Optimal airway antimicrobial therapy for cystic fibrosis: the role of inhaled aztreonam lysine

Inhaled Medicines: Past, Present, and Future

The purpose of this review is to summarize essential pharmacological, pharmaceutical, and clinical aspects in the field of orally inhaled therapies that may help scientists seeking to develop new products. After general comments on the rationale for inhaled therapies for respiratory disease, the focus is on products approved approximately over the last half a century. The organization of these sections reflects the key pharmacological categories. Products for asthma and chronic obstructive pulmonary disease include β -2 receptor agonists, muscarinic acetylcholine receptor antagonists, glucocorticosteroids, and cromones as well as their combinations. The antiviral and antibacterial inhaled products to treat respiratory tract infections are then presented. Two "mucoactive" products-dornase α and mannitol, which are both approved for patients with cystic fibrosis-are reviewed. These are followed by sections on inhaled prostacyclins for pulmonary arterial hypertension and the challenging field of aerosol surfactant inhalation delivery, especially for prematurely born infants on ventilation support. The approved products for systemic delivery via the lungs for diseases of the central nervous system and insulin for diabetes are also discussed. New technologies for drug delivery by inhalation are analyzed, with the emphasis on those that would likely yield significant improvements over the technologies in current use or would expand the range of drugs and diseases treatable by this route of administration. SIGNIFICANCE STATEMENT: This review of the key aspects of approved orally inhaled drug products for a variety of respiratory diseases and for systemic administration should be helpful in making judicious decisions about the development of new or improved inhaled drugs. These aspects include the choices of the active ingredients, formulations, delivery systems suitable for the target patient populations, and, to some extent, meaningful safety and efficacy endpoints in clinical trials.

Genomic Analysis Identifies Novel Pseudomonas aeruginosa Resistance Genes under Selection during Inhaled Aztreonam Therapy In Vivo

Inhaled aztreonam is increasingly used for chronic Pseudomonas aeruginosa suppression in patients with cystic fibrosis (CF), but the potential for that organism to evolve aztreonam resistance remains incompletely explored. Here, we performed genomic analysis of clonally related pre- and posttreatment CF clinical isolate pairs to identify genes that are under positive selection during aztreonam therapy in vivo We identified 16 frequently mutated genes associated with aztreonam resistance, the most prevalent being ftsI and ampC, and 13 of which increased aztreonam resistance when introduced as single gene transposon mutants. Several previously implicated aztreonam resistance genes were found to be under positive selection in clinical isolates even in the absence of inhaled aztreonam exposure, indicating that other selective pressures in the cystic fibrosis airway can promote aztreonam resistance. Given its potential to confer plasmid-mediated resistance, we further characterized mutant ampC alleles and performed artificial evolution of ampC for maximal activity against aztreonam. We found that naturally occurring ampC mutants conferred variably increased resistance to aztreonam (2- to 64-fold) and other β-lactam agents but that its maximal evolutionary capacity for hydrolyzing aztreonam was considerably higher (512- to 1,024-fold increases) and was achieved while maintaining or increasing resistance to other drugs. These studies implicate novel chromosomal aztreonam resistance determinants while highlighting that different mutations are favored during selection in vivo and in vitro, show that ampC has a high maximal potential to hydrolyze aztreonam, and provide an approach to disambiguate mutations promoting specific resistance phenotypes from those more generally increasing bacterial fitness in vivo.

Antimicrobial molecules in the lung: formulation challenges and future directions for innovation

Inhaled antimicrobials have been extremely beneficial in treating respiratory infections, particularly chronic infections in a lung with cystic fibrosis. The pulmonary delivery of antibiotics has been demonstrated to improve treatment efficacy, reduce systemic side effects and, critically, reduce drug exposure to commensal bacteria compared with systemic administration, reducing selective pressure for antimicrobial resistance. This review will explore the specific challenges of pulmonary delivery of a number of differing antimicrobial molecules, and the formulation and technological approaches that have been used to overcome these difficulties. It will also explore the future challenges being faced in the development of inhaled products and respiratory infection treatment, and identify future directions of innovation, with a particular focus on respiratory infections caused by multiple drug-resistant pathogens.

Cystic Fibrosis Airway Microbiome: Overturning the Old, Opening the Way for the New

The genetic disease cystic fibrosis (CF) is associated with chronic airway infections that are a proximal cause of death in many patients with this affliction. Classic microbiology studies focusing on canonical pathogens resulted in the development of a common set of views regarding the nature of the airway infections associated with this disease, and these ideas have influenced everything from the way infections are treated to how clinical trials for new CF-targeted antibiotics are designed and the focus of CF-related research topics. Recent culture-independent studies have prompted us to rethink, and in some cases discard, some of these long-held views. In this piece, I argue that an updated view of the complicated chronic infections associated with CF, thanks in large part to culture-independent studies of sputum and bronchoalveolar lavage fluid samples, should be leveraged to develop new strategies to treat these recalcitrant infections.

