Dozens of antibiotics are available for treating pneumonia, but selecting the best drug is sometimes difficult. Patients with pneumonia need an antibiotic that is effective against the organism causing the disease. When the organism is unknown, "empiric therapy" is given, meaning the doctor chooses which antibiotic is likely to work based on factors such as the patient's age, health, and severity of the illness.
In determining the appropriate antibiotic, the physician must first answer a number of questions:
Once an antibiotic has been chosen, there are still difficulties:
Joint guidelines issued in 2007 by the Infectious Disease Society of America and the American Thoracic Society (ITSA/ATS) recommend that mild CAP in otherwise healthy patients be treated with oral macrolide antibiotics (azithromycin, clarithromycin, or erythromycin).
Many patients with heart disease, kidney disease, diabetes, or other co-existing conditions may still be treated as outpatients. However, they should be given a fluoroquinolone (moxifloxacin, gemifloxacin, or levofloxacin) or a beta-lactam (preferably high-dose amoxicillin or amoxicillin-clavulanate), plus a macrolide, unless they live in an area with high S. pneumoniae resistance to macrolides.
Research has not pinpointed an exact duration of antibiotic therapy. Current recommendations call for 7 - 10 days of treatment for S. pneumoniae and 10 - 14 days for Mycoplasma pneumoniae and Chlamydia pneumoniae. However, some research suggests that patients with mild-to-moderate community-acquired pneumonia may be successfully treated with 7 days or less of antibiotics. The shorter treatment may increase patient tolerance, and improve the likelihood that patients will stick to the treatment regimen. It will also help limit the growing problem of antibiotic resistance.
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 -- Gram-positive 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 fluoroquinolines such as levofloxacin (Levaquin), gemifloxacin (Factive), or moxifloxacin (Avelox). Another common cause of community-acquired pneumonia is H. influenzae.
In addition, other important causes of CAP, particularly in younger people, are atypical bacteria, which respond to macrolides (erythromycin, clarithromycin, or azithromycin), ketolides, or newer fluoroquinolones.
Antibiotic treatment for CAP is determined by a number of factors, including:
Treatment options can include a single drug, such as levofloxacin or doxycycline, or combination treatment, such as a macrolide administered with a beta-lactam.
Antibiotics taken by mouth are generally enough for patients whose CAP is mild enough to be treated at home. Intravenous antibiotics are required for hospitalized patients with CAP. Antibiotic therapy should be given for a minimum of 5 days -- longer if the patient still has a fever and more than one sign of continuing severe illness.
A broad range of antibiotics is available for treating hospital-acquired pneumonias. Factors that may determine the choice of an antibiotic include:
There are not as many choices for treating viral pneumonia. Oseltamivir (Tamiflu) and zanamivir (Relenza) have been the recommended drugs for influenza A or B infections, but many strains of influenza A have become resistant. Their use is only recommended if they are started in the first 48 hours of symptoms. Taken early, these medications may be effective in reducing symptoms and duration of illness. [See In-Depth Report #94: Colds and influenza. ]
Patients with viral pneumonias are at risk for what are called "superinfections," which generally refers to a secondary bacterial infection, usually caused by S. pneumoniae, S. aureus, or H. influenzae. Doctors most commonly recommend treatment with amoxicillin-clavulanate, cefpodoxime, cefprozil, cefuroxime, or a respiratory fluoroquinolone if these secondary infections occur.
Patients with pneumonia caused by varicella-zoster and herpes simplex viruses are usually admitted to the hospital and treated with intravenous acyclovir for 7 days.
No antiviral drugs have been proven effective in adults with RSV, parainfluenza virus, adenovirus, metapneumovirus, the SARS coronavirus, or hantavirus. Treatment is largely supportive, with patients receiving oxygen and ventilator therapy as needed.
Treatment of RSV in Children. Ribavarin is the first treatment approved for RSV pneumonia, although it has only modest benefits. The American Academy of Pediatrics recommends this drug for children who are at high risk for serious complications of RSV.
Most antibiotics have the following side effects (although specific antibiotics may have other side effects or fewer of the standard ones):
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