Aerosol Therapy for Pneumonia in the Intensive Care Unit

Antibiotic aerosolization in patients with ventilator-associated pneumonia (VAP) allows very high concentrations of antimicrobial agents in the respiratory secretions, far more than those achievable using the intravenous route. However, data in critically ill patients with pneumonia are limited. Administration of aerosolized antibiotics might increase the likelihood of clinical resolution, but no significant improvements in important outcomes have been consistently documented. Thus, aerosolized antibiotics should be restricted to the treatment of extensively resistant gram-negative pneumonia. In these cases, the use of a vibrating-mesh nebulizer seems to be more efficient, but specific settings and conditions are required to improve lung delivery.

Inhaled Antibiotics for Gram-Negative Respiratory Infections

Gram-negative organisms comprise a large portion of the pathogens responsible for lower respiratory tract infections, especially those that are nosocomially acquired, and the rate of antibiotic resistance among these organisms continues to rise. Systemically administered antibiotics used to treat these infections often have poor penetration into the lung parenchyma and narrow therapeutic windows between efficacy and toxicity. The use of inhaled antibiotics allows for maximization of target site concentrations and optimization of pharmacokinetic/pharmacodynamic indices while minimizing systemic exposure and toxicity. This review is a comprehensive discussion of formulation and drug delivery aspects, in vitro and microbiological considerations, pharmacokinetics, and clinical outcomes with inhaled antibiotics as they apply to disease states other than cystic fibrosis. In reviewing the literature surrounding the use of inhaled antibiotics, we also highlight the complexities related to this route of administration and the shortcomings in the available evidence. The lack of novel anti-Gram-negative antibiotics in the developmental pipeline will encourage the innovative use of our existing agents, and the inhaled route is one that deserves to be further studied and adopted in the clinical arena.

Delivering antibiotics to the lungs of patients with ventilator-associated pneumonia: an update

Ventilator-associated pneumonia is a serious hospital-acquired infection, with 20-70% crude mortality and 10-40% estimated attributable mortality. Insufficient antibiotic concentrations at the infection site when these drugs are given intravenously may lead to poor outcomes, particularly when difficult-to-treat pathogens are responsible; for example, Pseudomonas aeruginosa, extended spectrum beta lactamase-producing Gram-negative bacilli, Acinetobacter spp. and/or methicillin-resistant Staphylococcus aureus. Direct drug delivery to the infection site via aerosolization combined with intravenous administration achieves concentrations exceeding MICs of the pathogens, even those with impaired susceptibility. Experimental and recent clinical results demonstrated our markedly improved ability to deliver aerosolized antibiotics to the lung with new-generation devices, for example, vibrating-mesh nebulizers. Convincing clinical data from a large randomized trial are still lacking to support the routine administration of aerosolized antibiotics to treat ventilator-associated pneumonia, even though some small-randomized trials' observations are encouraging.

Mechanisms of absorption and elimination of drugs administered by inhalation

Pulmonary drug delivery is an effective route for local or systemic drug administration. However, compared with other routes of administration, there is a scarcity of information on how drugs are absorbed from the lung. The different cell composition lining the airways and alveoli makes this task extremely complicated. Lung cell lines and primary culture cells are useful in studying the absorption mechanisms. However, it is imperative that these cell cultures express essential features required to study these mechanisms such as intact tight junctions and transporters. In vivo, the drug has to face defensive physical and immunological barriers such as mucociliary clearance and alveolar macrophages. Knowledge of the physicochemical properties of the drug and aerosol formulation is required. All of these factors interact together leading to either successful drug deposition followed by absorption or drug elimination. These aspects concerning drug transport in the lung are addressed in this review.

