); Assi et al. (2006); Johal et al. (2013); Corradi et al. (2014); Gjaltema et al. (2014); Hoppentocht et al. (2014); Bagherisadeghi et al. (2015); de Boer et al. (2015); Chrystyn et al. (2015) and Buttini et al. (2016). They provided in vitro size fractions at flow rates between 30 L/min and 90 L/min. The cumulative size fractions (the dose represented by all the emitted particles with diameters lower than a given value expressed as a percent of the metered dose) derived from the above publications were plotted against inhalation flow rate and linear fitting was performed for each specific size fraction (b 1 μm, b 3 μm, b 5 μm, b7 μm and b 10 μm). In this way the cumulative size fractions can be computed for any particular inhalation flow rate (not only for those published in the literature). In this work individual specific drug particle size distributions were determined for the 25 participating volunteers based on the fitted linear functions and the measured individual inhalation flow rates (Q). Regional deposition distributions of the ICS and LABA components of Symbicort® Turbuhaler® were calculated for each participating individual based on the measured breathing parameters, simulated individual specific emitted doses and the corresponding computed particle size distributions by the application of the Stochastic Lung Deposition Model (SLDM), which is a whole respiratory system particle deposition

373

20 15 10 5 0

A

B

C

D

E

Fig. 1. Comparison of simulated lung doses of budesonide expressed as a percent of metered dose with lung dose values measured by scintigraphy techniques retrieved in the open literature. A: Newman et al. (2000), B: Thorsson et al. (1998), C: Pitcairn et al. (2005), D: Hirst et al. (2001) and E: Borgström et al. (1994). The measured dose values in the figure are averages on more subjects, while the error bars represent the dose range (minimum to maximum) of the individual measurements (Newman et al., 2000 and Pitcairn et al., 2005) or standard deviation (Borgström et al., 1994; Hirst et al., 2001 and Thorsson et al., 1998).

374

Á. Farkas et al. / European Journal of Pharmaceutical Sciences 93 (2016) 371–379

Table 2 Average measured respiratory parameter values during standard spirometry measurement (without inhalation devices) and spirometry measurement during inhalation through the device. PIF - spirometric peak inspiratory flow; PIFd - peak inspiratory flow through the device; IVC - inspiratory vital capacity; IV - inhaled volume through the device; tin - inhalation time; tb-h - breath-hold time; tex - exhalation time. Measured parameters

Females + males

Females

Males

Mean

Stdv

Mean

Stdv

Mean

Stdv

Spirometry

PIF (L/min) IVC (L)

333.77 4.12

139.05 1.18

260.4 3.12

113.63 0.78

391.41 4.91

132.78 0.75

Symbicort® Turbuhaler®

PIFd (L/min) IV (L) Q (L/min) tin (s) tb-h (s) tex (s)

90.72 3.54 66.73 3.2 9.6 9.3

29.1 1.27 19.19 0.75 3.99 5.29

78.82 2.68 55.0 3.0 9.8 9.0

32.95 1.07 19.03 0.75 4.62 3.55

100.07 4.23 75.34 3.4 9.4 9.6

22.67 0.97 14.54 0.71 3.59 6.46

As the figure demonstrates the computational results are in good agreement with the measurements performed for similar input data values. The differences between the measured and simulated lung doses are regularly lower than the uncertainties of the measurements shown by the error bars. The good match between the calculated and experimentally determined deposition values indicates that our model is suitable for the simulation of aerosol drug deposition within the airways in general, and modelling of Symbicort® Turbuhaler® deposition in particular. 4. Results and discussion 4.1. In vivo airflow measurements The results of the measurements of the relevant breathing parameters of the 25 participating individuals during standard spirometry and when inhaling through Turbuhaler® are summarized in Table 2. Data in the table represent mean values of the measured breathing parameters averaged over all the participating volunteers, and separately over all males and females. Standard deviations of the measured parameter values are also included in the table. The mean value of the measured inspiratory vital capacity (IVC) is 89.2% (±18.5) of the predicted value. The inhaled volume (IV) is reduced when inhaling through Turbuhaler® (85.9% of IVC for females and 86.2% of IVC for males). This can be due to the additional flow resistance of the device. To increase the volume of inhaled air patients (especially women, who have got lower IV) should exhale forcefully before inhaling the medication. Due to the internal resistance of the device, not only the inhaled volume, but also peak inspiratory flow rate values recorded when the individuals inhaled through the device differ from the ones acquired during standard spirometry measurements. The degree of the reduction of PIF values due to device internal resistance compared to the normal

