Empiric Antibiotics and SSRRH Antibiogram (Patel, 9/25/24)

 Many thanks to Omi Patel, PharmD and head of our SSRRH pharmacy for an excellent and important talk on Empiric Antibiotics and the SSRRH Antibiogram. A recording of her presentation is available HERE. 

My notes:

Empiric antibiotics should be chosen based on many different factors:

• patient characteristics (age, comorbidities, recent hospitalization, etc)
• site of infection
• pharmacokinetics
• evidence-based guidelines (e.g. IDSA, John's Hopkins, Sanford guide)
• facility specific guidelines (CPMC, UCSF)
• clinical pathways (most recent possible)
• local antibiogram (which is what this talk focused on)

At SSRRH, there is a system-wide order set that offers empiric antibiotic options based on site of infection. It is available under order sets. Do NOTE these are not specific to SSRRH, and our local antibiogram should be consulted if using these order sets.

As noted above, the hospital specific antibiogram is essential to good antibiotic stewardship. Omi pointed out that for bacteria for which we have less than 30 isolates, the data is less reliable and trends over time (i.e. looking back at old antibiograms) may be helpful in choosing the empiric treatment. You can see on the antibiogram below, the numbers in red reflect the number of isolates from 2023 of that particular bacteria. Reach out to the pharmacist to help you with this. The "30 isolate rule" is a National standard so applies to any antibiogram

Gram Negative Organisms at SSRRH

trends over time for Morganella at SSRRH

Last year, at SSRRH 64% of Gram Negative Organisms were E Coli. Other more commonly isolated organisms include Klebsiella, Pseudomonas, Proteus and Enterobacter.

For general medical patients, >85% susceptibility is considered adequate for empiric antibiotics.

For ICU patients, the higher the better, >90% susceptibility is preferred.

Empiric UTI Treatment

In 2023, SSRRH changed to using Cefoxitin, a second generation cephalosporin, as our first line for empiric parenteral UTI treatment.

Of note, our current rates of susceptibility of E Coli to ciprofloxacin (80%), levofloxacin (77%) and Bactrim (79%) mean that we should NOT be using them for empiric treatment for UTI.

Omi reminded us of a few common clinical circumstances:

• Despite common practice, ceftriaxone does not concentrate well in the urine as cefoxitin. Ceftriaxone should not be first line for UTI treatment
• Once culture results return, use the specific data to drive antibiotic treatment moving forward
• If a patient has had a recent history-- meaning in the last 120 days) of infection at the same site, use that information (and NOT the antibiogram) to drive your empiric antibiotic choice
• ESBL is a form of resistance that presents in gram negative bacteria. 
• The CTX-M gene (aka Ceftriaxone resistance) is a surrogate marker for ESBL 
• Sutter labs will not specifically report out an ESBL organism, so LOOK for ceftriaxone resistance as a surrogate marker for ESBL organisms
• If you suspect an ESBL organism, do NOT use Zosyn, any cephalosporin for empiric treatment. Your best choice is a carbapenem

• For pseudomonas aeruginosa, the only oral abx for this organism locally is ciprofloxacin, and based on 2023 antibiogram, it is currently only 83% sensitive
• do NOT use levofloxacin (77% sensitive)

Empiric Staph Aureus 

• MRSA resistance to clindamycin has been consistently high since 2017 (around 59%)
• do NOT use clindamycin for MRSA coverage
• Resistance to TMP-SMX is increasing in Santa Rosa (>16% resistance rate)
• Doxycycline sensitivity (currently 95%) is significantly higher than tetracycline (68%).
• Tetracycline is NOT a good surrogate marker for doxy against MRSA. Therefore, susceptibilities should be reported separately.
• Doxycycline is a good local choice for empiric MRSA coverage

Empiric Group B Strep (GBS)

• Local GBS is resistant to clindamycin 50% of the time, GAS is resistant 25% of the time
• Clindamycin should never be used to empirically cover GBS in a pregnant woman without sensitivities 
• Unless sensitivity is known, linezolid is preferred over clindamycin to inhibit toxin production (usually just 3 days duration)

Restricted Antibiotics

At SSRRH, certain antibiotics are restricted to ID approval with the intention of preventing misuse/overuse and preserving susceptibility over time. This technique has proven successful in limiting our local resistance. The restricted antibiotics include: