Choice of Antibiotics: Basic Principles
Determining the type and the duration, as well as deciding whether and when to switch to oral therapy, is complicated by the failure to identify the causative pathogen in the majority of patients with community-acquired pneumonia. Even when carefully sought, a putative pathogen is documented in only one-half or less of cases.[25,26,27,28] This is a clinical reality that limits the value of many textbook treatment recommendations. In most cases, when a specific microbiologic diagnosis is not established, the physician chooses the therapy empirically, based on epidemiologic data. When an etiologic pathogen is identified (either initially or at a later time in the disease course), the antibiotic spectrum can be narrowed. When no inciting pathogen is discovered, empiric antibiotics are continued.
In either scenario, the patient should be evaluated for switch to oral antibiotics once clinical improvement is noted -- if factors associated with increased morbidity and mortality are absent (Table I).
The oral antibiotic chosen for switch therapy should encompass the same antibacterial spectrum as the intravenous agent. In addition, the oral regimen should have a good dosing schedule and a low adverse reaction profile to ensure completion of therapy. The dosing schedule is of particular importance because this affects patient compliance. Using an oral antibiotic with a frequent dosing schedule is associated with reduced compliance and greater potential medication error than using one with a once or twice a day dosing regimen.[29,30,31]
No one antibiotic regimen has been definitively shown superior to others in switch therapy. Knowledge of local epidemiology and resistance patterns should guide both the initial intravenous empiric therapy and the subsequent oral antibiotic. For example, if a patient is treated with an intravenous 2nd or 3rd generation cephalosporin, and no pathogen is identified, then switch therapy may be initiated with an oral 2nd or 3rd generation cephalosporin. If the patient is treated initially with an intravenous beta-lactam/beta-lactamase inhibitor combination and no pathogen is identified, then switch therapy may be initiated with an oral beta-lactam/beta-lactase inhibitor combination. In the case of a patient initially treated with intravenous erythromycin, switch therapy can be with either oral erythromycin or with one of the newer macrolides that have less complex dosing regimens. Studies favoring the newer macrolides suggest better compliance, few side effects, and similar clinical cure rates.[32,33,34] If a specific pathogen is identified, then switch to an oral antibiotic that covers that pathogen is necessary. For example, if penicillin-sensitive Streptococcus pneumoniae is identified in the blood, oral penicillin may be appropriate.
In some cases, blood culture may identify a "noncovered" organism in a patient who is clinically responding. In this setting, the literature does not clearly indicate whether it is necessary to cover all identified organisms; the conservative approach is to do so.
Medscape General Medicine. 1998;1(3) © 1998
Cite this: Antibiotic Therapy in Community-Acquired Pneumonia: Switch and Step Down Therapy - Medscape - May 01, 1998.