spirometry PIF (by a factor of 3.7) is in line with the measurement results reported by Janssens et al. (2008). 4.2. Individual emitted doses The left panel of Fig. 2 demonstrates the measured flow rates of the volunteers, while inhaling through Turbuhaler®. Flow rate values range between 29.1 L/min and 101.8 L/min with a mean value of 66.3 L/min. The mean flow rate of women is 55 L/min (range: 29.1 L/min - 82.1 L/min), while the average flow rate characteristic of men is 75.3 L/min (range: 53.8 L/min-101.8 L/min). The dose leaving the inhaler depends on the inhalation flow rate, thus it is patient-specific. In this work the emitted doses of ICS and LABA components were determined separately for each volunteer in a way described in the Methods section. Linear functions were fitted to the measured emitted dose values available in the literature, then individual emitted doses were determined by substituting the individual-specific inhalation flow rates in these functions. Right panel of Fig. 2 shows the emitted dose functions for budesonide and formoterol. According to the figure, the individual specific emitted dose of budesonide expressed as a percent of metered dose varies with flow rate (Q expressed in L/min) as 0.58 × Q + 33.5. The fitted linear function corresponding to formoterol is 0.8 × Q + 14.73. The curves obviously do not yield the emitted doses for any theoretically possible flow rate. Such a curve should evidently start from the origin and would saturate after a certain value of the inhalation flow rate. However, these equations reliably describe the variance of the emitted dose in the 15 L/min–105 L/min flow rate interval (budesonide: r = 0.85, r2 = 0.72, p b 0.0001; formoterol: r = 0.78, r2 = 0.61, p b 0.0001). The distributions of the simulated individual emitted doses calculated by the help of the above linear functions are shown in Fig. 3. Each filled square represents the emitted budesonide dose specific to a Emitted dose

6

ol ter mo r fo e nid eso bud

100 90

5

budesonide: 0.58×Q+33.5 formoterol: 0.8*Q+14.73

Dose (%)

Frequency (-)

80

4

3

70 60 50

2

40

1 30

0 20

40

60

80

Inhalation flow rate (L/min)

100

20

30

40

50

60

70

80

90

100

110

Inhalation flow rate (L/min)

Fig. 2. Distribution of the measured inhalation flow rates (Q) of the 25 individuals when inhaling through Turbuhaler® (left panel) and linear fits to the measured budesonide and formoterol emitted dose values available in the open literature (right panel). Q – inhalation flow rate.

Á. Farkas et al. / European Journal of Pharmaceutical Sciences 93 (2016) 371–379 100

80

<5 µm size fraction

budesonide formoterol mean total mean female mean male

nominal 70

60

50

60

Cumulative dose (%)

Emitted dose (%)

90

budesonide: 0.63×Q-1.1 formoterol: 0.55×Q+0.29

id e

m for

o te

ro l

20

0 20

The computation of individual specific size distributions was preceded by the establishment of cumulative particle size fraction – inhalation flow rate relationships, as described in the Methods section. All cumulative particle size fractions (smaller than 1 μm, 3 μm, 5 μm, 7 μm and 10 μm) expressed as percentages of the metered dose can be written as a × Q + b, where a and b are fitting parameters and Q is the inhalation flow rate in L/min. Fig. 4 illustrates the measured fine particle fractions (the dose represented by particles with aerodynamic diameters smaller than 5 μm expressed as a percent of metered dose) of budesonide and formoterol at different inhalation flow rates and the corresponding fitted functions. Measured data of Tarsin et al. (2004); Borgström et al. (2005); Assi et al. (2006); Tarsin et al. (2006); Tamura et al. (2012); Johal et al. (2013); Corradi et al. (2014); Hoppentocht et al. (2014); Bagherisadeghi et al. (2015); Gjaltema et al. (2014); de Boer et al. (2015); Chrystyn et al. (2015) and Buttini et al. (2016) are plotted. The characteristics of the fits in Fig. 4 are r = 0.88417, r2 = 0.78176, p b 0.0001 for budesonide and r = 0.78244, r2 = 0.61221, p b 0.0001 for formoterol. It is worth noting that the steepness of the fitted lines may be highly influenced by the values at the lower and higher ends, however, only a limited number of measurement results could be retrieved in the literature for flow rates lower than 20 L/min and higher than 75 L/min.

on

30

30

4.3. Emitted particle size distributions

es

40

10

given person, while each empty circle denotes the emitted formoterol dose of an individual as a percent of the metered dose. Mean values of the emitted doses averaged over all the individuals are marked for both drug components (72% for budesonide and 67.8% for formoterol). Gender-specific mean emitted doses are also provided (budesonide mean emitted dose: 65.4% for females and 77.2% for males; formoterol mean emitted dose: 58.7% for females and 74.5% for males). The figure demonstrates the high individual variability of the emitted doses for both drug components (ICS: from 50.4% to 92.5%; LABA: from 38% to 96.1%, expressed as percentages of the metered dose). There are also significant differences between the mean emitted doses characteristic of women and men. For the same person the emitted ICS doses are usually higher than the emitted LABA doses, except four individuals with very high flow rates (over 85 L/min). The large variability of the individual emitted doses is due to the broad range of individual flow rates (see Fig. 2, left panel) and the high sensitivity of the emitted dose to the variance of flow rate. Differences between the emitted doses of females and males can be explained by the differences between the inhalation flow rate values of the two sexes.

d bu

50

40

Fig. 3. Distribution of the simulated individual specific emitted doses of budesonide and formoterol based on the flow profiles measured on 25 healthy adult volunteers. Horizontal lines mark the average values of budesonide and formoterol emitted doses, left arrows the average emitted doses for females and right arrows the average emitted doses for males. Horizontal dashed lines show the nominal emitted doses of budesonide (80% of the metered dose) and formoterol (75% of the metered dose) specified in the SPC.

