Inhaled amikacin for pneumonia treatment and dissemination prevention: an experimental model of severe monolateral Pseudomonas aeruginosa pneumonia.

BACKGROUND: Pseudomonas aeruginosa pneumonia is commonly treated with systemic antibiotics to ensure adequate treatment of multidrug resistant (MDR) bacteria. However, intravenous (IV) antibiotics often achieve suboptimal pulmonary concentrations. We therefore aimed to evaluate the effect of inhaled amikacin (AMK) plus IV meropenem (MEM) on bactericidal efficacy in a swine model of monolateral MDR P. aeruginosa pneumonia. METHODS: We ventilated 18 pigs with monolateral MDR P. aeruginosa pneumonia for up to 102 h. At 24 h after the bacterial challenge, the animals were randomized to receive 72 h of treatment with either inhaled saline (control), IV MEM only, or IV-MEM plus inhaled AMK (MEM + AMK). We dosed IV MEM at 25 mg/kg every 8 h and inhaled AMK at 400 mg every 12 h. The primary outcomes were the P. aeruginosa burden and histopathological injury in lung tissue. Secondary outcomes included the P. aeruginosa burden in tracheal secretions and bronchoalveolar lavage fluid, the development of antibiotic resistance, the antibiotic distribution, and the levels of inflammatory markers. RESULTS: The median (25-75th percentile) P. aeruginosa lung burden for animals in the control, MEM only, and MEM + AMK groups was 2.91 (1.75-5.69), 0.72 (0.12-3.35), and 0.90 (0-4.55) log10 CFU/g (p = 0.009). Inhaled therapy had no effect on preventing dissemination compared to systemic monotherapy, but it did have significantly higher bactericidal efficacy in tracheal secretions only. Remarkably, the minimum inhibitory concentration of MEM increased to > 32 mg/L after 72-h exposure to monotherapy in 83% of animals, while the addition of AMK prevented this increase (p = 0.037). Adjunctive therapy also slightly affected interleukin-1ß downregulation. Despite finding high AMK concentrations in pulmonary samples, we found no paired differences in the epithelial lining fluid concentration between infected and non-infected lungs. Finally, a non-significant trend was observed for higher amikacin penetration in low-affected lung areas. CONCLUSIONS: In a swine model of monolateral MDR P. aeruginosa pneumonia, resistant to the inhaled AMK and susceptible to the IV antibiotic, the use of AMK as an adjuvant treatment offered no benefits for either the colonization of pulmonary tissue or the prevention of pathogen dissemination. However, inhaled AMK improved bacterial eradication in the proximal airways and hindered antibiotic resistance.

Development and characterization of a new swine model of invasive pneumococcal pneumonia.

Streptococcus pneumoniae is the most common microbial cause of community-acquired pneumonia. Currently, there are no available models of severe pneumococcal pneumonia in mechanically ventilated animals to mimic clinical conditions of critically ill patients. We studied endogenous pulmonary flora in 4 healthy pigs and in an additional 10 pigs in which we intra-bronchially instilled S. pneumoniae serotype 19 A, characterized by its resistance to penicillin, macrolides and tetracyclines. The pigs underwent ventilation for 72 h. All pigs that were not challenged with S. pneumoniae completed the 72-h study, whereas 30% of infected pigs did not. At 24 h, we clinically confirmed pneumonia in the infected pigs; upon necropsy, we sampled lung tissue for microbiological/histological confirmation of pneumococcal pneumonia. In control pigs, Streptococcus suis and Staphylococcus aureus were the most commonly encountered pathogens, and their lung tissue mean ± s.e.m. concentration was 7.94 ± 20 c.f.u./g. In infected pigs, S. pneumoniae was found in the lungs of all pigs (mean ± s.e.m. pulmonary concentration of 1.26 × 105 ± 2 × 102 c.f.u./g). Bacteremia was found in 50% of infected pigs. Pneumococcal pneumonia was confirmed in all infected pigs at 24 h. Pneumonia was associated with thrombocytopenia, an increase in prothrombin time, cardiac output and vasopressor dependency index and a decrease in systemic vascular resistance. Upon necropsy, microbiological/histological pneumococcal pneumonia was confirmed in 8 of 10 pigs. We have therefore developed a novel model of penicillin- and macrolide-resistant pneumococcal pneumonia in mechanically ventilated pigs with bacteremia and severe hemodynamic compromise. The model could prove valuable for appraising the pathogenesis of pneumococcal pneumonia, the effects associated with macrolide resistance and the outcomes related to the use of new diagnostic strategies and antibiotic or complementary therapies.

Short-Term Effects of Appropriate Empirical Antimicrobial Treatment with Ceftolozane/Tazobactam in a Swine Model of Nosocomial Pneumonia.

The rising frequency of multidrug-resistant and extensively drug-resistant (MDR/XDR) pathogens is making more frequent the inappropriate empirical antimicrobial therapy (IEAT) in nosocomial pneumonia, which is associated with increased mortality. We aim to determine the short-term benefits of appropriate empirical antimicrobial treatment (AEAT) with ceftolozane/tazobactam (C/T) compared with IEAT with piperacillin/tazobactam (TZP) in MDR Pseudomonas aeruginosa pneumonia. Twenty-one pigs with pneumonia caused by an XDR P. aeruginosa strain (susceptible to C/T but resistant to TZP) were ventilated for up to 72 h. Twenty-four hours after bacterial challenge, animals were randomized to receive 2-day treatment with either intravenous saline (untreated) or 25 to 50 mg of C/T per kg body weight (AEAT) or 200 to 225 mg of TZP per kg (IEAT) every 8 h. The primary outcome was the P. aeruginosa burden in lung tissue and the histopathology injury. P. aeruginosa burden in tracheal secretions and bronchoalveolar lavage (BAL) fluid, the development of antibiotic resistance, and inflammatory markers were secondary outcomes. Overall, P. aeruginosa lung burden was 5.30 (range, 4.00 to 6.30), 4.04 (3.64 to 4.51), and 4.04 (3.05 to 4.88) log10CFU/g in the untreated, AEAT, and IEAT groups, respectively (P = 0.299), without histopathological differences (P = 0.556). In contrast, in tracheal secretions (P < 0.001) and BAL fluid (P = 0.002), bactericidal efficacy was higher in the AEAT group. An increased MIC to TZP was found in 3 animals, while resistance to C/T did not develop. Interleukin-1ß (IL-1ß) was significantly downregulated by AEAT in comparison to other groups (P = 0.031). In a mechanically ventilated swine model of XDR P. aeruginosa pneumonia, appropriate initial treatment with C/T decreased respiratory secretions' bacterial burden, prevented development of resistance, achieved the pharmacodynamic target, and may have reduced systemic inflammation. However, after only 2 days of treatment, P. aeruginosa tissue concentrations were moderately affected.