The American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA) have recently published an update to the previous guidelines on the management of community-acquired pneumonia (CAP) in adults.^1,2

The new guidelines address 16 specific areas including antibiotic recommendations for empiric treatment of the common bacterial CAP. These recommendations refer to bacterial pathogens including Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Staphylococcus aureus, Legionella species, Chlamydia pneumoniae and Moraxella catarrhalis. Generally, recommendations on the use of antibiotics in CAP depend on the inpatient-outpatient setting, presence of comorbidities, severity of the infection and involvement of multi-drug resistant (MDR) pathogens. For the management of MDR pathogens, the panel presents separate recommendations – particularly for methicillin-resistant S. aureus (MRSA) and Pseudomonas aeruginosa.

In outpatient adults without comorbidities or risk factors for antibiotic-resistant pathogens, amoxicillin 1 g three times daily or doxycycline 100 mg twice daily is recommended. In an update to the previous guidelines, macrolide use may only be considered in settings with low incidence of pneumococcal resistance to macrolides (<25% of pneumococcal isolates).^1,2 Meanwhile, in outpatient adults with comorbidities, broader-spectrum antibiotics are recommended due to a higher probability of poor outcomes and risk of antibiotic resistance. The use of either amoxicillin/clavulanate or a cephalosporin is recommended in combination with either a macrolide or doxycycline (Table 1). Another option is monotherapy with a respiratory fluoroquinolone. Both options are recommended with no order of preference.

Table 1. Antibiotic use in outpatient adults with comorbidities*

*Comorbidities include chronic heart, lung, liver or renal disease; diabetes mellitus; malignancy; or asplenia. OD: once daily; BID; twice daily; TID: Three times daily. Adapted from Metlay et al. 2019

The inclusion of fluoroquinolones as the broad-spectrum monotherapy of choice is based on their efficacy profiles from several studies,^3-8 very low resistance rates, activity across both typical and atypical strains, oral bioavailability, convenience of monotherapy and relatively low associated incidence of serious adverse event.

For inpatient adults with non-severe CAP and an absence of risk factors for MRSA or P. aeruginosa, recommendations include either combination therapy with a β-lactam and a macrolide, or monotherapy with a respiratory fluoroquinolone (Table 2). In case of contraindications to both macrolides and fluoroquinolones, a combination of a β-lactam and doxycycline may be considered. For hospitalized adults with severe CAP and an absence of risk factors for MRSA or P. aeruginosa, the panel recommends a β-lactam/macrolide combination or a respiratory fluoroquinolone (Table 2). The criteria for assessing CAP severity from the 2007 guidelines are maintained for the current update.^1,2

Table 2. Antibiotics use in inpatient adults

* The risk factors include prior respiratory isolation of MRSA or P. aeruginosa, or recent hospitalisation with parenteral antibiotics in the last 90 days. OD: once daily; BID; twice daily; TID: Three times daily. Adapted from Metlay et al. 2019

In addressing the treatment for adults with CAP and risk factors for MRSA and P. aeruginosa, the panel recommends abandoning the use of the healthcare-associated pneumonia (HCAP) categorisation as a guide for selecting extended antibiotic therapy since the method was demonstrated to be inaccurate in predicting high prevalence of antibiotic-resistant bacteria.^9-11 Instead, the panel recommends that extended antibiotic therapy for MRSA and P. aeruginosa should only be considered if patients present with locally validated risk factors for either pathogen. In these cases, blood and sputum cultures are recommended and if the results are negative, the treatment is de-escalated at 48 hours.

Regarding the duration of antibiotic therapy for CAP, the panel recommends that antibiotic treatment should be continued until the patient achieves clinical stability (i.e., resolution of vital sign abnormalities, ability to take food orally and normal mentation) and for no less than 5 days. However, in suspected or proven cases of MRSA or P. aeruginosa, the panel recommends a treatment duration of 7 days. When switching from parenteral to oral antibiotics, either the same agent or an agent in the same class should be used.

Among other recommendations on antibiotic use is the suggestion to only consider additional antibiotic therapy for anaerobic bacteria in aspiration pneumonia if there is suspicion of lung abscess or empyema. The panel also recommends initiating standard antibiotic therapy in adults who are suggestive of CAP (based on clinical examination and radiography) and who test positive for influenza – due to the high prevalence of co-infections and potentially serious complications of influenza. The antibiotic therapy may be discontinued in stable patients at 48 to 72 hours if the available evidence demonstrates absence of bacterial pathogens.

Summary

There are several changes in the recommendations for antibiotics use compared with previous guidelines. The use of macrolide monotherapy and doxycycline as standard therapy has been limited to conditional recommendations. Respiratory fluoroquinolones remain the only first-line monotherapy recommended in outpatient adults with comorbidities and in inpatient adults with non-severe CAP, while β-lactams remain one of the options for standard CAP treatment. Both treatments are recommended in combination for inpatient adults with severe CAP. The consideration of adding extended-spectrum antibiotic for MRSA and P. aeruginosa should be based on the presence of locally validated risk factors for the pathogen, rather than using the previous risk factors listed under the HCAP categorisation.

References

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