375

30

40

50

60

70

80

90

100

Inhalation flow rate (L/min) Fig. 4. Linear fits to the measured fine particle fractions of budesonide and formoterol at different inhalation flow rates retrieved in the open literature. Q – inhalation flow rate.

Similar functions were determined for the b 1 μm, b3 μm, b7 μm and b10 μm cumulative size fractions. The corresponding computed values of a and b are presented in Table 3 for both components of Symbicort® Turbuhaler®. The linear relationships with the fitting values in Table 3 do not apply down to zero nor for very high values of the flow rate. According to our tests the derived relationships can be reliably used between 20 L/min and 110 L/min. Fig. 5 depicts sample size distributions of the emitted budesonide and formoterol in case of minimum (29.1 L/min) and maximum (101.8 L/min) measured flow rates and for the mean flow rate (66.3 L/ min) of the 25 individuals based on the above formula and fitting parameter values. To make the interpretation of the distributions easier, the computed cumulative size fractions were transformed into simple (differential) size fractions (size intervals: b 1 μm, between 1 μm and 3 μm, between 3 μm and 5 μm, between 5 μm and 7 μm, between 7 μm and 10 μm and N10 μm). The dose (mass) represented by each size fraction is expressed as a percent of the metered dose, thus the sum of the plotted dose percentages is naturally b100%. As the figure demonstrates the shapes of the distributions corresponding to the two drug components are comparable. While the total emitted dose increases (see also Fig. 2, right panel), the size of the emitted particles (and the corresponding MMADs) decreases with the increase of inhalation flow rate. The number of particles with aerodynamic diameters lower than 3 μm increases sharply, while the number of particles larger than 3 μm decreases. This is reasonable because higher flow rate represents higher force to disintegrate the spherical pellet of the agglomerated particles. In the cases depicted in Fig. 5 MMADs are 3.01 (2.01) μm, 2.35 (1.79) μm and 2.13 (1.74) μm for budesonide at 29.1 L/min, 66.6 L/min and 101.8 L/min inhalation flow rates, respectively. The same values for formoterol are 3.41 (2.14) μm, 2.23 (1.75) μm and 1.88 (1.71) μm, where GSDs (geometric standard deviations) of the size distributions are also provided within parentheses after the MMADs. Similar size distributions were computed for both drug components in case of all the 25 individuals.

Table 3 Computed values of a and b fitting parameters corresponding to budesonide and formoterol for all the considered cumulative particle size fractions. Size fractions

b1 μm b3 μm b5 μm b7 μm b10 μm

Budesonide

Formoterol

a

b

a

b

0.1 0.6 0.63 0.76 0.79

−0.93 −8.47 −1.1 −1.32 −1.39

0.08 0.59 0.55 0.67 0.72

−0.41 −10.43 0.29 0.35 0.38

376

Á. Farkas et al. / European Journal of Pharmaceutical Sciences 93 (2016) 371–379

45

29.1 L/min 66.6 L/min 101.8 L/min

budesonide

40 35

Dose (%)

30 25 20 15 10 5 0

<1

45

1-3 5-7 3-5 Particle diameter (µm)

7 - 10

29.1 L/min 66.6 L/min 101.8 L/min

formoterol

40 35

Dose (%)

30 25 20 15 10 5 0

<1

1-3 3-5 5-7 Particle diameter (µm)

7 - 10

Fig. 5. Simulated size distributions of budesonide (upper panel) and formoterol emitted by Turbuhaler® in case of minimum (29.1 L/min) and maximum (101.8 L/min) measured flow rates and for the mean flow rate (66.3 L/min) of the 25 individuals. The dose represented by each size fraction is expressed as a percent of the metered dose.

4.4. Airway deposition Deposition in the respiratory tract occurs by inertial impaction and gravitational settling of the drug particles. Impaction can be significant mainly for large particles which deposit mostly in the upper and large bronchial airways during inhalation. Deposition of large particles during exhalation is usually negligible due to the lack of such particles caused

Deposited fraction (%)