Prevention and management of ventilator-associated pneumonia: A survey on current practices by intensivists practicing in the Indian subcontinent

Implementation of evidence-based guidelines to prevent and manage ventilator-associated pneumonia (VAP) in the clinical setting may not be adequate. We aimed to assess the implementation of selected VAP prevention strategies, and to learn how VAP is managed by the intensivists practicing in the Indian Subcontinent. Three hundred 10-point questionnaires were distributed during an International Critical Care Conferenceheld at New Delhi in 2009. A total of 126 (42%) questionnaires distributed among delegates from India, Nepal and Sri Lanka were analyzed. Majority (96.8%) reported using VAP bundles with a high proportion including head elevation (98.4%), chlorhexidine mouthcare (83.3%), stress ulcer prophylaxis (96.8%), heat and moisture exchangers (HME, 92.9%), early weaning (94.4%), and hand washing (97.6%) as part of their VAP bundle. Use of subglottic secretion drainage (SSD, 45.2%) and closed suction systems (CSS, 74.6%) was also reported by many intensivists, whereas use of selective gut decontamination was reported by only 22.2%. Commonest method for sampling was endotracheal suction by 68.3%. Gram negative organisms were reported to be the most commonly isolated. Majority (39.7%) reported using proton pump inhibitors for stress ulcer prophylaxis and 84.1% believed that VAP contributed to increased mortality. De-escalating therapy was considered in patients responding to treatment by 57.9% and 65.9% considered adding empirical methicillin resistant Staphylococcus aureus (MRSA)coverage, while 63.5% considered adding nebulized antibiotics in certain high-risk patients. There was good concordance regarding VAP prophylaxis among the intensivists with a majority adhering to evidence-based guidelines. We could identify certain issues like the choice of agent for stress ulcer prophylaxis, use of HME filters, SSD and CSS, where there still exists some practice variability and opportunities for improvement.

Multidrug-resistant Gram-negative infections: what are the treatment options?

The emergence of multidrug-resistant (MDR) Gram-negative bacilli creates a challenge in the treatment of nosocomial infections. While the pharmaceutical pipeline is waning, two revived old antibacterials (colistin and fosfomycin), a newer one (tigecycline) and an 'improved' member of an existing class (doripenem) are the only therapeutic options left. The class of polymyxins, known since 1947 and represented mostly by polymyxin B and polymyxin E (colistin), has recently gained a principal role in the treatment of the most problematic MDR Gram-negative pathogens (such as Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae and Stenotrophomonas maltophilia). Future prospective studies are needed to answer important clinical questions, such as the possible benefit of combination with other antimicrobials versus monotherapy, the efficacy of colistin in neutropenic hosts and the role of inhaled colistin. As new pharmacokinetic data emerge, clarification of the pharmacokinetic/pharmacodynamic (PK/PD) profile of colistin as well as appropriate dosing seems urgent, while development of resistance must be carefully monitored. Fosfomycin tromethamine, a synthetic salt of fosfomycin discovered in 1969, has regained attention because of its in vitro activity against extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae and MDR P. aeruginosa. Although in use for decades in oral and parenteral formulations for a variety of infections without significant toxicity, its clinical utility in MDR infections remains to be explored in future studies. Tigecycline, the first representative of the new class of glycylcyclines, holds promise in infections from MDR K. pneumoniae (K. pneumoniae carbapenemase [KPC]- and ESBL-producing strains) and Enterobacteriaceae with various mechanisms of resistance. The in vitro activity of tigecycline against A. baumannii makes it a tempting option, as it is currently the most active compound against MDR strains along with colistin. However, the usual minimum inhibitory concentration values of this pathogen are approximately 2 mg/L and compromise clinical outcomes based on PK/PD issues. Its advantageous penetration into various tissues is useful in infections of the skin and soft tissues as well as intra-abdominal infections (official indications), whereas low serum concentrations compromise its use in bloodstream infections. Therefore, prospective studies with dose escalation are urgently needed, as well as clarification of its role in nosocomial pneumonia, after poor results in the study of ventilator-associated pneumonia. Finally, doripenem, the recently licensed member of the carbapenems (without significant spectrum alterations from the ascendant members) seems to possess a lower potential for resistance selection and a more favourable pharmacokinetic profile when given as an extended infusion. The latter strategy could prove helpful in overcoming low level resistance of A. baumannii and P. aeruginosa strains.

