October 18th, 2013

Back to School: Top Questions from “ID in Primary Care”

i am a generic question guyWe hold an annual post-graduate course entitled “Infectious Diseases in Primary Care”. In this 2.5 day course, we ID doctors do our best to address the concerns of clinicians on the front lines — those doing primary care.

And each year, we get some great questions. Like these:

Question: I work at a university health center, and each year we have several hundred visiting students from countries that routinely give BCG immunization. We continue to do PPDs (tuberculin skin tests, TSTs) because they are cheaper, but there are tons of positives. Should we switch to an IGRA (interferon gamma release assay)?
Answer:  If ever there were an indication to use IGRAs over TSTs, this is it! Think of the potential money, time, and aggravation you’d ultimately save. Once you switch to IGRAs for those with a BCG history, here’s what you won’t have to do:   1) track down the people who don’t return to have their skin test read; 2) explain to the BCG-immunized with the reactive skin test that we don’t consider BCG in this country when we interpret TSTs (Note:  No one who’s received a BCG believes us; they think we’re out of our minds.); 3) get a chest X-ray in those with reactive TSTs from BCG alone;  4) prescribe unnecessary preventive therapy for that same group. Sounds like a good trade off to me.

Question: For skin infections, shouldn’t we double the dose of trimethoprim-sulfamethoxazole [that’s not what he said — he said “Bactrim”] to two double-strength tablets twice daily?
Answer: I’m not sure where this one came from — and it’s a widely held belief — but as far as I know, there are no definitive data supporting a double dose of TMP-SMX for skin infections. Plus, some of the toxicity of TMP-SMX is dose-related, and those “double-strength” tablets are gigantic. Notably, this randomized study used the standard dose (1 DS twice-daily), and this one used variable weight-based dosing. If someone knows why the higher dose is anecdotally so popular, let me know! Which reminds me — what should we call this drug?  I generally frown on using trade names unless absolutely necessary, but “Bactrim” (or the less-commonly-used “Septra”) are vastly superior to the mouthful that is the generic name.  Some say “cotrimoxazole”, but what is that? Please weigh in by voting in the poll below, and providing your comments. And FYI, I say “trim-sulfa”, but hardly anyone does.

Question:  Do you need to check serologies before giving the zoster vaccine if someone says they never had chicken pox as a kid?
Answer:  Nope — the good news is that per the zoster vaccine guidelines, we can consider anyone born before 1980 in the United States to be varicella immune. And the last time I checked, everyone older than 60 (for whom the vaccine is indicated) was born before 1980, though you may wish to double-check my math.

Question:  Do you recommend repeat testing for C diff after the patient has been treated?
Answer:  Certainly not if he/she is improving, as a repeat positive with any of the myriad C diff tests out there is quite common shortly after C diff treatment, and treating improving/resolved C diff with antibiotics is a bad move. So when would you check again? I find repeat C diff testing helpful in someone with a recent episode who’s now having vague symptoms (e.g., not a florid relapse), as a negative result suggests that it’s probably post-infectious GI issues (alteration of normal flora would be the broad generalization of what causes this) rather than a relapse of C diff.

Question:  When is next year’s course? I’d love to attend.
Answer:  October 1-3, 2014. And we guarantee the New England weather will be perfect and the Red Sox will be in the playoffs.

What do you call trimethoprim-sulfamethoxazole?

View Results

20 Responses to “Back to School: Top Questions from “ID in Primary Care””

  1. D. Branam says:

    The 2011 IDSA guidelines (Clin Infect Dis 2011; 52: e18-55) recommend a SMX-TMP dosage of 1-2 tablets BID. The 2011 and 2009 Sanford Guide (the only copies I could get my hands on at the moment) echo this same recommendation. Data supporting the 2 tablets dosage have been sparse. In addition to the articles you’ve cited, I offer Antimicrob Agents Chemother. 2011 December; 55(12): 5430–5432, an observational case-control study that found no difference between the 1 and 2 tablet regimens. As you’ve mentioned, adverse effects (such as hyperkalemia) are dose related, and since so many of my patients are also on ACEIs/ARBs, I only recommend 1 tablet BID.