50

48.7 48.0

by the intense inspiratory deposition. Drug particles smaller than 2 μm deposit mostly by gravitational settling. Practically, the higher the residence time of a particle in the airways, the higher the probability to deposit by gravity. To quantify the dose of drug depositing in the lungs in different phases of the breathing cycle we analysed the case of a fictive individual characterized by breathing parameters obtained by averaging the corresponding breathing data of the 25 volunteers (see Table 2). The total lung deposition is normalized to 100% in the left panel of Fig. 6. This panel demonstrates that most of the particles depositing in the lungs in a breathing cycle deposit during inhalation (48.7% of the total lung deposition for budesonide and 48% for formoterol) and breath-hold (48.3% of the total lung deposition for budesonide and 48% for formoterol), while deposition during exhalation is low (3% of the total lung deposition for budesonide and 4% for formoterol). This outcome emphasizes the importance of breath-hold within the inhalation manoeuvre. The instruction to hold the breath after inhalation as long as possible is often missing or not emphasized enough in the patient information leaflet (PIL). To see how exactly the duration of breathhold affects lung deposition of Symbicort® Turbuhaler® we carried out computations for the same fictive person characterized by average breathing data shown in Table 2, but with varying values of breathhold time. The right panel of Fig. 6 depicts the dose deposited in the lungs expressed as a percent of the metered dose versus the duration of breath-hold. The figure demonstrates that it is extremely important to hold the breath after inhalation for 10 s or at least a few seconds, who is not able to hold the breath for a longer period of time. No major further improvement in deposited lung dose can be obtained over 10 s of breath-hold time. This is due to the fact that most of the large particles deposit during inhalation and the remaining fraction of smaller particles (below 2 μm) is relatively limited in case of Symbicort® Turbuhaler®. For drugs with a more significant extrafine particle fraction holding the breath after the inhalation is even more important. Since both inertial impaction and gravitational sedimentation are flow rate dependent, and particle size distribution also depends on flow rate, it is expected that regional drug deposition will be highly sensitive to this parameter. To demonstrate this, individual-specific drug deposition distributions were calculated by the application of SLDM model based on the presented breathing parameters, emitted dose values and particle size distributions. Fig. 7 depicts the computed upper airway doses, lung doses and total airway doses of budesonide and formoterol for every participating individual as a function of inhalation flow rate (Q). The corresponding simulated individual-specific emitted doses are also plotted. Each computed dose is expressed as a percent of metered dose and symbols along the same (imaginary)

48.3 48.0 budesonide formoterol

40

30

20

10

3.0 4.0 0

inhalation

breath-hold

exhalation

Fig. 6. Deposited fractions of budesonide and formoterol during different phases of the breathing for a fictive individual with breathing data averaged over 25 volunteers (left panel; total lung deposition normalized to 100%) and lung deposition dependence on breath-hold time (right panel; deposited dose is expressed as a percent of the metered dose; dashed lines represent minimum mean and maximum values of breath-hold time for the 25 participating volunteers).

Á. Farkas et al. / European Journal of Pharmaceutical Sciences 93 (2016) 371–379 100

100

Emitted dose Total airway dose Lung dose Upper airway dose

90 80

Emitted dose Total airway dose Lung dose Upper airway dose

90 80

70

70

60

60

Dose (%)

Dose (%)

377

50 40 30

50 40 30

20

20

budesonide

10 0

formoterol

10 0

30

40

50

60

70

80

90

100

30

40

50

Inhalation flow rate (L/min)

60

70

80

90

100

Inhalation flow rate (L/min)

Fig. 7. Budesonide (left panel) and formoterol (right panel) emitted doses and deposited doses in the upper airways (mouth, pharynx and larynx), lungs and in the whole respiratory system of the 25 individuals expressed as percentages of the metered dose versus inhalation flow rate.

consensus that the use of Turbuhaler® is not recommended for patients with flow rates lower than 30 L/min. Wolthers (2016) has recently reviewed the world literature of the use of dry powder fixed combinations of budesonide and formoterol and stated that there is no convincing evidence for their use in children under 12 years of age and they should not be prescribed to this age group. This is in line also with the indications from the patient information leaflet. In addition to the expert opinion, current results demonstrate that children would probably receive very low doses of medication due to their lower inhalation flow rates. Besides the high intersubject variability of the deposited lung dose observed for healthy individuals, it is expected that the depositing drug dose will also exhibit a high variability for the same COPD or asthma patient in different stages of the disease according to their actual inspiratory vital capacity. Based on the results in Fig. 7 the depositing dose of the drug may decrease abruptly if the breathing performance of the patient is worsening. The high variability of the lung dose may raise questions for the medical practitioner regarding the right dosing of the medication. However, symptom driven flexible dosing is possible only in the case of asthma patients (SMART, single inhaler maintenance and reliever therapy). Since females reached lower average inhalation flow rates than males (average female flow rate: 55 L/min; average male flow rate: 75.2 L/min) it was expected that average regional deposition values of females and males were also markedly different. Fig. 8 depicts the average ICS deposition values for the extrathoracic and intrathoracic parts of the airways of females and males. A significant inter-gender difference in terms of regional depositions can be observed. Males have got higher 40 35

