From the Guidelines
Pneumonia is an inflammatory condition of the lungs caused by infection that leads to fluid accumulation in the air sacs (alveoli), with a pathophysiology that involves the invasion of pathogens, triggering an inflammatory response, and resulting in impaired gas exchange and potential complications. The pathophysiology begins when pathogens—typically bacteria like Streptococcus pneumoniae, viruses such as influenza, or fungi—enter the lower respiratory tract, bypassing normal defense mechanisms 1. Once these pathogens reach the alveoli, they multiply and trigger an inflammatory response, which includes increased blood flow to the affected area and the migration of white blood cells (particularly neutrophils) to fight the infection. The inflammation causes capillary leakage, allowing protein-rich fluid to enter the alveoli, which impairs gas exchange. Neutrophils release enzymes to kill pathogens but also damage lung tissue in the process. The alveoli fill with fluid, inflammatory cells, and debris, creating consolidation visible on chest imaging. This consolidation reduces lung compliance and creates a ventilation-perfusion mismatch, leading to hypoxemia. The body responds with increased respiratory rate and effort. In severe cases, the infection can spread to the bloodstream (bacteremia) or affect multiple organs. Recovery involves clearing the infection, resolving inflammation, and repairing damaged lung tissue, which typically takes several weeks even with appropriate antibiotic or antiviral treatment.
Some key points to consider in the pathophysiology of pneumonia include:
- The role of Streptococcus pneumoniae, Hemophilus influenzae, and other pathogens in causing pneumonia 1
- The importance of host factors, such as age, comorbidity, and immune status, in determining the severity of pneumonia 1
- The potential for pneumonia to lead to complications, such as bacteremia, sepsis, and respiratory failure, particularly in severe cases 1
- The need for prompt and effective treatment, including antimicrobial therapy and supportive care, to improve outcomes and reduce morbidity and mortality 1
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Pathophysiology of Pneumonia
The pathophysiology of pneumonia involves the disruption of lung homeostasis due to respiratory infections and lung injury 2. This can be caused by various microorganisms, including Streptococcus pneumoniae, which is the most common cause of community-acquired pneumonia worldwide 3.
Causes and Risk Factors
- Streptococcus pneumoniae is a frequent inhabitant of the upper airways in healthy hosts and can cause pneumonia when it invades the lower airways 3
- Atypical organisms are implicated in up to 40% of cases of community-acquired pneumonia diagnoses 4
- Comorbidities, previous antibiotic therapy, and nursing home residence can increase the risk of developing severe community-acquired pneumonia 5
Mechanisms of Disease
- The pathogen attempts to engage the host, proliferate, and invade the lower airways, while the host deploys innate and acquired cellular and humoral defences to prevent pneumococci from breaching tissue barriers 3
- The versatility of the genome of pneumococci and the bacteria's polygenic virulence capabilities make it challenging to control the microbe 3
Treatment and Prevention
- Combination antibiotic therapy, including β-lactams, macrolides, and fluoroquinolones, can achieve better outcomes compared to monotherapy 5
- Azithromycin 1g once daily for 3 days is at least as effective as amoxicillin-clavulanate 875/125 mg twice daily for 7 days in the treatment of adult patients with community-acquired pneumonia 6
- Doxycycline can be used as an alternative regimen in the treatment of severe community-acquired pneumonia in critically ill patients 4