  2. Jonathan Blum says:

    The genesis of “2 ds bid” might have been Markowitz N et al. Ann Int Med 1992; 117: 390. This trial compared IV TMP/SMZ with vancomycin in 101 IDUs with S. aureus infections (including both MRSA and MSSA, and some with bacteremia or endocarditis). The results have been interpreted in myriad ways, but that’s not the issue here. The dose they used was TMP 320/SMZ 1600 q12 hr. That’s the IV equivalent of 2 ds bid (probably a little more, since the oral bioavailability is not quite 100%). Only about a third of their patients had skin and soft tissue infections. I don’t know how they chose the dose. A later French study (Stein A et al. AAC 1998; 42: 3086) used even higher doses (8-9 ds/daily for a 70-kg man) for infected orthopedic devices, a somewhat different kettle of fish. Another recent study by the same group (Ameen S et al. JAC October, 2013) provided pharmacokinetic evidence to support 2 ds tid, but I have seen only the abstract. So while I cannot say what the “right” dose is for skin infections (for abscesses it’s often zero), the Markowitz paper may have set that standard.

  3. Rosalie Auster says:

    The name I use depends on context: another provider or pharmacist: Bactrim. For patients, I explain that it’s 2 drugs in one pill, a sulfa and another called trimethoprim, trade names Bactrim and Septra and are they allergic to
    any of them.

  4. Rosalie Auster says:

    Where/when will I find the announcement for next year’s course?

  5. Gabe says:

    Just say “TMP Sulfa”

    • Paul Sax says:

      Just say “TMP Sulfa”

      Nice! I have heard that one, along with “Trim Sulfa” (that was was the late Merle Sande used to say), which is even shorter.


  6. Alex says:

    How about “TIMP SOX”

  7. Adam says:

    Cotrimoazole seems to be an international trade name, as I haven’t seen it is US literature but only articles from outside the US.

  8. Barry Saver says:

    I also tend to use TMP-sulfa, or trimethoprim-sulfa. But sometimes, alas, “Bactrim” with patients.

  9. Henry says:

    I’ve seen a lot of providers treat NON-purulent cellulitis with TMP-SMX and Cefadroxil (for MRSA and strep, respectively). Do we really need to cover MRSA in non-purulent cellulitis, given that Group A Beta-hemolytic Strep (GABHS) is the issue here (with occasional MSSA, which Cedadroxil will cover)?

    • Paul Sax says:

      Do we really need to cover MRSA in non-purulent cellulitis, given that Group A Beta-hemolytic Strep (GABHS) is the issue here (with occasional MSSA, which Cedadroxil will cover)?

      Henry, not according this study:

      Clin Infect Dis. 2013 Jun;56(12):1754-62. doi: 10.1093/cid/cit122. Epub 2013 Mar 1.
      Clinical trial: comparative effectiveness of cephalexin plus trimethoprim-sulfamethoxazole versus cephalexin alone for treatment of uncomplicated cellulitis: a randomized controlled trial.
      Pallin DJ, Binder WD, Allen MB, Lederman M, Parmar S, Filbin MR, Hooper DC, Camargo CA Jr.


  10. Allan Wilke says:


  11. KWC says:

    Since fellowship, I have said trim/sulfa and it has worked very well. My colleagues (ID and otehrwise) know what I’m talking about and I don’t have to use a brand name. Works like pip/tazo to avoid saying Zosyn every time.

  12. John GILBERT says:

    Co-trimoxazole is a British usage, like co-amoxiclav, co-codamol 8/500 (codeine & paracetamol), co-codamol 30/500 and so on. It serves a useful purpose since all these combinations have been around for decades.

  13. Bill Pereira says:

    Co-trimoxazole (or cotrimoxazole) is the official generic name given to the fixed (1:5) combination of trimethoprim-sulfamethoxazole by WHO as well as by the European and British Pharmacopoeiae, among others. The USAN (U.S. Adopted Name) of pharmaceuticals often differs from the rest of the world’s terminology, e.g. acetaminophen vs. paracetamol.

  14. DrAnand Arvind Deshmukh says:

    Nice one
    Shall You convey me dates and cost for attending workshop?
    I am from india.

  15. Anonymous says:


  16. Sulfametoxazol-Trimetroprim is called “Bactrim” here in Brazil also, but we all call it plain old “Sulfa”. 🙂

    And about the course … you guys should start looking at a Coursera or eDX to make this course online :)))


  17. Dr H says:

    Co-trimoxazole sounds too much like “clotrimasole”, which you will use to treat your female patients after using TMP-Sulfa

  18. Dr. Linds says:

    Yay! I submitted my choice of “trim-sulfa” under “other” – and the late Dr. Merle Sande was our attending/discussant at numerous stump-the-stars type conferences when I was a med student at the University of Utah in the late 90’s. Good times in ID history…

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Paul E. Sax, MD

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