ET LUNG

30 25

Dose (%)

vertical line corresponding to a given flow rate value represent the doses of the same individual. The figure demonstrates a monotone increase of all the plotted quantities with the increase of the flow rate in the studied interval. The inhalation flow rate dependence seems to be close to linear, though some saturation tendency of the lung dose is observable. Naturally, at further increasing flow rate the lung dose would stop increasing and even would decrease due to the lack of particles penetrating the intrathoracic airspaces. However, such effect would manifest only at unrealistically high flow rates. More importantly, the observed high variability of the emitted dose leads to a significant variability of deposited doses as a function of inhalation flow rate. Based on our simulation results the dose deposited in the extrathoracic region (mouth, pharynx and larynx) varies from 25.7% to 39.8% (budesonide) and from 22% to 47% (formoterol), with a mean value of 32.4% of the metered dose for both components. The dose deposited in the lungs takes values between 20.4% and 48.8% (budesonide) and 16.4% and 42.9% (formoterol). Mean lung dose of the formoterol (29.8%) is lower than that of budesonide (33.6%). The observed differences between the two drug components in terms of deposition efficiency raises questions about the well-known synergistic effect of the co-depositing components of the ICS + LABA combination drugs. Numerous randomized clinical studies (e.g. Rabe et al., 2006; Kuna et al., 2007) have shown the advantages of budesonide plus formoterol therapy compared to monotherapy. A possible explanation is the enhanced anti-inflammatory activity due to the synergistic inhibitory effects on proinflammatory signaling pathways, inflammatory mediator release, and recruitment and survival of inflammatory cells (Johnson, 2004). In case of significantly different deposition efficiencies of the two components this effect would be compromised. However as the results show, different flow rate intercepts are visible when comparing lung and upper airway deposition for the two compounds. Budesonid's lung deposition is higher when reaching flow rate of about 60 L/min, while for formoterol higher lung deposition is seen below 50 L/min as compared to the upper airways. As formoterol is a rapid acting LABA, after its use bronchodilation is reached early. So if the patient is advised to take more than one inhalation the second manoeuvre might increase lung volumes and flow rate and so might generate much higher lung deposition of both drugs. Upper airway deposition is not needed in the treatment of obstructive airway diseases and is responsible for side effects especially for the ICS component. Fig. 7 demonstrates a clear disadvantage for upper airway deposition at lower flow rates (b 60 L/min) for budesonide. Although in our case only one person out of 25 had a flow rate slightly below 30 L/min, it is evident based on the tendencies depicted in Fig. 7 that both the budesonide and formoterol lung doses become marginally low at low flow rates. This is in agreement with the general

20 15 10 5 0

females

males budesonide

females

males formoterol

Fig. 8. Computed average extrathoracic (ET) and lung (LUNG) doses of budesonide and formoterol for females and males expressed as percentages of the metered dose.

378

Á. Farkas et al. / European Journal of Pharmaceutical Sciences 93 (2016) 371–379

deposition values in both regions (females budesonide: ET = 30.4%, LUNG = 29.2%; females formoterol: ET = 27.2%, LUNG = 26.4%; males budesonide: ET = 33.9%, LUNG = 37%; males formoterol: ET = 36.4%, LUNG = 32.5%). However, this computed difference observed in inter-gender variability of drug deposition was not confirmed in clinical trials. Average female lung doses shown in Fig. 8 are close to the upper limit of the measured lung doses (see Table 1) and male lung doses are even higher. This is due to the fact that the subjects of the present study were healthy adult volunteers with low average age (38 years both for females and males) with quite high average inhalation flow rates. Lung deposition values of healthy individuals of this study whose inhalation flow rates are comparable to the flow rates in the aforementioned works are in good agreement with the published values (see also Fig. 5). COPD patients may have significantly lower inhalation capacity (Azouz et al., 2015). Even more important than disease severity, elevated age may be a factor predicting lower inspiratory effort (Janssens et al., 2008; Jarvis et al., 2007). The numerical method developed and validated in this study is applicable to any adult population group. Its application to the measured breathing parameters of COPD patients with different degrees of disease severity is already in progress and it will be the subject of a next publication. The numerical procedure is also under development, with a major improvement of considering time dependent flow profile in the future, instead of describing it by the inhaled volume and inhalation time (and their ratio: Q).

5. Conclusions This study demonstrated that carefully validated computational models can successfully complement scintigraphic measurements and other methods used for the determination of airway deposition of the inhaled aerosol drugs. In addition, numerical simulations can be effective tools in personalized drug choice and in optimizing the patient specific breathing mode during the inhalation of a given aerosol drug. The models developed and applied in this work can be used for the analysis of airway deposition distribution of any other commercialized aerosol drug. Moreover, numerical modelling can be used in the development phase of drugs and inhalers and the results of simulations might be taken into account in the process of drug authorization. Present results demonstrate that deposition distribution of Symbicort® Turbuhaler® is effective in the lungs if the person is able to produce high enough inhalation flow rates. The high inter-gender and inter-individual scatter of lung deposition emphasizes the need for personalized treatment planning. As the flow rate is the most important factor for the deposition of the drugs delivered via the Turbuhaler®, it is of major importance to advise the patients to use their maximal IVC, especially if they feel the worsening of their disease. Additionally, increasing the breath hold time might contribute to better lung deposition, so this manoeuvre should be emphasized as well. As a continuation of the present work, measurement of breathing parameters, including breath-hold and exhalation times, of COPD patients with different degrees of disease severity are planned in conjunction with deposition calculations for Symbicort® Turbuhaler® and other drugs from the market.

