Prof. Dr. Henderik W. Frijlink

Transcription

1 Pulmonary drug administration technologies to improve the therapy in Asthma, COPD and beyond. Prof. Dr. Henderik W. Frijlink Department of Pharmaceutical Technology and Biopharmacy University of Groningen founded in 1614

2 2 Content The basics of pulmonary drug administration Dry powder inhalers: new insights in powder formulations and powder dispersion into an aerosol Beyond asthma and COPD: new therapies applying the pulmonary route of drug administration via the Twincer inhaler

3 (%) The basics of drug inhalation The efficacy of inhaled drugs is determined by a combination of: penetration of aerosolized particles into the airways deposition of these particles on the mucus Upper throat deposition Only particles within the 1 5 µm size range are able to penetrate into the deeper airways and deposit there Sedimentation Diffusion and exhalation penetration / deposition Penetration in target area Deposition Preferred particle size aerodynamic part. diameter ( m m)

4 percent of real dose (%) What is the optimal size of the aerosol? Mono-disperse aerosols of different particle size ( μm) Inhaled at different inhalation flow rates 31 and 67 l/min) exhaled oropharynx central + intermediate peripheral micron 3.0 micron 6.0 micron flow rate (l/min) Aerodynamic diameter: μm From Usmani et al., AJRCCM 2005, Re-calculated by A.H.de Boer (Groningen)

5 % exhaled/settling time (s) Are smaller particle sizes of the aerosol better? % exhaled at 31 L/min % exhaled at 67 L/min settling time (s) particle diameter (µm) From Usmani et al., AJRCCM 2005, Re-calculated by A.H.de Boer (Groningen) No: At particle sizes below 1 mm exhalation > 50% Because settling times of these small particles will be over 10 seconds

6 12 Inhaler development philosophy Good performance of an inhaler can only be achieved upon adequate balancing of the three major forces involved Formulation Device Patient surface tension or interparticular forces Break-up or deagglomeration forces during inhalation deposition forces in the human lungs

7 Systems for pulmonary drug administration Objectives: To generate at the right moment an aerosol of the preferred particle size distribution and containing the adequate dose. Moment: at the start of the inhalation (<2 l) Particle size: 1-5 mm Dose: 4 mg 400 mg Prevent high inhalation flow rates Increase the duration of the inhalation cycle Simple and fast (<1 min) administration 13

8 14 percent deposition (%) depositiefractie Prevent high inhalation flow rates µm particles higher airways lower airways 0,12 0,10 0,08 0,06 12 L/min 42 L/min 60 L/min 40 0,04 0, , luchtweg generatie Inhalation flow rate (l/min) Data from Byron, Respiratory Drug Delivery, 1990, The deposition in the lower airways is strongly reduced at increased inhalation flow rates (more forceful inhalation)

9 15 The duration of the inhalation cycle and breath-hold Deposition fraction in the target area (deeper airways) by sedimentation Particles of 1 µm * Mean airway diameter in generations ( mm) T = 0 *Normalised lung volume 1 liter 4.2 l in 6 l lung volume Distance fallen 3 s Distance fallen 6 s from Byron, Respiratory Drug Delivery, 1990

10 16 Inhalation systems Jet and ultrasonic nebulizers Metered dose inhalers (with spacers) Dry powder inhalers: dpi s Soft mist inhalers Pari LC Sprint Flixotide MDI Respimat Genuair

11 Dry powder inhaler (DPI) Breath-controlled, breath-actuated 30 to 40 % (deep) lung deposition possible No propellant, minimal use of excipients? Stable formulations possible For processing agglomerated particles required In the aerosol de-agglomerated particles required Formulation difficult 17

12 What makes a good dry powder inhaler An increasing fine particle dose with increasing flow rate A medium to high air flow resistance A high delivered fine particle dose (FPD) preferably between 1.5 and 3 µm Minimal inter-dose, -device and batch-tobatch variation A robust design, easy to use 18

13 19 Functional parts of a DPI Mouthpiece Powder disperson system (disintegration principle) Powder formulation Dose measuring system Or preloaded cartidges

14 Powder formulations for particles of 2-5 mm 20 Soft spherical pellets Micronized drug cohesive forces instable good de-agglomeration adhesive mixtures Micronized drug with (larger) carrier crystals adhesive and cohesive forces stable systems Difficult deagglomeration

