g., Y-27632 defensins) through reduced levels of extracellular proteins and coagulation products but at least it is most likely that there are processes involved that are independent of anticoagulant activity. Additional research is needed to elucidate the mechanisms by which plasma-derived AT affects bacterial outgrowth, inflammatory response and migration of neutrophils into the pulmonary compartment.Our data suggest that therapy with plasma-derived AT might benefit patients with S. pneumoniae pneumonia, but additional pre-clinical studies are needed to examine this hypothesis before this therapy is to be tested in patients. The coagulation system plays an important role in containing infections and certain microorganisms even induce profibrinolytic mechanisms to escape from being contained in a fibrin clot [33].

Coagulation and inflammation are pivotal host defence mechanisms, and interference with these pathways should be performed with great care because this may also have deleterious effects. Indeed, previous preclinical studies have demonstrated interfering with the initial procoagulant response in Pseudomonas aeruginosa pneumonia in rats and mice is potentially dangerous [34,35].Systemic anticoagulant affects of nebulized anticoagulantsSystemic administration of anticoagulant compounds substantially increases the risk of bleeding. In the clinical trial with rh-aPC in patients with severe sepsis, the incidence of serious bleeding was higher in the treatment group than in the placebo group (3.5% versus 2.0%) [9].

In a randomized controlled trial with AT the occurrence of bleeding events in patients with severe sepsis was even more pronounced, especially when AT was combined with heparin (22.0% versus 12.8%) [15]. In the present study with inhaled anticoagulants, none of the investigated agents, with the exception of danaparoid, affected systemic coagulation suggesting inhaled anticoagulants may reduce the risk of systemic bleeding.The systemic effects on coagulation of nebulized danaparoid suggest that this agent is leaking from the pulmonary compartment into the circulation after local administration. Danaparoid is a relatively small molecule of 5.5 kDa which is more likely to leak into the circulation as compared with rh-aPC (56 kDa) or plasma-derived AT (58 kDa). Heparin is also a small molecule (8 kDa); however, it did not seem to leak into the circulation in our experiments.

This may be due to binding of heparin to pulmonary endothelial cells and alveolar Drug_discovery proteins and metabolism by heparinases [36]. A recent clinical study of nebulized heparin in patients with ALI; however, did show systemic effects in the highest concentration used [37], although this dose was up to 40% higher than the dose we used in our animal study.Previous studies on anticoagulant strategies for pneumoniaOur results are in line with data from previous animal studies.