The purpose of this study is to determine whether tifacogin is effective and safe in the treatment of patients with severe community-acquired pneumonia.

Inclusion Criteria:

• Diagnosis of community-acquired pneumonia supported by additional clinical, radiological, and microbiological evidence
• Pneumonia of sufficient severity to require ICU admission and management

Exclusion Criteria:

• Pregnancy
• Weight over 150 kg
• Patients at increased risk of bleeding
• Treatment with drotrecogin alfa or anticipated need for drotrecogin alfa
• Treatment with heparin or anticipated need for heparin