15 21 Understanding DPI performance Return to basic philosophy The functionality of a DPI is reached via an adequate balancing between: Co- and adhesion forces in the powder Disintegration forces Long deposition forces Powder mixture Inhaler design Patient

16 Simple model: energy ratio 2/27/ Energy Binding energy (E b ): energy required for detachment Separation energy (E s ): energy put into separation of the drug particle during inhalation Energy ratio: E s /E b if 1, then detachment occurs 22

17 Energy ratio for individual drug particles Binding energy (incl. binding to apparent carrier surface sites ) From: Hickey et al, J. Pharm. Sci. 96 (2007) Susceptibility to separation energy Carrier surface site activity (inversely proportional to energy ratio) 23 From: De Boer et al, Int. J. Pharm. 260 (2003)

18 24 Cum. drug mass (%) Energy ratio distributions may help to understand and explain (principle) 100 Drug detached (low flow rate) Drug detached (high flow rate) 0 1 Energy ratio (E s /E b )

19 Adhesive mixtures for inhalation: How to study the model? Carrier residue Process variables Mixing time Mixing intensity Mixing principle Mixture variables Drug load Drug agglomeration Drug detached Component variables Type of drug Drug content Carrier size fraction (Added) lactose fines or other excipients 25 Inhalation variables Flow rate Dispersion principle

20 A model including the basic variables and interactions 26 De Boer et al., Advanced Drug Delivery Reviews, 2012 (64),

21 27 Methods: A practical approach Design a simple model/method to measure (1) drug detachment and (2) carrier residue: test inhaler Study the effects of formulation variables such as drug content-lactose types-excipients-etc. Study the effect of process variables: mixing time-mixing forces-etc. Measure the effects at different separation energies: vary with flow rates

22 28 Methods: the test inhaler F c De-agglomeration based on impaction forces, optimal use of inhalation energy Release based on separation by size F d carrier with attached drug detached drug Drug on the carrier remains in the cyclone chamber: carrier residue Detached drug will leave the cyclone chamber

23 Drug detached (%) What s the effect of mixing time? n = 5 60 So there is no straightforward answer! it depends min 420 min 0.5 min 420 min 0.5 min 420 min 0.5 min 420 min 0.5 min 420 min SX; coarse; 20 L/min FP; coarse; 20 L/min SX; fine; 20 L/min SX; coarse; 60 L/min SX; fine; 60 L/min 29 SX: salmeterol xinafoate, FP: fluticason propionate

24 Drug detached (%) What s the effect of drug content? 100 n = it depends 0.4% 4% 0.4% 4% 0.4% 4% 0.1% 0.4% 10 min; 20 L/min 10 min; 40 L/min 2 min; 20 L/min 10 min; 20 L/min 30 BUDESONIDE

25 31 Drug detached (%) What s the effect of added fine lactose? n = cause Can t it depends tell, 0% 4% 0% 4% 0% 4% 0% 4% 0% 4% Fine; 0.4%Bud 20 L/min Fine; 0.4%Bud 50 L/min Coarse; 0.4%Bud 20 L/min Fine; 4%Bud 20 L/min Fine; 4%Bud 50 L/min

26 32 Cum. drug mass (%) Energy ratio distributions may help to understand and explain (a change in formulation) 100 Positive effect on drug detachment at low flow rate No effect on drug detachment at intermediate flow rate Negative effect on drug detachment at high flow rate 0 1 Energy ratio (E s /E b )

27 Drug detached (%) Drug detached (%) The effect of mixing time %, 2 minutes 0.4%, 2 0.4%, minutes 2 minutes 4%, 60 minutes 0.4%, 600.4%, minutes 60 minutes Flow Flow rate rate (L/min) (L/min) Airbag effect 33 Salbutamol sulphate on lactose µm, testinhaler C-VI

28 Turbula Blender 90 RPM, 10 min. Carrier lactose: µm 34 The effect of drug content

29 The role of (lactose) fines Presumed roles Occupation of active carrier sites Filling up of surface discontinuities Co-agglomeration with drug particles Buffer between colliding carrier particles 35 What is a fine? At what size is a fine a fine? Do all fines five the same effects at all drug loads?

