Infectious Diseases,  Internal Medicine



Are there risk factors for MRSA or pseudomonas (e.g. had MRSA or pseudomonas previously or was recently hospitalized and received IV antibiotics in the last 90 days)? Are there comorbidities e.g. chronic heart, lung, liver or kidney disease, diabetes mellitus, alcoholism or asplenia?

No: Amoxicillin 1 g tid OR Doxycycline 100 mg bid OR a macrolide if local pneumococcal resistance is < 25%. Macrolide options include: Azithromycin 500 mg on day 1 then 250 mg daily OR Clarithromycin ER 1g daily OR Clarithromycin 500 mg bid. Note that the strongest recommendation is for amoxicillin, followed by a conditional recommendation for doxycycline (there is limited data for oral doxycycline use for pneumonia, but it has broad spectrum action which is why it was chosen), and a conditional recommendation with the restriction of ensuring that there is low resistance for use of a macrolide. So, based on this, the first choice should be for amoxicillin 1g tid. Also note that some experts suggest starting on day 1 with 200mg for doxycycline (e.g. see, however, according to the IDSA 2019, there is no data so far that assesses whether this improves outcomes. Macrolides have been relegated to a third choice in many regions due to growing resistance by Streptococcus pneumoniae. However, when resistance is low and there is a contraindication to amoxicillin (e.g. penicillin allergy) then it is an option.

Yes: Requires stronger antibiotics, either beta-lactam antibiotic plus another class such as a macrolide or doxycycline, or monotherapy with a respiratory fluoroquinolone. Beta-lactam options: Amoxicillin/clavulanate (500mg/125mg tid OR 875mg/125mg bid OR 2g/125mg bid) OR Cepodoxime (200mg bid), OR Cefuroxime (500mg bid). There is no evidence from RCTs of any antibiotic choice above being superior to another (IDSA 2019). However, note amoxcillin/clavulanate has the most data and has been shown to be effective

Duration of antibiotics: The IDSA 2019 recommendations for antibiotic duration is that it should be guided by clinical stability i.e. normalization of vital signs, ability to eat, etc. However, that it should be no less than 5 days.

Case 1: 35 year old woman with fever and cough and sputum production for 4 days. Chest x-ray shows infiltrates. Otherwise healthy. Takes no medications. Normal BP, HR, and RR.

  • She has no comorbidities, and no risk factors for MRSA or pseudomonas mentioned. Dx: community acquired pneumonia. Tx: Amoxcillin 1g tid for 5 days with follow-up visit to ensure normalization of vitals and symptoms. Plus advise that if worsening symptoms or vitals or fever, patient should return to clinic.

Case 2: 28 year old man with fever and cough for 3 days. Chest x-ray shows infiltrates. Has beta-lactam allergy, specifically had anaphylactic reaction to penicillin 4 years ago. Normal BP, HR, and RR.

  • Dx: CAP with no risk factors or comorbidities. Tx: Beta-lactam allergy so doxycycline 100mg bid for 5 days, with scheduling of follow-up visit, and ensuring he knows to return if worsening symptoms.

Case 3: 48 year old man with fever and cough for 3 days. He was hospitalized 2 months ago for a staph infection and was given IV antibiotics. He has well controlled hypertension for which he takes chlorthalidone 50 mg daily. BP is currently 135 mmHg/ 85 mmHg. RR is 26 breaths/min. Normal mentation.

  • Dx: CAP with risk factors for MRSA/ pseudomonas and comorbidity (HTN). However, no suggestions of severe illness requiring hospitalization. (CURB65 – all factors normal except unknown BUN but even if it was high, outpatient treatment could still be considered because 1 point is still low risk). Tx:

Resources & References

IDSA 2019 Guidelines from ATS – pdf available here – Antibiotics & Common Infections 2016 – pdf available here