Medications

Dozens of antibiotics are available that can treat most cases of pneumonia in or out of the hospital, but it is sometimes difficult for the physician to select the best drug. Patients with pneumonia are given a specific antibiotic based on what type of organism is causing the disease. If the organism is unknown, the antibiotic is based on individual risk factors, such as age, health, and severity of the illness.

In determining the appropriate antibiotic, the physician must first answer a number of questions:

How severe is the pneumonia? Mild-to-moderate cases can be treated at home with oral antibiotics while severe pneumonia usually requires intravenous antibiotics administered in the hospital.
If the organism causing the pneumonia is not known, was the disorder community- or hospital-acquired? Different organisms are usually involved in each setting, and the physician can often use this information to guess the most likely organism causing the pneumonia.
If the organism is known, is it typical or atypical? Typical bacterial, community acquired pneumonias for example, are usually caused by Streptococcus pneumoniae, Haemophilus influenzae, or Moraxella catarrhalis, which have traditionally been treated with penicillin or other standard antibiotics. Such antibiotics, however, do not affect atypical organisms, such as Legionella, Mycoplasma, or Chlamydia. (These organisms are generally treated with a macrolide or possibly a newer quinolone.)
Does the patient have an impaired immune system, such as in AIDS? Antibiotics used to treat such patients may differ from those used in patients with healthy immune systems.

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Once an antibiotic has been chosen, there are still difficulties:

Individuals respond differently to the same antibiotic depending on age, health, size, and other factors.
Patients can be allergic to certain antibiotics, thus requiring alternatives.
Patients may harbor strains of bacteria that are resistant to certain antibiotics.

Antibiotic Treatments for Community-Acquired Pneumonia

For a more detailed discussion of the different types of antibiotics, see the "Antibiotic Classes" section below.

Many cases of community-acquired pneumonia are caused by S. pneumoniae, bacteria that usually respond to antibiotics known as beta lactams (which include penicillin,) and to macrolides. However, resistant strains of S. pneumoniae are increasingly common; most resistant strains respond to newer quinolines or ketolides.