30 Effect of size of the fines Budesonide: X 50 = 1.48 μm Lactose fines coarse : X 50 = 3.78 μm Lactose fines fine : X 50 = 1.52 or 2.00 μm Lactose carrier: μm Drug load: 4% coarse fines fine fines 36

31 SEM: for explanation After inhalation without fines + 4% w/w coarse lactose fines coarse fines: No break-up of agglomerated drugs and no press-on forces % w/w fine lactose fines fine fines: Distribution of agglomerated drugs and press-on forces

32 Effect of size of the fines: effect of payload Budesonide: X 50 = 1.48 μm Lactose fines coarse : X 50 = 3.78 μm Lactose fines fine : X 50 = 2.00 μm Lactose carrier: μm Drug load: 0,4% coarse fines fine fines 38

33 Adhesive mixtures for inhalation: Try to understand the interactions! Lactose Carrier residue Component variables Type of drug Drug content Carrier size fraction (Added) lactose fines 39 + Process variables Mixing time Mixing intensity Mixing principle Inhalation variables Flow rate Dispersion principle INTERACTIONS! Fine Particle Fraction (FPF) Detached drug

34 40 Conclusions from powder studies Multi-order interactions omnipresent. Their understanding crucial for mixture optimisation Developing or optimizing techniques to measure relevant mixture properties is probably the most important challenge in the near future

35 SEM and CARS: for explanation Coherent anti-stokes Raman scattering (CARS): SEM: 41 Andrew L. Fussell Herman Offerhaus Scale bar: 20 µm

36 The role of additives Various additives found in literature: Lactose fines force control agents Purpose: magnesium stearate, l-leucine, etc. Occupation/inactivation of active sites Change the apparent payload Change (reduce) the co- and adhesive forces Protect drug particles from press-on forces during mixing 42

37 A model including the basic variables Additives 43 De Boer et al., Advanced Drug Delivery Reviews, 2012 (64),

38 Effect of force control agents Lactose Process A: smoothed lactose Process B: smoothed lactose with Mg-Stearate (0,25%) Mixtures with beclomethason dipropionate (0.8%) AFM: force of adhesion (separation energy) FPF (60 l/min) From: Young et al, J. Pharm. Pharmacol., 2002, 54,

39 Additives may interfere at the level of Adhesion forces between drug and carrier: Increases FPF Cohesion forces between the drug particles: May decrease FPF but on the other hand reduce aerosol particle size The mixing process: Increase or decrease the FPF (increase or decrease press-on forces) affect re-distribution etc. The inhalation process: Increasing or decreasing detachment forces (seperation energy) increasing or decreasing FPF 45

40 Generation of the aerosol in a DPI: a balance between binding forces and de-agglomereation forces moderate good poor Powder formulation Desintegration principe 46 Binding forces: v.d. Waals forces surface irregularities impurities capillaire forces electrostatic forces De-agglomeration forces: shear and friction forces Drag and lift forces Impaction forces

41 Forces for de-agglomeration Friction forces Drag and lift forces Inertial forces Single particles Agglomerates 47 Inertial forces largest (sponge with water) Can we apply these forces?

42 The DPI problem: dispersion of agglomerates using energy from air De-agglomeration of cohesive powders in 1-3 mm aerosols? 48 Shear forces Turbulent air Moving capsule Impaction forces

43 The fine particle fraction as function of the inhalation flow rate 49 Inhalers that generate a FPF that is dependent on the inhalation flow rate. Inhalers that generate a FPF that is independent from the inhalation flow rate.

44 50 percent deposition (%) The effect of high inhalation flow rates higher airways lower airways Inhalation flow rate (l/min) Data from Byron, Respiratory Drug Delivery, 1990, The deposition in the upper airways (throat) is strongly increased at increased inhalation flow rates (more forceful inhalation)

45 51 Fine particle fraction [%] Constant lung-dose because of inhalation flow dependent FPF generation 50 Fine particle fraction at different inhalation flows Novolizer Diskus flow [ln/min] To compensate for the increased loss by oropharyngeal impaction at increased flow rates the fine particle dose must increase to keep the lung dose constant

46 fijne deeltjesfractie [%] dose The idea behind the fow dependent DPI lungdose FPF rel. throath deposition rel. lungdeposition The increase in FPF at increasing inhalation flow results in a constant lung dose 52 inhalation fl;ow Fijne deeltjesfractie als functie van het inhalatiedebiet flow rate [l/min]

47 Deposition [%] Constant lung-dose because of inhalation flow dependent FPF generation percent of nominal dose (%) percent of nominal dose (%) Periferal lung deposition upper airways cental and peripheral Novolizer pressure drop (kpa) Inhalation flow PIFR [L/min] From: Newman et al., Eur. Respir. J., 2000,16, Diskus upper airways central and peripheral pressure drop (kpa)

