Single vs Multiple Antibiotics in Community-Acquired Pneumonia

By Richard G. Wunderink, MD, FCCP; and Grant W. Waterer, MBBS, FCCP

Single vs Multiple Antibiotics

Given the difficulties with an etiologic diagnosis, the possibility of monotherapy for CAP requires at least two of three conditions to be present. The first is that even though diagnosis in a specific patient is infrequent, epidemiologic studies consistently find a narrow spectrum of etiologies. CAP in outpatients is typically caused by viruses, Chlamydia, Mycoplasma, and the pneumococcus. Therefore, monotherapy is the standard rather than the exception and none of the guidelines recommends combination therapy. In contrast, severe CAP is caused by a wide variety of microorganisms, and therefore combination therapy is usually recommended.

The second condition is that only a low incidence of antibiotic resistance is present or, if resistance is present, it has a low likelihood of adversely affecting outcome. Because outpatients typically had an excellent prognosis even in the preantibiotic era, macrolide- or tetracycline-resistant pneumococci are not a large concern. The reverse is true in patients with severe CAP, in whom microorganisms with high frequency of resistance to usual empiric therapy are more likely and associated with increased mortality.^13,14

The third is availability of antibiotics with good activity against the majority of CAP etiologies. In the recent past, the newer-generation macrolides fulfilled this criterion. Unfortunately, the significant increase in pneumococcal resistance makes this no longer true in many areas. The newest generation of quinolones clearly does meet this condition, with good activity against not only the pneumococcus, Chlamydia, Mycoplasma, and Legionella, but also Haemophilus influenza and S aureus. The adequacy of monotherapy with newer-generation quinolones is therefore the major controversy in the debate regarding single vs multiple antibiotic therapy.

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