Rationale for empirical regimens for CAP in adults

Australian studies show that penicillin-based regimens are effective and safe for most adults with low- or moderate-severity community-acquired pneumonia (CAP). For further information, including empirical antibiotic regimens, see Low-severity CAP in adults or Moderate-severity CAP in adults.

Adults with high-severity CAP requiring intensive care support have a high risk of adverse outcomes if they do not receive appropriate initial treatment. Therefore, broader-spectrum empirical antibiotic therapy is recommended initially for these patients until the results of investigations are available, even though penicillin-susceptible Streptococcus pneumoniae is the most common cause of high-severity CAP. For further information, including empirical antibiotic regimens, see High-severity CAP in adults.

Further background on the empirical antibiotic regimens for CAP in adults follows.

• Cefuroxime has better antipneumococcal activity compared to cefalexin or cefaclor. If an oral cephalosporin is required to treat CAP for patients who have had a nonsevere (immediate or delayed) hypersensitivity reaction to a penicillin, use cefuroxime.
• At the recommended dosage, intravenous benzylpenicillin, amoxicillin and ampicillin have similar efficacy, but benzylpenicillin is preferred for intravenous therapy because it has a narrower spectrum of activity.
• Ceftriaxone is not recommended for empirical treatment of moderate-severity CAP unless the patient has a nonsevere (immediate or delayed) hypersensitivity reaction to a penicillin, because S. pneumoniae strains with high-level penicillin resistance remain rare causes of CAP in Australia.
• Widespread use of quinolones has been associated with the development of resistant pathogens and with Clostridioides difficile (formerly known as Clostridium difficile) infection. Consequently, moxifloxacin is reserved for patients with CAP who have had a severe (immediate or delayed)¹ hypersensitivity reaction to a penicillin. When a quinolone is necessary for empirical therapy for CAP, monotherapy with moxifloxacin is preferred because it has better antipneumococcal activity than ciprofloxacin.

If a pathogen is identified, use directed antibiotic therapy. If a viral aetiology is determined, stop antibiotic therapy. Some antibiotics have poor or uncertain efficacy for the treatment of pneumonia, so should not be used even if susceptibility is reported (eg daptomycin, tigecycline).