Patient-specific modeling of regional antibiotic concentration levels in airways of patients with cystic fibrosis: are we dosing high enough?

Background

Pseudomonas aeruginosa (Pa) infection is an important contributor to the progression of cystic fibrosis (CF) lung disease. The cornerstone treatment for Pa infection is the use of inhaled antibiotics. However, there is substantial lung disease heterogeneity within and between patients that likely impacts deposition patterns of inhaled antibiotics. Therefore, this may result in airways below the minimal inhibitory concentration of the inhaled agent. Very little is known about antibiotic concentrations in small airways, in particular the effect of structural lung abnormalities. We therefore aimed to develop a patient-specific airway model to predict concentrations of inhaled antibiotics and to study the impact of structural lung changes and breathing profile on local concentrations in airways of patients with CF.

Methods

In- and expiratory CT-scans of children with CF (5–17 years) were scored (CF-CT score), segmented and reconstructed into 3D airway models. Computational fluid dynamic (CFD) simulations were performed on 40 airway models to predict local Aztreonam lysine for inhalation (AZLI) concentrations. Patient-specific lobar flow distribution and nebulization of 75 mg AZLI through a digital Pari eFlow model with mass median aerodynamic diameter range were used at the inlet of the airway model. AZLI concentrations for central and small airways were computed for different breathing patterns and airway surface liquid thicknesses.

Results

In most simulated conditions, concentrations in both central and small airways were well above the minimal inhibitory concentration. However, small airways in more diseased lobes were likely to receive suboptimal AZLI. Structural lung disease and increased tidal volumes, respiratory rates and larger particle sizes greatly reduced small airway concentrations.

Conclusions

CFD modeling showed that concentrations of inhaled antibiotic delivered to the small airways are highly patient specific and vary throughout the bronchial tree. These results suggest that anti-Pa treatment of especially the small airways can be improved.

Pharmacokinetics and pharmacodynamics of aerosolized antibacterial agents in chronically infected cystic fibrosis patients

Bacteria adapt to growth in lungs of patients with cystic fibrosis (CF) by selection of heterogeneously resistant variants that are not detected by conventional susceptibility testing but are selected for rapidly during antibacterial treatment. Therefore, total bacterial counts and antibiotic susceptibilities are misleading indicators of infection and are not helpful as guides for therapy decisions or efficacy endpoints. High drug concentrations delivered by aerosol may maximize efficacy, as decreased drug susceptibilities of the pathogens are compensated for by high target site concentrations. However, reductions of the bacterial load in sputum and improvements in lung function were within the same ranges following aerosolized and conventional therapies. Furthermore, the use of conventional pharmacokinetic/pharmacodynamic (PK/PD) surrogates correlating pharmacokinetics in serum with clinical cure and presumed or proven eradication of the pathogen as a basis for PK/PD investigations in CF patients is irrelevant, as minimization of systemic exposure is one of the main objectives of aerosolized therapy; in addition, bacterial pathogens cannot be eradicated, and chronic infection cannot be cured. Consequently, conventional PK/PD surrogates are not applicable to CF patients. It is nonetheless obvious that systemic exposure of patients, with all its sequelae, is minimized and that the burden of oral treatment for CF patients suffering from chronic infections is reduced.

In vitro evaluation of tobramycin and aztreonam versus Pseudomonas aeruginosa biofilms on cystic fibrosis-derived human airway epithelial cells

OBJECTIVES

Aztreonam for inhalation solution (AZLI) was recently approved by the FDA for treating cystic fibrosis (CF) patients infected with Pseudomonas aeruginosa. Here we investigated the effect of aztreonam alone or in combination with tobramycin on P. aeruginosa biofilms grown on CF airway epithelial cells.

METHODS

P. aeruginosa biofilms, produced by laboratory strains or clinical isolates, were formed on confluent CF airway cells before treatment overnight with aztreonam or tobramycin alone or in combination. Alternatively, antibiotics were added 1 h after bacterial inoculation to assess their ability to impair biofilm formation at 5 h. Bacterial cfu remaining after treatment were then determined by plate counting.

RESULTS

In the absence of antibiotics, all strains developed biofilms that disrupted CF airway epithelial monolayers overnight. Tobramycin reduced the cfu of all strains grown as biofilms. Aztreonam reduced the cfu of some strains by ∼1 log unit without preserving the integrity of cystic fibrosis airway cell monolayers, while decreasing the biofilms of other clinical isolates by ∼4 log units and protecting the monolayers from being compromised. The combination of aztreonam and tobramycin reduced the cfu of two strains by an additional 0.5 and 2 log units, respectively. Of all the mechanisms explored, Psl exopolysaccharide production might explain the variations in biofilm tolerance to aztreonam in some of the strains.

CONCLUSIONS

Effects of aztreonam on P. aeruginosa biofilms in the in vitro co-culture model are strain-dependent. The simultaneous application of aztreonam and tobramycin may be beneficial for a subset of CF patients by eliminating susceptible P. aeruginosa strains.