Author disclosure statement None of the authors have shares in any pharmaceutical company. PF declares that he has no conflict of interest. ÁF, ÁJ and IB have received honoraria for presentation from Chiesi Hungary Ltd. GT and AH are full time employees of Chiesi Hungary Kft. VM had consultant arrangements with AstraZeneca, Berlin Chemie, Boehringer Ingelheim, Chiesi, GSK, Novartis, Orion, Sandoz, Sager Pharma and Takeda.

Acknowledgement This work has been supported by the KTIA_AIK_12-1-2012-0019 project.

References Abdelrahim, M.E., 2010. Emitted dose and lung deposition of inhaled terbutaline from Turbuhaler at different conditions. Respir. Med. 104, 682–689. Assi, K.H., Tarsin, W., Chrystyn, H., 2006. High performance liquid chromatography assay method for simultaneous quantitation of formoterol and budenoside in Symbicort Turbuhaler. J. Pharm. Biomed. Anal. 41, 325–328. Azouz, W., Chetcuti, P., Hosker, H.S., Saralaya, D., Stephenson, J., Chrystyn, H., 2015. The inhalation characteristics of patients when they use different dry powder inhalers. Journal of Aerosol Medicine and Pulmonary Drug Delivery 28, 35–42. Bagherisadeghi, G., Larhrib, H., Chrystyn, H., 2015. Ex-vivo study of Symbicort using inhalation profiles of patients with chronic obstructive pulmonary disease. Journal of Aerosol Medicine and Pulmonary Drug Delivery 28, A11–A12. Balásházy, I., Alföldy, B., Molnár, A.J., Hofmann, W., Szőke, I., Kis, E., 2007. Aerosol drug delivery optimisation by computational methods for the characterization of total and regional deposition of therapeutic aerosols in the respiratory system. Curr. Comput. Aided Drug Des. 3, 13–32. Balásházy, I., Horváth, A., Sárkány, Z., Farkas, Á., Hofmann, W., 2009. Simulation and minimisation of airway deposition of airborn bacteria. Inhal. Toxicol. 21, 1021–1029. Borgström, L., Newman, S., 1993. Total and regional lung deposition of terbutaline sulfate inhaled via a pressurized MDI or via Turbuhaler®. Int. J. Pharm. 97, 47–53. Borgström, L., Asking, L., Lipniunas, P., 2005. An in vivo and in vitro comparison of two powder inhalers following storage at hot/humid conditions. Journal of Aerosol Medicine 18, 304–310. Borgström, L., Bondesson, E., Morén, F., Trofast, E., Newman, S.P., 1994. Lung deposition of budesonide inhaled via Turbuhaler®: a comparison with terbutaline sulphate in normal subjects. Eur. Respir. J. 7, 69–73. Borgström, L., Derom, E., Stahl, E., Wahlin-Boll, E., Pauwels, R., 1996. The inhalation device influences lung deposition and bronchodilating effect of terbutaline. Am. J. Respir. Crit. Care Med. 153, 1636–1640. Burnell, P.K.P., Small, T., Doig, S., Johal, B., Jenkins, R., Gibson, G.J., 2001. Ex-vivo product performance of Diskus® and Turbuhaler® inhalers using inhalation profiles from patients with severe chronic obstructive pulmonary disease. Respir. Med. 95, 324–330. Buttini, F., Brambilla, G., Copelli, D., Sisti, V., Balducci, A.G., Bettini, R., Pasquali, I., 2016. Effect of flow rate on in vitro performance of NEXThaler® in comparison with Diskus® and Turbohaler® dry powder inhalers. Journal of Aerosol Medicine and Pulmonary Drug Delivery 29, 167–178. Chrystyn, H., Safioti, G., Keegstra, J.R., Gopalan, G., 2015. Effect of inhalation profile and throat geometry on predicted lung deposition of budesonide and formoterol (BF) in COPD: an in-vitro comparison of Spiromax with Turbuhaler. Int. J. Pharm. 491, 268–276. Corradi, M., Chrystyn, H., Cosio, B.G., Pirozynski, M., Loukides, S., Louis, R., Spinola, M., Usmani, O.S., 2014. NEXThaler, an innovative dry powder inhaler delivering an extrafine fixed combination of beclometasone and formoterol to treat large and small airways in asthma. Expert Opinion on Drug Delivery 11, 1497–1506. Council of Europe, 2014. European Pharmacopoeia. 8th ed. http://www.edqm.eu/en/ european-pharmacopoeia-8th-edition-1563.html. de Boer, A.H., Gjaltema, D., Hagedoorn, P., Frijlink, H.W., 2015. Can ‘extrafine’ dry powder aerosols improve lung deposition? Eur. J. Pharm. Biopharm. 96, 143–151. de Boer, A.H., Hagedoorn, P., Gjaltema, D., Goede, J., Frijlink, H.W., 2005. Air classifier technology (ACT) in dry powder inhalation. Part 4: performance of air classifier technology in the Novolizer dry powder inhaler. Int. J. Pharm. 310, 81–89. Farkas, Á., Balásházy, I., 2015. Development and application of a complex numerical model and software for the computation of dose conversion factors for radon progenies. Radiat. Prot. Dosim. 164, 268–290. Farkas, Á., Jókay, Á., Balásházy, I., Füri, P., Müller, V., Odler, B., Horváth, A., 2015. Computer modelling as a tool in characterization and optimization of aerosol drug delivery. Aerosol Air Qual. Res. 15, 2466–2474. Feddah, M.R., Brown, K.F., Gipps, E.M., Davies, N.M., 2000. In-vitro characterisation of metered dose inhaler versus dry powder inhaler glucocorticosteroid products: influence of inspiratory flow rate. J. Pharm. Pharm. Sci. 3, 318–324. Gjaltema, D., Hagedoorn, P., Frijlink, H.W., de Boer, A., 2014. Are extra-fine particles from dry powder inhalers likely to improve lung deposition? Eur. Respir. J. 44 (Suppl. 58), P909. Haefeli-Bleuer, B., Weibel, E.R., 1988. Morphometry of the human pulmonary acinus. Anat. Rec. 220, 401–414. Haikarainen, J., Happonen, A., Loytana, T., 2015. In vitro comparison of dose accuracy of two budesonide/formoterol dry powder inhalers. Eur. Respir. J. 46. http://dx.doi. org/10.1183/13993003.congress-2015.PA2953. Hirst, P.H., Bacon, R.E., Pitcairn, G.R., Silvasti, M., Newman, S.P., 2001. A comparison of the lung deposition of budesonide from Easyhaler, Turbuhaler and pMDI plus spacer in asthmatic patients. Respir. Med. 95, 720–727. Hofmann, W., Morawska, L., Bergmann, R., 2001. Environmental tobacco smoke deposition in the human respiratory tract: differences between experimental and theoretical approaches. Journal of Aerosol Medicine 14, 317–326. Hoppentocht, M., Hagedoorn, P., Frijlink, H.W., de Boer, A.H., 2014. Technological and practical challenges of dry powder inhalers and formulations. Adv. Drug Deliv. Rev. 75, 18–31.