Inhaled therapeutics for prevention and treatment of pneumonia

The lungs are the most common site of serious infection owing to their large surface area exposed to the external environment and minimum barrier defense. However, this architecture makes the lungs readily available for topical therapy. Therapeutic aerosols include those directed towards improving mucociliary clearance of pathogens, stimulation of innate resistance to microbial infection, cytokine stimulation of immune function and delivery of antibiotics. In our opinion inhaled antimicrobials are underused, especially in patients with difficult-to-treat lung infections. The use of inhaled antimicrobial therapy has become an important part of the treatment of airway infection with Pseudomonas aeruginosa in cystic fibrosis and the prevention of invasive fungal infection in patients undergoing heart and lung transplantation. Cytokine inhaled therapy has also been explored in the treatment of neoplastic and infectious disease. The choice of pulmonary drug delivery systems remains critical as air-jet and ultrasonic nebulizer may deliver sub-optimum drug concentration if not used properly. In future development of this field, we recommend an emphasis on the study of the use of aerosolized hypertonic saline solution to reduce pathogen burden in the airways of subjects infected with microbes of low virulence, stimulation of innate resistance to prevent pneumonia in immunocompromised subjects using cytokines or synthetic pathogen-associated molecular pattern analogues and more opportunities for the use of inhaled antimicrobials. These therapeutics are still in their infancy but show great promise.

Inhalational therapies for the ICU

PURPOSE OF REVIEW

Although drug therapy is most commonly delivered via the intravenous route, novel inhaled agents have been introduced for use in the ICU. Additionally, drugs previously delivered intravenously are now being delivered via the respiratory tract in an effort to reduce systemic toxicity and maximize effectiveness.

RECENT FINDINGS

Aerosolized antibiotics have seen increased use in an effort to reduce systemic effects, reduce ventilator-associated pneumonia, and direct high drug concentrations at the site of infection. Drug-resistant pneumonia has also been effectively treated with aerosolized antibiotics. Secretion management includes a host of devices, therapies, and drugs, but the evidence for these is scant. Cardiac drugs via the endotracheal route should be used only when intravenous access is delayed. Inhaled nitric oxide has a defined role in care of infants, although new indications have limited and conflicting data. The use of helium-oxygen mixtures provides symptom relief in a wide variety of scenarios associated with turbulent flow in large airways.

SUMMARY

Inhaled nitric oxide has an established role in neonatal intensive care and a limited role in adult intensive care. Heliox provides symptom relief, but at present cannot be considered routine as a consequence of the multiple technological challenges. Inhaled antimicrobials appear to provide a therapeutic advantage in select individuals with pneumonia. Secretion management is best achieved by adequate humidification and as needed suctioning. The role of inhaled carbon monoxide in critical care holds significant promise, but is currently in early clinical trials.

Aerosolized antibiotics to treat ventilator-associated pneumonia

PURPOSE OF REVIEW

This review summarizes the recent data on antibiotic aerosolization to treat ventilator-associated pneumonia.

RECENT FINDINGS

Most studies on antibiotic aerosolization have been case reports or descriptive studies. The results of a recent randomized, placebo-controlled trial indicated that adjunctive use of nebulized antibiotic with intravenous antibiotics to treat purulent tracheobronchitis was associated with a better outcome than placebo aerosolization. A randomized study, so far published only as an abstract, showed that amikacin aerosolized with a vibrating-mesh nebulizer--a new-generation device--was well distributed in the lung parenchyma and might lead to less intravenous antibiotic use. Several thorough reviews on nebulization devices, techniques and drawbacks have been published recently.

SUMMARY

Despite recent promising findings, the widespread use of aerosolized antibiotics to treat ventilator-associated pneumonia cannot be recommended. It should be restricted to the treatment of multidrug-resistant Gram-negative ventilator-associated pneumonia.