48 Long depositie [% van de totale lichaamsdosis] Lung deposition from Turbuhaler in children Oropharyngeal deposition [% of total body deposition] lung deposition of budesonide with Turbuhaler throath deposition of budesonide with Turbuhaler years 9-12 years years years 9-12 years years 54 From: Devadason SG, et al., Eur Respir J Sep;10(9):

49 The importance of good inhalation devices Serum levels (% van C max ) of formoterol after inhalation via: (n=29) Cyclohaler Novolizer Pulmonary Oral absorption Pulmonary Oral absorption From: 55 Petzold et al., J Aerosol Med Pulm Drug Deliv Sep;21(3):

50 The Twincer : A disposable DPI for high powder doses Highly efficient de-agglomeration: Varying doses up to 60 mg in one inhalation (two diametrically placed cyclones) Flexible application: large industry to SME Do it yourself inhaler (weigh-seal-click) Disposable: Infections (originally Cystic Fibrosis) Single use (e.g. vaccination, emergencies, offperiods etc) Cheap: Only three parts of plastic and a blister (or a cover foil) Complete moisture protection Simple to use 56

51 Simple to use Remove cover foil Inhale Dispose inhaler (disposable, recyclable plastic) 57

52 58 Computational fluid dynamics and computational particle tracking Calculate air flow rate Inlet powder channel Inlet classifier bypass Inlet bypass level 2 Calculate particle residence time Passage of 1 μm particles Passage of 10 μm particles Retention of carrier particles

53 Efficient aerosol generation of doses up to 60 mg per inhalation percent in class (%) Different doses of colistin sulfomethate were aerosolized, and the particle size distribution of the aerosol was determined Even at 60 mg the size distribution of the aerosol is only marginally changed compared to 25 or 8 mg powder doses dose is 8 mg dose is 25 mg dose is 60 mg 4 0 0, upper class limit (µm)

54 60 Twincer dispersion efficiency Aerosol: particle size, flow rate, indication Sustainability/robustness of device: pollution, wear, price Contamination, complexity, ease of use, patient abilities Use of battery, etc. System l/min X 50 (mm) Rel. width X90-X10 Pulmicort mdi (CFC) QVAR mdi (HFA) Pari LC Plus Soft mist: Pari eflow Soft mist: Respimat Soft mist: Handspray DPI: Twincer (25 mg dose) X50

55 Examples of new dry powder inhalation therapies: current studies in man Colistimethate in cystic fibrosis Tuberculosis: Colistimethate Kanamycin Tobramycin in bronchiectasis: Levodopa in Parkinson s disease Adenosine as bronchial provocation agent 61 Influenza vaccination

56 Colistimethate-Twincer studies in CFpatients 10 patients Inhaler: Twincer : Colistin sulphomethate 25 mg (2x12.5 mg) 16.7% sweeper lactose X 10 : 0.7 mm, X 10 : 1.6 mm, X 90 : 3.1 mm Nebulizer (Ventstream -PortaNeb ): 158 mg colistin sulphomethate solution Pulmonary function tests: FEV 1 and FVC Breathhold: 2-3 sec Questionnaire 62

57 Colistimethate-Twincer studies in CFpatients II 23 mg Relative bioavailability compared to nebulizer: % 160 mg per neb. = 55 mg per DPI Patient satisfaction score: 9 excellent positive 1 good mg 4 patients mild cough with both administrations Extremely robust performance of the Twincer : Inhalation profile Particle size of powder Breath hold

58 Robustness of the Twincer 10 patients Inhaler: Twincer : 64 Colistin sulphomethate 25 mg (2x12.5 mg) 16.7% sweeper lactose X 10 : 0.7, X 50 : 1.6, X 90 : 3.1 mm PIF through inhaler: 67.9 l/min ( ) Breathhold: 2-3 sec Relative Nebulizer bioavailability: (Ventstream- PortaNeb): Rel. complete dose: 270% Rel. 158 mg emitted colistin dose: solution 140% CPulmonary function tests: max : 66.3 μg/ml (41-91) FEV 1 and FVC t max : 0.86 h ( ) 7 patients Inhaler: Twincer : Colistin sulphomethate 25 mg (2x12.5 mg) 16.7% sweeper lactose X 10 : 0.9, X 50 : 2.1, X 90 : 3.8 mm PIF through inhaler: 43.9 l/min ( ) Breathhold: >7 sec Nebulizer Relative bioavailability: (Ventstream- PortaNeb): Rel. complete dose: 300% 158 Rel. mg emitted colistin dose: solution 140% Pulmonary C function tests: max : 62.7 μg/ml (38-87) FEV 1 and FVC t max : 0.74 h ( )