Aztreonam lysine for inhalation: new formulation of an old antibiotic

PURPOSE

The pharmacology, safety, efficacy, pharmacokinetics, pharmacodynamics, current place in therapy, and potential future therapeutic uses of inhaled aztreonam are reviewed.

SUMMARY

Inhaled aztreonam, a newly formulated lysine salt of the original monobactam antibiotic, is approved for the treatment of respiratory symptoms in patients with cystic fibrosis (CF) who are colonized with Pseudomonas aeruginosa. Its spectrum of activity is limited to susceptible gram-negative organisms, including P. aeruginosa. Lyophilized aztreonam lysine is diluted with 0.17% sodium chloride and administered using the Altera nebulizer system, which produces appropriate-sized particles for proper deposition in the lungs to achieve high sputum and low systemic concentrations. Mean sputum drug concentrations are highest 10 minutes after dose administration, and plasma concentrations peak one hour after inhalation. Aztreonam is excreted via active tubular secretion and glomerular filtration. Caution is advised in patients with renal or hepatic impairment, breastfeeding women, and patients age 65 years or older. Like the older i.v. formulation, inhaled aztreonam displays time-dependent killing. Phase III clinical trials have shown improvements in respiratory symptoms, decreased P. aeruginosa sputum density, prolonged time intervals between antibiotic treatments, and efficacy without the development of resistance in the face of repeated exposures. This formulation is available only from select specialty pharmacies and should only be used with the Altera nebulizer system.

CONCLUSION

Inhaled aztreonam has shown efficacy and safety in patients seven years of age or older with CF who have P. aeruginosa airway infections. This product may complement existing therapies and offers the advantage of a new inhaled formulation to aid in treatment regimens.

Inhaled antibiotics for Gram-negative respiratory infections

Several disease states create conditions that lead to opportunistic Gram-negative respiratory infections. Inhalation is the most direct and, until recently, underutilized means of antimicrobial drug targeting for respiratory tract infections. All approved antimicrobial agents for administration by inhalation are indicated for Pseudomonas aeruginosa infections in patients with cystic fibrosis. These inhaled therapies have directly contributed to a significant reduction in exacerbations and hospitalizations in this patient population over the last few decades. The relentless adaptation of pathogenic organisms to current treatment options demands that the pharmaceutical industry continue designing next-generation antimicrobial agents over 70 years after they were first introduced. Recent technological advances in inhalation devices and drug formulation techniques have broadened the scope of antimicrobial structural classes that can be investigated by inhalation; however, there is an urgent need to discover novel compounds with improved resistance profiles relative to those drugs that are already marketed.

Outpatient treatment of Pseudomonas aeruginosa bronchial colonization with long-term inhaled colistin, tobramycin, or both in adults without cystic fibrosis

STUDY OBJECTIVE

To compare clinical and microbiologic outcomes in adults without cystic fibrosis who had Pseudomonas aeruginosa bronchial colonization and were receiving inhaled colistin or colistin plus tobramycin with those who were receiving inhaled tobramycin as outpatient treatment.

DESIGN

Prospective, observational cohort study.

SETTING

Referral pneumology service at a tertiary university care hospital.

PATIENTS

Eighty-one Caucasian adults without cystic fibrosis who received 97 courses of inhaled colistin alone, colistin plus tobramycin, or inhaled tobramycin alone as outpatient treatment of P. aeruginosa bronchial colonization between January 2004 and December 2008.

MEASUREMENTS AND MAIN RESULTS

The frequency and duration of hospitalizations for respiratory exacerbations were the primary outcomes compared among treatment groups. Secondary outcomes were emergence of bacterial resistance, antibiotic use during admission, emergence of other opportunistic microorganisms, achievement of sustained P. aeruginosa eradication in the airways, and mortality, as well as safety and changes in respiratory function. No significant differences between colistin and tobramycin were found in the mean number of hospital admissions, duration of hospitalizations, duration of antibiotic treatment, adverse events, mortality, or emergence of other opportunistic microorganisms. Emergence of resistance to colistin was lower than resistance to tobramycin (hazard ratio 0.09, 95% confidence interval [CI] 0.03-0.32). Patients treated with both inhaled antibiotics had fewer days of hospitalization and fewer days of antibiotic use than those treated with tobramycin alone (relative risk [RR] 0.33, 95% CI 0.10-1.12, and RR 0.27, 95% CI 0.08-0.93, respectively).

CONCLUSION

Results with colistin were similar to those with tobramycin for inhaled treatment of P. aeruginosa colonization in this population; however, combined use of colistin and tobramycin appeared to be associated with fewer days of hospitalization and shorter duration of antibiotic treatment. Prospective, double-blind, placebo-controlled trials of outpatient nebulized antibiotics, especially colistin plus tobramycin, should be performed to ascertain the efficacy of this therapy for treatment of P. aeruginosa colonization in patients without cystic fibrosis.