Airway Deposition and Clearance and Systemic Pharmacokinetics of Amiloride Following Aerosolization With an Ultrasonic Nebulizer to Normal Airways

doi:10.1378/chest.112.5.1283

Chest

Volume 112, Issue 5, November 1997, Pages 1283-1290

https://doi.org/10.1378/chest.112.5.1283 Get rights and content

Study objectives

Airway epithelial ion transport is an important component of the airway defense mechanism, and new therapies that target ion transport are being developed. Amiloride is an example of such a new drug, exerting a dose-dependent action to inhibit Na⁺ transport. Amiloride may be useful in cystic fibrosis, blocking the characteristic airway epithelial Na⁺ hyperabsorption that occurs in the disease. To evaluate airway and systemic delivery of amiloride via an ultrasonic nebulizer (Omron NE-U07), we measured the airway surface concentrations of amiloride in normal volunteers via a novel approach, together with the systemic pharmacokinetics of amiloride.

Design

Direct measurement of airway surface liquid, plasma, and urine amiloride concentrations following ultrasonic nebulization.

Participants/interventions

Seven normal subjects were studied in the General Clinical Research Center of the University of North Carolina. Following inhalation with amiloride (1 mg/mL, 4.5 mL) for approximately 12 min, a bronchoscopy was performed. Amiloride deposition and clearance from airway surfaces over 1 h were evaluated by transbronchoscopic sampling using preweighed filter papers. Pulmonary and systemic absorption was assessed by measuring drug concentrations in blood and urine.

Results

The mean volume aerosolized was 3.5 ±0.3 mL during 12 min of aerosolization time; the mean initial concentration of amiloride on airway surfaces after nebulization was 1.6×10⁻⁴ mol/L, with an elimination half life of approximately 23 min. Peak plasma concentrations of amiloride (30 min, 3.36±0.70 ng/mL) suggest early absorption across lung surfaces, rather than via the GI route. Mean urinary excretion of amiloride over 72 h was 0.63±0.07 mg, with 87%; excreted in the first 24 h.

Conclusions

The ultrasonic nebulizer rapidly delivers amiloride to normal conducting airways as assessed by the transbronchoscopic sampling technique. Early blood concentrations of amiloride probably reflect initial absorption across lung surfaces and are a useful index of the efficiency of the machine.

Section snippets

Study Subjects

Eight normal subjects without any history of respiratory or allergic disease (mean age, 25.3±1.4 years; range, 22 to 33 years) were screened and included in the study (data from one subject were excluded from final analyses; see below). Subjects had normal pulmonary function test results (FEV₁=107.0±4.7%; predicted) and a normal chest radiograph. Informed consent was obtained under the auspices of the Committee on the Protection of the Rights of Human Subjects of the University of North

RESULTS

In the dry-run experiment, four HPLC chromatograms were generated from the samples collected (data not shown). The amiloride peak occurs at approximately 8 min with the same characteristics in all four chromatograms, and eluted at the same time as a known standard, thus confirming that amiloride is chemically unaltered by the process of ultrasonic nebulization. Using the nebulizer, the mass median aerodynamic diameter (MMAD) of the particles was 4.88 μm, with 54%; of the droplets in the

DISCUSSION

The past decade has seen exciting advances in our understanding of airway epithelial ion transport, an important system that contributes to mucociliary defense mechanisms.¹,² CF is a disease that is characterized by abnormalities in airway epithelial ion Na⁺ and Cl⁻ transport.²⁰ New therapies that target these abnormalities are being tested, and show promise, including amiloride and UTP.⁷,⁸,²¹ Since amiloride acts in a concentration-dependent manner to inhibit Na⁺ channels,²² evaluation of