59 Tuberculosis: The rapid development of MDR and XDR TB Tuberculosis, pulmonary bacterial infection: 1.7 billion carriers of latent TB Rapid growth of multi-drug en extremely drug resistant TB new MDR-TB cases per year 1 out of 2 MDR-TB patients dies form the disease , 9728, 2010, Proportion of multidrug-resistant disease among (A) new cases and (B) previously treated cases of tuberculosis Based on Global Drug Resistance Surveillance Project data.19 and 32 Australia, Democratic Republic of the Congo, Fiji, Guam, New Caledonia, Solomon Islands, and Qatar reported data for combined new and previously treated cases.

60 The size of the MDR en XDR-TB problem World: 9 million new TB patients per year ( MDR-TB) Bejing (18 MM inhabitants) 500 new patients with MDR-TB per month Survival after sputum collection in patients with XDR tuberculosis Kaplan-Meier survival curve depicting the rapid mortality among 52 of 53 patients with XDR tuberculosis and confirmed dates of death in an outbreak in a rural area in KwaZulu-Natal, South Africa. 66

61 Reasons to treat MDR and XDR TB with inhaled antibiotics 1. To obtain a high concentration at the infection site in the lungs: Resistant strains are 10 times less sensitive to the antibiotic, so an over 10 times higher drug concentration might be interesting Reduced systemic exposure may reduce side-effects and allow higher dosing 2. Reduction of transmission 3. Prevent the development of new resistant strains 4. Compared to injection inhalation: Is cheaper and easier Non-invasive Requires no medically trained personnel, only for instruction Has no transmission risks from disposed needles 67

62 air velocity (m/s) A reduced chance of transmission? Transmission of the disease occurs via airborne TB containing droplets generated during cough The source of the TB containing aerosol is the mucus in the conducting airways from which the infected droplets are entrained l/min 60 l/min 90 l/min airway generation

63 Inhaled colistimethate in the treatment of MDR-tuberculose TB exposure stopped to Animal Rooms Guinea Pig Cohort Receiving Aerosols from TB Ward A B A B B A B A A B A B B A B A Inhaled Administration to TB Patients ST only ST + IA ST only ST + IA ST + IA ST only ST + IA ST only ST only ST + IA ST only ST + IA ST + IA ST only ST + IA ST only Infectious Patient Group 1 Patient Group 2 Patient Group 3 Patient Group 4 Source TST-1 TST-2 TST-3 TST-4 TST-5 TST-6 Table 1: A schematic of key events during the course of the proposed study. Six MDR-TB patients, forming a patient group, will provide the infectious aerosols to expose susceptible guinea pigs in the study. Each Patient Group is required to remain in the TB Ward of the AIR facility for four weeks, after which a new set of 6 patients will be admitted. There are most 4 patient 24 patiënts 2 weeks treatment 3x daily 25 mg inhaled colistimethate groups recruited over the course of four months. After the Patient Group 4 is discharged from the study, only activities regarding the guinea pigs are maintained. Tuberculin Skin Tests are adminsitered to guinea pigs at six time points: before start of the study, at 4, 8, 12, 16, and finally 20 weeks. Air from the ward is directed to Guinea Pig Cohort A when patients are on as add-on therapy to standard therapy systemic therapy (ST) alone, while air is directed to Guinea Pig Cohort B when patients are receiving an inhaled antimicrobial (IA) on top of systemic therapy. 69

64 70 How to measure transmission AIR, Experimental Plan Guinea Pig Air Sampling A B Guinea Pig TB RFLP Odd days Even days UVGI or other intervention 3 patient rooms Plus common areas Intervention on/off on alternative days Pt. TB RFLP

65 Results so far: Guinea pig infections per cohort: control group intervention group Total: % reduction in transmission Significant reduction in mucosal TB Furture: 71 New study: 3x daily inhalation of 50 mg colistimethate Kanamycin inhaled via the Cyclops inhaler (Twincer variant)

66 Influenza and the vaccine Problems related to the flu vaccination: Vaccine (HA) is instable Aqueous suspension: 6-12 months at 4-10 C Fear for the needle (15-35%) Injected vaccine is effective in only 50-70% of the population over 65 year old Current vaccination does not protect against drifted and shifted influenza strains (yearly vaccination required) Medically trained personal necessary for administration Inhalation administers the vaccine via the natural route of infection Needle free Self-administration possible An immune response at the site of infection (mucosal immunity in the airways) No adjuvants needed 72

