Role of nebulized antibiotics for the treatment of respiratory infections

New Broth Macrodilution Volatilization Method for Antibacterial Susceptibility Testing of Volatile Agents and Evaluation of Their Toxicity Using Modified MTT Assay In Vitro

In this study, a new broth macrodilution volatilization method for the simple and rapid determination of the antibacterial effect of volatile agents simultaneously in the liquid and vapor phase was designed with the aim to assess their therapeutic potential for the development of new inhalation preparations. The antibacterial activity of plant volatiles (β-thujaplicin, thymohydroquinone, thymoquinone) was evaluated against bacteria associated with respiratory infections (Haemophilus influenzae, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes) and their cytotoxicity was determined using a modified thiazolyl blue tetrazolium bromide assay against normal lung fibroblasts. Thymohydroquinone and thymoquinone possessed the highest antibacterial activity against H. influenzae, with minimum inhibitory concentrations of 4 and 8 µg/mL in the liquid and vapor phases, respectively. Although all compounds exhibited cytotoxic effects on lung cells, therapeutic indices (TIs) suggested their potential use in the treatment of respiratory infections, which was especially evident for thymohydroquinone (TI > 34.13). The results demonstrate the applicability of the broth macrodilution volatilization assay, which combines the principles of broth microdilution volatilization and standard broth macrodilution methods. This assay enables rapid, simple, cost- and labor-effective screening of volatile compounds and overcomes the limitations of assays currently used for screening of antimicrobial activity in the vapor phase.

Colistin inhalation monotherapy for ventilator-associated pneumonia of Acinetobacter baumannii in prematurity

BACKGROUND

Ventilator-associated pneumonia (VAP) caused by Acinetobacter baumannii is increasing. It has a high mortality rate but experience in using inhaled colistin as monotherapy for VAP in children, especially pre-term infants, is limited. This study presents experiences using aerosolized colistin as monotherapy for VAP due to A. baumannii infection in pre-term infants.

METHODS

Eight pre-term infants (gestational age 25-36 weeks) admitted to the neonatal intensive care unit (NICU) of Kaohsiung Chang Gung Memorial Hospital in Taiwan from January 2006 to December 2010 who received inhaled colistin as monotherapy for VAP due to A. baumannii infection were retrospectively evaluated. Of the isolated microorganisms, five were multi-drug resistant strains of A. baumannii (MDR-AB) but all were sensitive to colistin. All patients received inhaled colistin at a dose of 1,000,000 IU (33.4 mg) twice daily for an average of 9.1 days (range, 4-22 days).

RESULTS

All pre-term infants were cured, with A. baumannii eradicated from airway secretions. There were no clinical or laboratory adverse events related to colistin use.

CONCLUSIONS

Aerosolized colistin may be used as monotherapy for VAP due to A. baumannii infection in pre-term infants. A larger controlled study is warranted to corroborate the findings.

Role of inhaled antibacterials in hospital-acquired and ventilator-associated pneumonia

Inhaled antibiotics are not usually considered outside the setting of cystic fibrosis or Pneumocystis jiroveci prophylaxis. However, because they deliver high drug concentrations at the site of infection with negligible systemic absorption and toxicity, they are logical compliments to standard intravenous therapy for severe nosocomial pneumonias -- particularly those caused by multiresistant organisms. Older studies that have shown marginal or no benefit have either applied inhaled antibiotics indiscriminately to low risk populations, or have used crude delivery systems, such as hand atomizers or poured it into the endotracheal tube. Although inhaled antibiotics cannot be recommended for prevention of nosocomial pneumonia at this time, a few studies involving prophylaxis have shown promising trends, particularly in high-risk patients with predisposing conditions. The greatest potential of inhaled antibiotics lies in the treatment of severe healthcare-associated pneumonia caused by a multiresistant organism. The method of delivery is extremely important. Trials that have shown the most benefit, even against pathogens most difficult to eradicate and in damaged lungs, have used optimized delivery systems. Most authorities recommend using ultrasonic or vibrating disk nebulizers to generate particle sizes between 1 and 5 microm that are crucial for deposition in terminal bronchioles and alveoli. Inhaled liposomal amphotericin has also demonstrated encouraging results in animal trials. Recently, inhaled phytochemicals were successfully employed in the treatment of a patient with primary pulmonary tuberculosis. When used selectively in high-risk patients, or in the treatment of established pneumonia, inhaled antibiotics have not been associated with development of resistant organisms.

Elevated tobramycin concentrations following endotracheal administration in a premature infant

The following case report describes a 1-month-old, 34-week-gestation premature neonate who had compromised renal function. The neonate received endotracheally administered tobramycin (300 mg every 12 hours) via a PARI PLUS reusable nebulizer to treat a documented Gram-negative tracheostomy infection. The patient also received systemic tobramycin (2.5 mg/kg intravenously every 18 hours). The tobramycin serum concentration obtained 45 hours after the last intravenous dose and 11.5 hours after the second nebulized dose was 17.6 mg/L. The tobramycin nebulizations were stopped.

