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    Interpreting culture report: MIC and resistance

    A recent culture was positive for klebsiella pneumoniae that recurred after a course of ciprofloxacin (PO). I have two sets of questions about the culture report:

    1. Gentamicin had a MIC of 4 ug/mL; meropenem of 1; and ceftriaxone of 1. The urologist suggested a course of IV gentamicin as a possibility to consider. Is a MIC of 4 kind of high? Is it "borderline sensitive" or "extremely sensitive" to IV gentamicin? Why not one of the other IV drugs with lower MICs? I understand of course that MICs are not comparable across drugs, what I want to know, generally, is how can I interpret the clinical significance of a MIC for gentamicin in particular (and more generally for other drugs)? What specific reference would I use?

    2. The bug is resistant to cefaclor (PO) and cefoxitin (IV), but sensitive to cefazolin (IV); ceftriaxone (IV); ceftazidime (IV); and cefepime (IV). ESBL resistance was detected.

    Is the bug resistant or sensitive to Keflex (cephalexin) PO? (Other drugs listed did not seem relevant).

    In general, how do I determine if a bug in a culture is resistant or sensitive to a drug when that drug is not explicitly named in the culture report?

    #2
    each antibiotic is different. As long as report says Sensitive it is ok to prescribe for the organism. The lab knows the breakpoint for each antibiotic and they determine if sensitive, resistant or resistant. I make rounds with infectious disease doctors twice a week. They are the most knowledgeable. ESBL+are capable of hydrolyzing penicillins, cephalosporins and monobactsms. You can also give IM gentamicin and daily dose so that it could be given at home. Meropenem is great but reserved for those only sensitive to meropenem-it is considered a big gun! And usually saved when nothing else is sensitive. And we need to use the “penems “for numerous other possible infections. Outpatient ‘s can’t have meropenem. Inpatient, I order but all doctors have to get clearance from our SCI ID doctor. Try www.ncbi.nlm.nih.gov/PMC6428495/. CWO
    The SCI-Nurses are advanced practice nurses specializing in SCI/D care. They are available to answer questions, provide education, and make suggestions which you should always discuss with your physician/primary health care provider before implementing. Medical diagnosis is not provided, nor do the SCI-Nurses provide nursing or medical care through their responses on the CareCure forums.

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      #3
      Originally posted by xsfxsf View Post
      A recent culture was positive for klebsiella pneumoniae that recurred after a course of ciprofloxacin (PO). I have two sets of questions about the culture report:

      1. Gentamicin had a MIC of 4 ug/mL; meropenem of 1; and ceftriaxone of 1. The urologist suggested a course of IV gentamicin as a possibility to consider. Is a MIC of 4 kind of high? Is it "borderline sensitive" or "extremely sensitive" to IV gentamicin? Why not one of the other IV drugs with lower MICs? I understand of course that MICs are not comparable across drugs, what I want to know, generally, is how can I interpret the clinical significance of a MIC for gentamicin in particular (and more generally for other drugs)? What specific reference would I use?

      2. The bug is resistant to cefaclor (PO) and cefoxitin (IV), but sensitive to cefazolin (IV); ceftriaxone (IV); ceftazidime (IV); and cefepime (IV). ESBL resistance was detected.

      Is the bug resistant or sensitive to Keflex (cephalexin) PO? (Other drugs listed did not seem relevant).

      In general, how do I determine if a bug in a culture is resistant or sensitive to a drug when that drug is not explicitly named in the culture report?

      You do not know if a bug in a culture is resistant or sensitive to a drug when the drug is not explicitly named. In general, they must test that drug to be sure.

      As the RN said, every antibiotic concentration is different for what determines whether the bug is sensitive to it or not. Do not focus on those numbers. Just focus on the conclusion - Sensitive (S), Intermediate (I) or Resistant (R).

      If you know there is a specific drug you want them to test, the doctor should write that on the urine culture script. Alternatively, the doctor can call the laboratory once they have the sample and ask them to add on additional tests. If you aren't that sick, and can continue to keep your symptoms in check with Dmannose/ Cranberry (is it EColi?), methenamine, vitamin C, microcyn instillations etc... then you might be able to hold out? But this is a decision to make with your doctor. Waiting too long to treat a UTI can sometimes lead to severe illness, sepsis, and admission to the ICU!

      My Dad has UTIs with highly resistant ESBL bugs that often are resistant to most oral antibiotics. We always ask them to check for sensitivity to the old antibiotic fosfomycin, as most of the bacteria are not resistant to this antibiotic because it is rarely used.

      Keflex is in the family of antibiotics called cephalosphorins. If the bacteria is resistant to any of the cephalosphorin family members, it will probably be resistant to Keflex too. Your bug is resistant to some cephalosphorins but sensitive to others.... ??? But I would not try Keflex just because you hope it would work. Ask your doctor to see if they can add on a test for sensitivity to fosfomycin (and Keflex if you want! But I am not optimisitic....).

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        #4
        Fosfomycin and also minocycline. But now I think most If they still have the urine, they could check it. What are your symptoms?
        It is not sensitive to Keflex(Cephalexin) is done. It is in the cephalasporin group 1- they tested all 3 generations (classifications). Cefpodoxime might kill it, hard to tell without looking at the complete report. A specific antibiotic is not checked unless requested or they test a specific drug but we order something in that group, not necessarily that drug, as they are in groups.

        CWO
        The SCI-Nurses are advanced practice nurses specializing in SCI/D care. They are available to answer questions, provide education, and make suggestions which you should always discuss with your physician/primary health care provider before implementing. Medical diagnosis is not provided, nor do the SCI-Nurses provide nursing or medical care through their responses on the CareCure forums.

        Comment

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