67 Particle engineering for the production of a stable inulin based powder with subunit vaccine September 15, 2010 at 10:13 AM Spray-freeze dried particles Vaccine 3 months 3 years Liquid vaccine (4 ºC) 100% <5% Powder spray dried (20 ºC) 100% 100% Powder spray freeze dried (20 ºC) 100% 97% Spray dried particles PATH grant aims to improve shelf life of pandemic flu vaccines By Kristi Heim Seattle global health nonprofit PATH received a $5.2 million contract from the federal government to develop stable pandemic influenza vaccines, which could help extend the shelf life and stockpile more of the vaccine. The contract from the Biomedical Advanced Research and Development Authority (BARDA), a division of the US Department of Health and Human Services, could lead to an additional $4.2 million in funding from BARDA in the project's second phase. 73 J. Contr. Rel., 144, , 2010

68 Vaccine, 25, , Pulmonary administration of inulin stabilized influenza vaccine powder to mice Balb/c mice, subunit A/Panama/2007/99 vaccine (H3N2) Vaccine administrations: Intramuscular: 5 ug vaccine Intrapulmonary: 5 ug vaccine as liquid Intrapulmonary: 5 ug vaccine as inulin stabilized powder Prime + two boosters: day 0, 14 and 28 Systemic immune response at day 42: 10 log serum-igg titer intra aerosol powder muscular inhalation inhalation * 2 log HI titer * p<0.01 intra aerosol powder muscular inhalation inhalation i.m a.i. p.i.

69 75 Pulmonary administration of inulin stabilized influenza vaccine powder to mice Mucosal immune response: Nose Lung 10 log Ig titer IgG IgA 1/8 5/8 2/8 *p<0.05 6/8 * p<0.01 7/8 * p<0.001 * p<0.001 Intra i.m. aerosol a.i powder p.i. muscular inhalation inhalation Conclusions: Improved immune response in mice compared to intramuscular administration: Systemic and mucosal response (incl. IgA) Cross protection against drifted virus variants Protection at the port of entry of the virus Pulmonary influenza vaccination requires no adjuvant Non-invasive administration

70 J. Contr. Rel., 144, , 2010 Step into humans Successful studies date already 40 years back! Influenza antibody response following aerosal administration of inactivated virus. Waldman RH, Wood SH, Torres EJ, Small PA Jr. Am J Epidemiol Jun;91(6): Immunization against influenza. Prevention of illness in man by aerosolized inactivated vaccine. Waldman RH, Mann JJ, Small PA Jr. JAMA Jan 20;207(3): A comparative trial of influenza immunization by inhalation and hypojet methods. Haigh W, Howell RW, Meichen FW. Practitioner Sep;211(263): spray-freeze dried and spray dried powders from the Twincer Cascade impactor results 76

71 77 The Twincer : inhalation of 50 mg colistin sulfomethate

72 Thanks Floris Grasmeijer Anne H. de Boer 78 Literature: Grasmeijer F, Hagedoorn P, Frijlink HW, de Boer AH. Drug content effects on the dispersion performance of adhesive mixtures for inhalation. PLoS One Aug 14;8(8):e doi: /journal.pone ecollection Grasmeijer F, Hagedoorn P, Frijlink HW, de Boer HA. Mixing time effects on the dispersion performance of adhesive mixtures for inhalation. PLoS One Jul 2;8(7):e doi: /journal.pone Print 2013 Grasmeijer F, Lexmond AJ, van den Noort M, Hagedoorn P, Hickey AJ, Frijlink HW, de Boer AH. New Mechanisms to Explain the Effects of Added Lactose Fines on the Dispersion Performance of Adhesive Mixtures for Inhalation PLoS ONE 9(1): e doi: /journal.pone Grasmeijer F, Frijlink HW, de Boer AH. A proposed definition of the activity of surface sites on lactose carriers for dry powder inhalation. Eur J Pharm Sci Submitted de Boer AH, Chan HK, Price R. A critical view on lactose-based drug formulation and device studies for dry powder inhalation: which are relevant and what interactions to expect? Adv Drug Deliv Rev Mar 15;64(3):257-74

73 79 That s a great question!! Come to think of it, I m not sure what it is I m trying to tell you Questions