Inhaled antibiotic therapy for ventilator-associated tracheobronchitis and ventilator-associated pneumonia: an update

Ventilator-associated pneumonia (VAP) remains a leading cause of morbidity and mortality in mechanically-ventilated patients in the Intensive Care Unit (ICU). Ventilator-associated tracheobronchitis (VAT) was previously believed to be an intermediate stage between colonization of the lower respiratory tract and VAP. More recent data, however, suggest that VAT may be a separate entity that increases morbidity and mortality, independently of the occurrence of VAP. Some, but not all, patients with VAT progress to develop VAP. Although inhaled antibiotics alone could be effective for the treatment of VAP, the current consensus of opinion favors their role as adjuncts to systemic antimicrobial therapy for VAP. Inhaled antibiotics are increasingly employed for salvage therapy in patients with VAP due to multi-drug resistant Gram-negative bacteria. In contrast to VAP, VAT could be effectively treated with inhaled antibiotic therapy alone or in combination with systemic antimicrobials.

Pharmacokinetics and lung delivery of PDDS-aerosolized amikacin (NKTR-061) in intubated and mechanically ventilated patients with nosocomial pneumonia

Introduction

Aminoglycosides aerosolization might achieve better diffusion into the alveolar compartment than intravenous use. The objective of this multicenter study was to evaluate aerosol-delivered amikacin penetration into the alveolar epithelial lining fluid (ELF) using a new vibrating mesh nebulizer (Pulmonary Drug Delivery System (PDDS), Nektar Therapeutics), which delivers high doses to the lungs.

Methods

Nebulized amikacin (400 mg bid) was delivered to the lungs of 28 mechanically ventilated patients with Gram-negative VAP for 7-14 days, adjunctive to intravenous therapy. On treatment day 3, 30 minutes after completing aerosol delivery, all the patients underwent bronchoalveolar lavage in the infection-involved area and the ELF amikacin concentration was determined. The same day, urine and serum amikacin concentrations were determined at different time points.

Results

Median (range) ELF amikacin and maximum serum amikacin concentrations were 976.1 (135.7-16127.6) and 0.9 (0.62-1.73) μg/mL, respectively. The median total amount of amikacin excreted in urine during the first and second 12-hour collection on day 3 were 19 (12.21-28) and 21.2 (14.1-29.98) μg, respectively. During the study period, daily through amikacin measurements were below the level of nephrotoxicity. Sixty-four unexpected adverse events were reported, among which 2 were deemed possibly due to nebulized amikacin: one episode of worsening renal failure, and one episode of bronchospasm.

Conclusions

PDDS delivery of aerosolized amikacin achieved very high aminoglycoside concentrations in ELF from radiography-controlled infection-involved zones, while maintaining safe serum amikacin concentrations. The ELF concentrations always exceeded the amikacin minimum inhibitory concentrations for Gram-negative microorganisms usually responsible for these pneumonias. The clinical impact of amikacin delivery with this system remains to be determined.

Trial Registration

ClinicalTrials.gov Identifier: NCT01021436.

Pulmonary versus systemic delivery of antibiotics: comparison of vancomycin dispositions in the isolated rat lung

Vancomycin dispositions in the respiratory system were compared after systemic and inhalatory administration under two respiratory conditions using the isolated-lung model. Inhalatory delivery led to much higher drug levels in pulmonary tissue and fluids. The respiratory pattern affects vancomycin disposition in the pulmonary system regardless of the administration route.

Pseudomonas aeruginosa: resistance and therapeutic options at the turn of the new millennium

Pseudomonas aeruginosa is a major cause of nosocomial infections. This organism shows a remarkable capacity to resist antibiotics, either intrinsically (because of constitutive expression of beta-lactamases and efflux pumps, combined with low permeability of the outer-membrane) or following acquisition of resistance genes (e.g., genes for beta-lactamases, or enzymes inactivating aminoglycosides or modifying their target), over-expression of efflux pumps, decreased expression of porins, or mutations in quinolone targets. Worryingly, these mechanisms are often present simultaneously, thereby conferring multiresistant phenotypes. Susceptibility testing is therefore crucial in clinical practice. Empirical treatment usually involves combination therapy, selected on the basis of known local epidemiology (usually a beta-lactam plus an aminoglycoside or a fluoroquinolone). However, therapy should be simplified as soon as possible, based on susceptibility data and the patient's clinical evolution. Alternative drugs (e.g., colistin) have proven useful against multiresistant strains, but innovative therapeutic options for the future remain scarce, while attempts to develop vaccines have been unsuccessful to date. Among broad-spectrum antibiotics in development, ceftobiprole, sitafloxacin and doripenem show interesting in-vitro activity, although the first two molecules have been evaluated in clinics only against Gram-positive organisms. Doripenem has received a fast track designation from the US Food and Drug Administration for the treatment of nosocomial pneumonia. Pump inhibitors are undergoing phase I trials in cystic fibrosis patients. Therefore, selecting appropriate antibiotics and optimising their use on the basis of pharmacodynamic concepts currently remains the best way of coping with pseudomonal infections.

Targeting mechanisms of Pseudomonas aeruginosa pathogenesis

Pseudomonas aeruginosa is an opportunistic pathogen responsible for ventilator-acquired pneumonia, acute lower respiratory tract infections in immunocompromised patients and chronic respiratory infections in cystic fibrosis patients. High incidence, infection severity and increasing resistance characterize P. aeruginosa infections, highlighting the need for new therapeutic options. One such option is to target the many pathogenic mechanisms conferred to P. aeruginosa by its large genome encoding many different virulence factors. This article reviews the pathogenic mechanisms and potential therapies targeting these mechanisms in P. aeruginosa respiratory infections.