Á. Farkas et al. / European Journal of Pharmaceutical Sciences 93 (2016) 371–379 Horváth, A., Balásházy, I., Farkas, Á., Sárkány, Z., Hofmann, W., Czitrovszky, A., Dobos, E., 2011. Quantification of airway deposition of intact and fragmented pollens. J. Environ. Health Res. 21, 427–440. Janssens, W., VandenBrande, P., Hardeman, E., de Langhe, E., Philps, T., Troosters, T., Decramer, M., 2008. Inspiratory flow rates at different levels of resistance in elderly COPD patients. Eur. Respir. J. 31, 78-32. Jarvis, S., Ind, P.W., Shiner, R.J., 2007. Inhaled therapy in elderly COPD patients; time for re-evaluation? Age Ageing 36, 213–218. Johal, B., Howald, M., Fischer, M., Marshall, J., Venthoye, G., 2013. Fine particle profile of fluticasone propionate/formoterol fumarate versus other combination products: the DIFFUSE study. Comb. Prod. Ther. 3, 39–51. Johnson, M., 2004. Interactions between corticosteroids and b2-agonists in asthma and chronic obstructive pulmonary disease. Proc. Am. Thorac. Soc. 1, 200–205. Jókay, Á., Farkas, Á., Füri, P., Horváth, A., Tomisa, G., Balásházy, I., 2016. Computer modelling of airway deposition distribution of Foster® NEXThaler® and Seretide® Diskus® dry powder combination drugs. Eur. J. Pharm. Sci. 88, 210–218. Kamin, W.E.S., Genz, T., Roeder, S., Scheuch, G., Trammer, T., Jeunemann, R., Cloes, R.M., 2002. Mass output and particle size distribution of glucocorticosteroids emitted from different inhalation devices depending on various inspiratory parameters. Journal of Aerosol Medicine 15, 65–73. Koblinger, L., Hofmann, W., 1990. Monte Carlo modelling of aerosol deposition in human lungs. Part 1. Simulation of particle transport in a stochastic lung structure. J. Aerosol Sci. 21, 661–674. Kuna, P., Peters, M.J., Manjra, A.I., Jorup, C., Naya, I.P., Martinez-Jimenez, N.E., Buhl, R., 2007. Effect of budesonide/formoterol maintenance and reliever therapy on asthma exacerbations. Int. J. Clin. Pract. 61, 725–736. Lahelma, S., Kirjavainen, M., Kela, M., Herttuainen, J., Vahteristo, M., Silvasti, M., RankiPesonen, M., 2005. Equivalent deposition of budesonide in vivo: a comparison of dry powder inhalers using a pharmacokinetic method. Br. J. Clin. Pharmacol. 59, 167-163. Martin, G.P., Mariott, C., Zeng, X.M., 2007. Influence of realistic inspiratory flow profiles on fine particle fractions of dry powder aerosol formulations. Pharm. Res. 24, 361–369. Meakin, B.J., Cainey, J.M., Woodcock, P.M., 1995. Drug delivery characteristics of Brycanil Turbuhaler. Miller, M.R., Hankinson, J., Brusasco, V., Burgos, F., Casaburi, R., Coates, A., Crapo, R., Enright, P., van der Grinten, C.P.M., Gustafsson, P., Jensen, R., Johnson, D.C., MacIntyre, N., McKay, R., Navajas, D., Pedersen, O.F., Pellegrino, R., Viegi, G., Wanger, J., 2005. Standardisation of spirometry. Eur. Respir. J. 26, 319–338. Munzel, U., Marschall, K., Fyrnys, B., Wedel, M., 2005. Variability of fine particle dose and lung deposition of budesonide delivered through two multidose dry powder inhalers. Curr. Med. Res. Opin. 21, 827–833. Nadarassan, D.K., Assi, K.H., Chrystyn, H., 2010. Aerodynamic characteristics of a dry powder inhaler at low inhalation flows using mixing inlet with an Andersen cascade impactor. Eur. J. Pharm. Sci. 39, 348–354.

379

Newman, S.P., Morén, F., Trofast, E., Talaee, N., Clarke, S.W., 1991. Terbutaline sulphate Turbuhaler: effect of inhaled flow rate on drug deposition and efficacy. Int. J. Pharm. 74, 209–213. Newman, S.P., Pitcairn, G.R., Hirst, P.H., Bacon, R.E., O'Keefe, E., Reiners, M., Hermann, R., 2000. Scintigraphic comparison of budesonide deposition from two dry powder inhalers. Eur. Respir. J. 16, 178–183. Pitcairn, G., Reader, S., Pavia, D., Newman, S., 2005. Deposition of corticosteroid aerosol in the human lung by Respimat® Soft Mist™ inhaler compared to deposition by metered dose inhaler or by Turbuhaler® dry powder inhaler. Journal of Aerosol Medicine 18, 264–272. Rabe, K.F., Atienza, T., Magyar, P., Larsson, P., Jorup, C., GLalloo, U., 2006. Effect of budesonide combination with formoterol for reliever therapy in asthma exacerbations: a randomised controlled, double-blind study. Lancet 368, 744–753. Ross, D.L., Schultz, R.K., 1996. Effect of inhalation flow rate on the dosing characteristics of dry powder inhaler (DPI) and metered dose inhaler (MDI) products. Journal of Aerosol Medicine 9, 215–226. Salma, I., Füri, P., Németh, Z., Balásházy, I., Hofmann, W., Farkas, Á., 2015. Lung burden and deposition distribution of inhaled atmospheric urban ultrafine particles as the first step in their health risk assessment. Athmos. Environ. 104, 39–49. Stahlhofen, W., Rudolf, G., James, A.C., 1989. Intercomparison of experimental regional aerosol deposition data. Journal of Aerosol Medicine 2, 285–308. Tamura, G., Sakae, H., Fujino, S., 2012. In vitro evaluation of dry powder inhaler devices of corticosteroid preparations. Allergol. Int. 61, 149–154. Tarsin, W., Assi, K.H., Chrystyn, H., 2004. In vitro intra- and inter-inhaler flow rate-dependent dosage emission from a combination of budesonide and formoterol in a dry powder inhaler. Journal of Aerosol Medicine 17, 25–32. Tarsin, W.Y., Pearson, S.B., Assi, K.H., Chrystyn, H., 2006. Emitted dose estimates from Seretide® Diskus® and Symbicort® Turbuhaler® following inhalation by severe asthmatics. Int. J. Pharm. 316, 131–137. Thorsson, L., Kenyon, C., Newman, S.P., Borgström, L., 1998. Lung deposition of budesonide in asthmatics: a comparison of different formulations. Int. J. Pharm. 168, 119–127. United States Pharmacopeia, 2014. USP 38-NF 33. Warren, S., Taylor, G., Smith, J., Buck, H., Parry-Billings, M., 2002. Gamma scintigraphic evaluation of a novel dry powder inhaler using a validated radiolabelling technique. Journal of Aerosol Medicine 15, 15–25. Weuthen, T., Roeder, S., Brand, P., Müllinger, B., Scheuch, G., 2002. In vitro testing of two formoterol dry powder inhalers at different flow rates. Journal of Aerosol Medicine 15, 297–303. Wildhaber, J.H., Devadason, S.G., Wilson, J.M., Roller, C., Lagana, T., Borgström, L., Le Souef, P.N., 1998. Lung deposition of budesonide from Turbuhaler in asthmatic children. Eur. J. Pediatr. 157, 1017–1022. Wolthers, O.D., 2016. Budesonide + formoterol fumarate dehydrate for the treatment of asthma. Expert. Opin. Pharmacother. 17, 1023–1030.