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Amiloride, the potassium-sparing diuretic, is the most used molecular scaffold for the development of more potent ENaC blockers. Rapid clearance from the lungs and systemic side effects such as hyperkalemia drastically reduced the clinical efficacy of amiloride and derivatives as treatments for CF [18–20]. Many subsequent maneuvers including direct ENaC blockers and peptide-based inhibitors have shown promise in preclinical models but have failed to meet their primary outcome measures in clinical studies (NCT02709109, NCT02950805, NCT03229252 among others).
Disruption of the equilibrium between ion secretion and absorption processes by the airway epithelium is central to many muco-obstructive lung diseases including cystic fibrosis (CF). Besides correction of defective folding and function of CFTR, inhibition of amiloride-sensitive epithelia sodium channels (ENaC) has emerged as a bona fide therapeutic strategy to improve mucociliary clearance in patients with CF. The short half-life of amiloride-based ENaC blockers and hyperosmotic therapies have led to the development of novel RNA-based interventions for targeted and sustained reduction of ENaC expression and function in preclinical models of CF. This review summarizes the recent advances in RNA therapeutics targeting ENaC for mutation-agnostic treatment of CF.
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To better delineate the parameters influencing the systemic delivery after oral pulmonary inhalation in humans, we studied the influence of physico-chemical and permeability properties obtained in silico on the rate and extent of Fpulm in a series of 77 compounds with or without marketing approval for pulmonary delivery, and intended either for local or for systemic delivery. Principal component analysis (PCA) showed mainly that Fpulm was positively correlated with Papp and negatively correlated with %TPSA, without a significant influence of solubility and ionization fraction, and no apparent link with lipophilicity and drug size parameters.
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It can be observed that most particles deposit in either capsule or circulation chamber, while only a small percentage of particles deposit in the mouthpiece. After inhalation, amiloride enters the systemic circulation in two phases: quickly via respiratory tract, and more slowly following GI absorption of the swallowed part of the dose (Jones et al., 1997; Noone et al., 1997). Therefore, drug-specific PBPK model was first developed and validated for oral drug dosing, and further adjusted to simulate plasma profile following inhalation.
One of the critical components of the respiratory drug delivery is the manner in which the inhaled aerosol is deposited in respiratory tract compartments. Depending on formulation properties, device characteristics and breathing pattern, only a certain fraction of the dose will reach the target site in the lungs, while the rest of the drug will deposit in the inhalation device or in the mouth–throat region. The aim of this study was to link the Computational fluid dynamics (CFD) with physiologically-based pharmacokinetic (PBPK) modelling in order to predict aerolisolization of different dry powder formulations, and estimate concomitant in vivo deposition and absorption of amiloride hydrochloride. Drug physicochemical properties were experimentally determined and used as inputs for the CFD simulations of particle flow in the generated 3D geometric model of Aerolizer® dry powder inhaler (DPI). CFD simulations were used to simulate air flow through Aerolizer® inhaler and Discrete Phase Method (DPM) was used to simulate aerosol particles deposition within the fluid domain. The simulated values for the percent emitted dose were comparable to the values obtained using Andersen cascade impactor (ACI). However, CFD predictions indicated that aerosolized DPI have smaller particle size and narrower size distribution than assumed based on ACI measurements. Comparison with the literature in vivo data revealed that the constructed drug-specific PBPK model was able to capture amiloride absorption pattern following oral and inhalation administration. The PBPK simulation results, based on the CFD generated particle distribution data as input, illustrated the influence of formulation properties on the expected drug plasma concentration profiles. The model also predicted the influence of potential changes in physiological parameters on the extent of inhaled amiloride absorption. Overall, this study demonstrated the potential of the combined CFD-PBPK approach to model inhaled drug bioperformance, and suggested that CFD generated results might serve as input for the prediction of drug deposition pattern in vivo.
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The aim of this investigation was to examine the effect of a jet-mill and spray-drying process on the physicochemical and aerodynamic dispersion properties of amiloride HCl particles. Micro-fine particles were prepared by a spiral air jet-mill Hosokawa 50 AS and Mini Spray-Dryer B-191. A 2^3 -1 fractional factorial experimental design was implemented to screen three jet-mill process parameters. Possible changes in the physicochemical properties of the material due to spiral jet-milling were examined by the determination of the particle size distribution (PSD), powder true density, powder flowability, diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and scanning electron microscopy (SEM). The effect of different jet-milling parameters and the spray-drying process on the aerosol dispersion characteristics was examined with a cascade impactor with a preseparator using the Aerolizer® dry powder inhaler device (Novartis, Switzerland). The results show that small changes in the particle size within the 1 to 5 μm range had an impact on the physicochemical and aerosol dispersion properties of jet-milled and spray-dried particles.
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The effect of amiloride on the CF airway has been substantiated in vitro in respiratory epithelial cell culture [11–13] and in vivo [14] by nasal potential difference measurements across the epithelia of CF patients, where it corrects the abnormal potential difference. Nebulized amiloride has also been demonstrated in numerous trials to have an excellent safety profile [15–19], though studies of efficacy have rendered mixed results. No statistically significant effect on various outcomes including FVC, FEV1, number of hospitalizations, colonization status, and pulmonary exacerbations was demonstrated in CF patients chronically colonized with Pseudomonas aeruginosa treated with nebulized amiloride in combination with standard therapy vs. placebo (nebulized saline) control [19,20].
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Supported in part by grants from the National Institutes of Health (HL 42322, HL 42384, RR 00046), the Cystic Fibrosis Foundation (CFF L543), Omron Healthcare, Vernon Hills, Ill, the Winston Churchill Memorial Trust of Australia (J.A.R.), and Glaxo Wellcome Inc, for supporting measurements of amiloride concentrations.

Reprint requests: Peadar G. Noone, MD, FCCP, Pulmonary Division, CB #7248, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7248; email: [email protected].

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Chest

Clinical Investigations: NebulizersAirway Deposition and Clearance and Systemic Pharmacokinetics of Amiloride Following Aerosolization With an Ultrasonic Nebulizer to Normal Airways

Study objectives

Design

Participants/interventions

Results

Conclusions

Section snippets

Study Subjects

RESULTS

DISCUSSION

Chest

Respir Med

Chest

Cell

Respir Med

Respir Med

Lancet

Human airway ion transport (part 1)

Am J Respir Crit Care Med

Human airway ion transport (part 2)

Am J Respir Crit Care Med

Cystic fibrosis

Cystic fibrosis—state of the art

Am J Respir Crit Care Med

A pilot study of aerosolized amiloride for the treatment of lung disease in cystic fibrosis

N Engl J Med

Amiloride inhalation therapy in cystic fibrosis: influence on ion content, hydration, and rheology of sputum

Am Rev Respir Dis

Acute safety and effects on mucociliary clearance of aerosolized uridine 5'-triphosphate +/— amiloride in normal adults

Am J Respir Crit Care Med

Effect of uridine 5'-triphosphate plus amiloride on mucociliary clearance in adult cystic fibrosis

Am J Respir Crit Care Med

A comparison of commercial jet nebulizers

Chest

Pulmonary deposition of nebulized amiloride in cystic fibrosis: comparison of two nebulisers

Thorax

Pulmonary deposition of nebulised pentamidine isethionate: effect of nebuliser type, dose and volume of fill

Thorax

Amiloride in cystic fibrosis: safety, pharmacokinetics, and efficacy in the treatment of pulmonary disease

Extreme variability in aerosol output of the DeVilbiss 646 Jet nebulizer

Chest

Measurement of amiloride in airway surface liquid utilizing HPLC and fluorescence detection

Biomed Chromatogr

Clinical Investigations: Nebulizers
Airway Deposition and Clearance and Systemic Pharmacokinetics of Amiloride Following Aerosolization With an Ultrasonic Nebulizer to Normal Airways