Stanford Antimicrobial Safety & Sustainability Program

For the micro nerd:
Important beta-lactamases & nomenclature is shown in this table by Bush et al. Great review article here: pubmed.ncbi.nlm.nih.gov/32102899/

🔍 High-risk GNRs include:
-E. coli
-Klebsiella pneumoniae
-Klebsiella oxytoca
-Proteus spp.

📚 Reference: PMID: 39108079

💡 A: Many microbiology labs do not routinely perform ESBL -specific testing. Instead, since ESBLs hydrolyze third-generation beta-lactams, ceftriaxone non-susceptibility can be used as a proxy for ESBL production in certain GNRs that are at high risk for carrying ESBL:

🌟 ABX Pearl of the Day:

❓ Q: How do I tell if my gram-negative rod (GNR) is an extended-spectrum beta-lactamase (ESBL) producer?

#IDsky #medsky #meded #pharmsky #skyRX #AMSsky

📚
1. For more information, check the 🔥 new 2025 IDSA guidelines on complicated urinary tract infections: www.idsociety.org/practice-gui...

2. Nelson, Z., et al. UTI: A WikiGuidelines Group Consensus Statement. JAMA Netw Open. 2024;7(11):e2444495

💡 A: No, he does not have a complicated UTI. While it was previously thought that male gender, anatomic abnormalities, or immunocompromised status always indicated a complicated UTI, this is no longer supported by IDSA guidelines.(1,2) See Classification of UTI here:

🌟 ABX Pearl of the Day: UTI in males

❓ Q: My male patient with dysuria is growing E. coli (>100,000 CFU/mL) on urine culture. He has no systemic symptoms or signs of pyelonephritis or prostatitis. Does he have a complicated UTI?

#IDsky #medsky #meded #pharmsky #skyRX #AMSsky

📚 References:
Shenoy 2019. PMID: 30644987
Devchand 2019. PMID: 31937989
Drug Allergy 2022 practice update AAAAI/ACAAI
Blumenthal et al JACI IP 2017

📊 Check out our PCN allergy algorithm for more guidance!
(Note, ceph allergy algorithm not shown here)

🚫 Type II-IV delayed hypersensitivity reactions (DRESS, SJS/TEN) pose a higher cross-reactivity risk; beta-lactams should be avoided.

🤝 If there are multiple allergies or complex cases, consider a formal Allergy consult.

⚠️Type I (IgE-mediated) hypersensitivity reactions (e.g. anaphylaxis, wheezing, swelling) require assessing side chain similarity. Cefazolin has *no* side chain similarity to penicillin and is safe for most PCN allergies (exception below).

🩺 Non-severe reactions (e.g., nausea, self-limited rashes) are unlikely true allergies and shouldn't affect antibiotic choice.

⏳ Additionally, even IgE-mediated PCN allergy often wanes over time; ~80% of people are no longer allergic after 10 years, i.e. low risk.

🔍 General framework.
To assess risk, gather a thorough history of the reported allergy, focusing on:
-When the reaction occurred
-Timing of the reaction relative to antibiotic administration
-Type and severity of the reaction

💡 A: Yes! Cefazolin (and other cephalosporins) can be safely administered in patients with mild penicillin reactions.

🌟 ABX Pearl of the Day: penicillin allergies

❓ Q: My patient reports a reaction to penicillin (acute, self-limited rash) over 10 years ago. Can they safely receive cefazolin for their MSSA infection?
#IDsky #medsky #meded #pharmsky #skyRX #AMSsky

💡 A: Culture growth is classified as 1+ to 4+ based on how many quadrants of the plate show growth. Higher numbers indicate more quadrants involved, suggesting a higher inoculum.

📊 However, a higher growth number does NOT mean the organism is pathogenic.

❓ Q (Part 2): What does 4+ growth even mean?

💡 A: A positive sputum culture must be interpreted within the clinical context. If there’s no clear evidence of pneumonia, growth may represent colonization (common) and does not require treatment.

🔍 More growth does not necessarily correlate to a higher likelihood of pathogenicity.

🌟 ABX Pearl of the Day: sputum interpretation

❓ Q: My patient has 4+ growth of an organism on respiratory culture. Does this mean he has pneumonia?

#IDsky #medsky #meded #pharmsky #skyRX #AMSsky

⚠️ Nonetheless, caution should be exercised regarding ertapenem use in severely hypoalbuminemic patients, especially in the presence of sepsis.

📚 Additional References:
1. IDSA AMR guidance www.idsociety.org/practice-gui...
@idsainfo.bsky.social
2.Seazzu et al 2025 pubmed.ncbi.nlm.nih.gov/39976084/

🔍 It’s important to note that IDSA guidance is not a formal guideline; recommendations do not undergo the same rigorous process. A subsequent correspondence challenges the conclusions and calls for higher quality evidence to address the issue. (2) PMID 37721191

⚠️ Additionally, standard dosing of β-lactams may be inadequate in septic patients with increased renal clearance. The guidance authors also cite a retrospective study reporting greater mortality, though many confounding factors were present in the analysis. (1) PMID 25636928

📜 Evidence Summary:
A 2024 IDSA Guidance rec against the use of ertapenem in critically ill pts and those with hypoalbuminemia. This is based on PK data indicating rapid clearance of the free fraction of the drug, which has ~90% protein binding, potentially leading to inadequate fT>MIC PD targets.

📉 Hypoalbuminemia (<2.5 mg/L), higher CrCl, and higher MICs may lower the likelihood of achieving PK/PD targets for ertapenem. However, in patients who initially receive meropenem and are clinically stabilizing, it may be reasonable to consider de-escalation to ertapenem.

💡 A: Data is insufficient and conflicting, making it difficult to provide a clear answer. Clinicians should individualize decision-making based on patient-specific factors, such as:
-Source of infection
-Control of the infection
-Other relevant variables

🌟 ABX Pearl of the Day: ertapenem hypoalbuminemia

❓ Q: My ICU patient with hypoalbuminemia has ESBL E. coli pyelonephritis, resistant to PO abx. He improved (afeb, WBC WNL, off pressors) after 3d of meropenem. Should I avoid narrowing to ertapenem?

#IDsky #medsky #meded #pharmsky #skyRX #AMSsky

📚 References:
1.2017 IDSA Clinical Practice Guidelines for Healthcare-Associated Ventriculitis and Meningitis
2. Nau et al 2010. PMID: 20930076
3.CNS Infections and Antibiotic Selection: All Infection Sites Are Not Created Equal. PMID: 38113485

🤝 ID consultation is strongly recommended for patients with CNS infections to ensure appropriate management.

🚫 Conversely, piperacillin-tazobactam does not penetrate the CNS effectively, and there is insufficient data to support the routine use of cefazolin and ertapenem in meningitis cases.

🔍 Note that CNS dosing may be higher than for other indications. For specific CNS dosing notes, please consult our antibiotic dosing guide or Lexi-comp.