HY lecture notes:
You need to know standard community-acquired pneumonia (CAP) empiric Tx is a macrolide, usually azithromycin.
This will cover both Strep pneumo as well as atypicals such as Mycoplasma, Chlamydia, and Legionella.
Roxithromycin is sometimes used in kids instead of azithromycin, although the USMLE won’t go there. Just making a point.
If the patient has been on Abx during the past three months or is immunocompromised, a fluoroquinolone such as levofloxacin may be used instead of the macrolide. The USMLE won’t make you distinguish. The bottom line is you need to be aware that azithromycin and levofloxacin are frequently given for CPP empiric Tx.
If the patient is in sepsis + has strep pneumo infection (confirmed or likely), then give a third-generation cephalosporin. This is really HY.
If it’s a kid <1 year, cefotaxime is often used. If >1 year, cefriaxone is standard. On one of the IM forms, cefotaxime was the answer in an 11-month old with sickle cell. On NBME 8 for 2CK, the answer was ceftriaxone in a 6-year-old.
Likely S. pnuemo infection = kid with sickle cell who missed penicillin prophylaxis (answer = third-gen ceph, not penicillin to Tx).
Confirmed S. pneumo infection = sputum sample grows gram (+) diplocci.
Sepsis = SIRS + source of infection.
SIRS = 2 or more of the following:
- Temp <36 or >38C.
- WBC <4,000 or >16,000.
- RR 20 or higher.
- HR 90 or higher.
Macrolides can cause GI disturbance (diarrhea or constipation), which is the number-one reason for non-adherence. They can also prolong the QT-interval. They also inhibit P-450 (but not azithromycin).
Fluoroquinolones cause cartilage damage (Achilles tendonitis) and cannot be taken with foods, especially the divalent cations iron and calcium, which decrease oral bioavailability.
If they say the patient has a pneumonia that presents as right-lower lobe consolidation with dullness to percussion (lobar), the answer is S. pneumo.
If they say the patient has bilateral interstitial infiltrates, the answer is Mycoplasma.
If they say right-lower lobe interstitial infiltrates seen on CXR, the word “interstitial” wins over right-lower lobe location; answer = Mycoplasma.
If they say immunocompromised patient who went to a conference recently, the answer is Legionella. Legionella is also the answer if someone has diarrhea + hyponatremia alongside the pneumonia.
Summary:
Outpatient empiric Tx for CAP: azithromycin (1st-line) or fluoroquinolone.
If patient is admitted to hospital for CAP (non-ICU): fluoroquinolone, OR beta-lactam + macrolide (e.g., azithromycin).
If patient is admitted to hospital for CAP (ICU): beta-lactam, PLUS either macrolide or fluoroquinolone.
If hospital- or ventilator-acquired pneumonia (HAP/VAP), must cover for S. aureus + Pseudomonas: Tx = broad-spectrum Abx coverage; various answers are vancomycin + cefepime; vancomycin + ceftazidime; pipericillin-tazobactam; meropenem. Bottom line is: know that the difference between CAP and HAP/VAP is that the latter two require coverage for S. aureus + Pseudomonas.
