Dr Liu Chung Ngar, Dorothy
Adventist Health Physician
Specialist in Respiratory Medicine
Hong Kong Adventist Hospital – Tsuen Wan
Hong Kong

Community-acquired pneumonia (CAP) is a common and potentially serious illness, particularly for older adults and those with comorbidities.¹ Timely initiation of appropriate antimicrobial therapy is needed for effective management of CAP.¹

Dr Liu provides an overview of the treatment strategies for CAP that are implemented at her medical institution in Hong Kong, and shares her clinical experience with fluoroquinolones for the treatment of CAP.

Q1. What are the treatment strategies for CAP in both outpatient and inpatient settings?

Antibiotic treatment is recommended for all patients with CAP, including both outpatients and inpatients. Treatment success is dependent on prompt delivery of antibiotics, appropriate for the likely causative organisms and clinical severity. The common causative pathogens of CAP are Streptococcus pneumoniae and respiratory viruses.^{2, 3}

For CAP patients in outpatient settings, empiric regimens are usually designed to target atypical pathogens, for which a beta-lactam plus a macrolide such as erythromycin, clarithromycin or doxycycline are used. The treatment provided in the inpatient setting differs from the outpatient setting owing to differences in the causative pathogens. The inpatient setting can be further divided into general ward care and intensive care unit (ICU) admission. In the general medical ward, in addition to treating the pathogens mentioned earlier, we must ensure that that the treatment targets Staphylococcus aureus and gram-negative bacteria such as Klebsiella pneumoniae. It is also important to keep in mind the possibility of infection with methicillin-resistant S. aureus (MRSA) and/or Pseudomonas infection when selecting an initial regimen. For patients without suspicion of MRSA or Pseudomonas infection, we generally use combination therapy with a beta-lactam plus a macrolide, or monotherapy with a respiratory fluoroquinolone such as levofloxacin.⁴ For patients with strong suspicion for pseudomonal infection, we use a combination therapy including an antipseudomonal beta-lactam plus an antipseudomonal fluoroquinolone such as levofloxacin. For patients with strong suspicion of MRSA infection, we add vancomycin or linezolid for their anti-MRSA activity on top of the above therapies.⁵

For CAP patients admitted to the ICU, the timing of antibiotics is crucial for patients who present as critically ill – we generally start antibiotic therapy within one hour of presentation. The process for antibiotic selection is similar to that used for patients admitted to the general medical ward, however, owing to the severity of illness in this population, we do not use monotherapy. As for general ward patients with CAP, empiric regimen should take into account the risk factors for MRSA and/or Pseudomonas infection. For patients without MRSA or pseudomonal infection, we treat with a stronger beta-lactam agent (such as augmentin or meropenem), plus a macrolide (azithromycin or clarithromycin), or a beta-lactam plus a respiratory fluoroquinolone (such as levofloxacin).⁴ For patients with MRSA or pseudomonal infection, we treat with combination therapy of an antipseudomonal beta-lactam (such as piperacillin-tazobactam, meropenem or imipenem) plus an antipseudomonal fluoroquinolone such as levofloxacin.⁴

Q2. Are there any differences between the clinical approaches to the treatment of CAP patients with critical illness compared to those with stabilised illness?

The main difference between clinical approaches is whether monotherapy or combination therapy is used. We generally do not use monotherapy for patients in ICU; combination regimen must be given intravenously as soon as possible, and ideally within one hour of admission of the patient who is critically ill. In the general ward setting, with patients of stabilised illness, we typically use monotherapy with a respiratory fluoroquinolone if the patient is unable to tolerate any beta-lactam agents.

Q3. What is the role of fluoroquinolones in the treatment of CAP in your clinical practice?

A fluoroquinolone is an appropriate alternative for CAP patients who cannot receive a beta-lactams or has penicillin allergies. For hospitalised CAP patients receiving a levofloxacin regimen, higher non-split dosing of 500 – 750 mg daily are usually recommended. Caution should be noted for patients with impaired renal function, for whom a possible dosing regimen will be a loading dose of 500 mg, followed by 250 mg every 48 hours.

Q4. How common is penicillin allergy among CAP patients, and what are your recommended treatment approaches for such patients?

Approximately 10% of patients report some type of allergy to penicillins.⁶ However, penicillin allergy may be over-reported; less than 1% of the population are truly allergic to penicillins, and approximately 80% of those who were once allergic to the drug lose their sensitivity to penicillin after 10 years.⁶ Despite that, the diagnosis of “penicillin allergy” is usually accepted without obtaining history of the reaction, and penicillins are withheld from these patients. Skin testing for penicillin allergy is recommended to determine if a patient with CAP is truly allergic to penicillins before initiation of antibiotic therapy. For patients who are truly allergic to penicillins, broad-spectrum and non-beta-lactam antibiotics are used as alternatives. For hospitalised penicillin-allergic patients with suspicion of anaerobic infection, alternative medications include either a combination of a third-, fourth- or fifth-generation cephalosporins plus metronidazole or a carbapenem, depending on the severity of allergy.

Q5. In recent years, aspiration pneumonia (defined as lower respiratory tract infection caused by aspiration or inhalation of irritant substances) has been garnering attention in the clinical setting, owing to the increasing elderly population.⁷ Based on your clinical experience, how common is aspiration pneumonia, and what is your approach to its treatment?

Aspiration pneumonia is a common infection in elderly adults and is increasing in prevalence owing to the aging population in many countries. There are two major aspiration syndromes: bacterial pneumonia and chemical pneumonitis. Hereafter, only bacterial aspiration pneumonia is discussed. In early studies, anaerobic bacteria have traditionally been known to be the predominant cause of aspiration pneumonia. However, more recent data suggest aerobic bacteria may predominate. Hence, it is important that we treat patients with aspiration pneumonia with a regimen that ensures antimicrobial coverage of both anaerobic and aerobic bacteria, and administer the regimen intravenously, especially in severe cases. For patients admitted to the hospital but who are not critically ill, we suggest ampicillin-sulbactam rather than a cephalosporin-based regimen, for wider anaerobic coverage. For outpatients, we usually prescribe amoxicillin-clavulanate.

References

1. Kolditz M, Ewig S. Dtsch Arztebl Int. 2017;114(49): 838–848.
2. Lo WL, et al. J Dent Sci. 2019 Sep;14(3):241–247.
3. Terpenning MS, et al. J Am Geriatr Soc. 2001 May;49(5):557–63.
4. Doyle RL, et al. Am J Respir Crit Care Med. 1995 Dec;152(6 Pt 1):1818–24.
5. Warner MA, et al. Anesthesiology. 1993 Jan;78(1):56–62.
6. Centers for Disease Control and Prevention. Citing websites: Is it Really a Penicillin Allergy. Available from: https://www.cdc.gov/antibiotic-use/community/pdfs/penicillin-factsheet.pdf. Accessed 26 August 2022.
7. Zhang Q, et al. Front Public Health. 2021;9:771154.