When an otherwise healthy adult develops acute bronchitis, the rule is still to withhold antibiotics since more than 90% of cases are viral.9 Exceptions include infection with Chlamydia, Mycoplasma, and Bordetella pertussis (these organisms cause fewer than 10% of acute bronchitis cases).6 When these atypical agents are suspected, therapy with a macrolide or doxycycline is not inappropriate. (Such laboratory investigations as polymerase chain reaction or culture for B. pertussis and serology for Mycoplasma may be prudent in the setting of an outbreak but are impractical and unhelpful in individual cases.)
For the other 90% of acute bronchitis cases, the patient should be advised that the infection is likely to be self-limited. Treatment is supportive and includes rest, fluids, and time. A bronchodilator can help with wheezing (even if the patient is not known to have asthma).10 Obviously, it is important to rule out pneumonia first. The presence of fever, tachypnea, tachycardia, consolidation, or rales should trigger further evaluation with chest radiography. Rapid antigen tests for influenza are also helpful when this diagnosis is suspected and can further reduce inappropriate antibiotic use.
One question that frequently arises in clinical practice is whether treating bronchitis with an antibiotic will prevent pneumonia. For a number of years, the prevailing wisdom was that it did not. Data now both support and qualify this. In fact, in a British study that looked at the use of antibiotics to prevent pneumonia in patients with acute chest infections, the number needed to treat was 39 above age 65 but closer to 100 for younger age groups.11 In the 30 days following diagnosis, pneumonia developed in 4% of those not treated with antibiotics but in only 1.5% of those who received them. Surprisingly, smokers did not appear to have different outcomes than nonsmokers.
Of course, common sense and clinical judgment support the early use of antibiotics in patients whose pulmonary function is otherwise limited (e.g., patients who are immunocompromised in any way or have such chronic diseases as cystic fibrosis).
Chronic obstructive pulmonary disease
Acute exacerbations of chronic obstructive pulmonary disease should be treated with oral steroids and broad-spectrum antibiotics, according to published guidelines.12 The fluoroquinolones levofloxacin and moxifloxacin are superior to such first-line drugs as amoxicillin, doxycycline, and TMP/SMX.13
Any one of the following oral regimens is recommended for uncomplicated pneumonia (Figure 2) in patients who do not require hospitalization, have no significant comorbidities, and/or have not used antibiotics within the past three months, and in locations where there is not a high prevalence of macrolide-resistant bacterial strains: azithromycin (500 mg on day 1 followed by four days of 250 mg a day, three days of 500 mg a day, or a single 2-g dose), clarithromycin XL (two 500-mg tablets daily for five days or until afebrile for 48-72 hours), or doxycycline (100 mg twice a day for 7-10 days).14 Erythromycin, though effective and inexpensive, is not well tolerated, requires multiple daily doses, and may cause fatal arrhythmias (especially when used with other drugs).
The use of fluoroquinolones in ambulatory community-acquired pneumonia without comorbid conditions or recent antimicrobial use is discouraged unless there is a high prevalence of strongly macrolide-resistant Staphylococcus pneumoniae in the local community. If a respiratory fluoroquinolone is used, experts advise gemifloxacin (Factive) 320 mg daily, levofloxacin 750 mg daily, or moxifloxacin 400 mg daily for a minimum of five days.
These agents are expensive, however, and combination therapy with a beta-lactam effective against S. pneumoniae and a macrolide or doxycycline is an acceptable alternative (e.g., high-dose amoxicillin 1 g three times daily or amoxicillin-clavulanate 2 g twice daily or cefpodoxime 200 mg twice daily or cefuroxime 500 mg twice daily PLUS either a macrolide [azithromycin 500 mg on day 1 followed by four days of 250 mg a day or clarithromycin 250 mg twice daily or clarithromycin XL 1,000 mg once daily] or doxycycline 100 mg twice daily). Treatment should continue for a minimum of five days.