Aerosolized Antibiotics in the Treatment of Ventilator Associated Pneumonia: A Pilot Study

Ventilator associated pneumonia (VAP) remains a serious problem in critically ill patients with an incidence of 8-28% and mortality ranging from 24-57%. A landmark study comparing eight days versus fifteen days of antibiotic therapy reported a pulmonary infection recurrence rate of 26-29%. Costs associated with VAP can reach up to $40,000 per occurrence.

Aerosolized antibiotics have been used to treat ailments such as cystic fibrosis and bronchiectasis. Previous research indicates that aerosolized antibiotics attain a 200 fold greater concentration in the lung than in the blood, and that sputum trough levels remain 20 fold greater than that of acceptable serum antibiotic troughs. Additionally, aerosolized antibiotics are considered safe (without increased risk of bacterial resistance) with better treatment success when compared to controls (OR 2.75, 95% CI 1.06-7.17), although no mortality benefit has been identified. Some studies have shown reduced systemic toxicity when using aerosolized antibiotics while others have shown no difference. Aerosolized tobramycin prevents pseudomonas infections in patients with Cystic Fibrosis. Furthermore aerosolized antibiotics improve pulmonary function in these patients, including Forced Expiratory Volume in 1 second (FEV1), and decrease the need for hospitalization. Lung transplant patients and patients with Human Immunodeficiency Virus (HIV) also benefit from aerosolized fungal prophylaxis and treatment. The benefit has been less clear in patients with non-Cystic Fibrosis bronchiectasis, and although some studies show benefits to aerosolized antibiotics in preventing and treating nosocomial pneumonias, no large prospective randomized trials have been performed to confirm the benefit or to change practice recommendations.

Antimicrobials must reach the site of infection, bind the target site, and remain bound for a sufficient time period to disrupt the life cycle of the cells. Only 21% of an administered antibiotic dose actually ends up in the lung parenchyma. Multiple studies have shown that the ideal particle size for inhalation is between 1 and 5 microns. Particles that are too small get exhaled, and particles that are too large do not reach the alveoli. Non-humidified nebulization is better for drug administration than humidified air. Isotonicity of the drug, pH, and the presence of preservatives in the solution also need to be evaluated for optimal drug delivery and function. The ideal method of administration of aerosolized antibiotics also remains to be determined.

Inhaled tobramycin has been used in several studies over the past thirty years, mostly in patients with Cystic Fibrosis. It has been shown to be effective in decreasing sputum colony counts of Pseudomonas Aeruginosa. Inhaled gentamycin has also been shown to delay acquisition of Pseudomonas in children with Cystic Fibrosis, as well as decreasing disease progression. Chest tightness and persistent cough are the side effects mentioned within these studies. This suggests that inhalation is a safe method for the administration of tobramycin.

It has been shown that in Community-Acquired Pneumonia (CAP) the alveolar macrophages initiate a pro-inflammatory cascade. Failure to control excessive inflammation, leads to an exaggerated systemic response resulting in organ damage. Local and systemic levels of these pro-inflammatory mediators have been shown to correlate with the severity of disease. The investigators speculate that a similar response exists in patients with VAP.