Those of you who have read my chapter on MRSA in the 3rd Edition of the Handbook of Lower Extremity Infections (haven’t you all by now?!) or listened to me lecture about MRSA know that I am less than happy with what I perceive to be the overuse of trimethoprim/sulfamethoxazole (TMP/SMX, Bactrim® or Septra®) used empirically against this bug.  It seems to be first line therapy by just about every Emergency Department, Urgent Care, Primary Physician or anyone else treating skin and skin structure infections. My primary objections, spelled out in detail on pages 332-333 of the book, are based on published reports of adverse events when using this drug.  It is not benign when used in the dosages and durations that may be needed to treat CA-MRSA.  In particular, I have concerns with allergies, renal problems, neurological AEs and drug-drug interactions.  Well, a brand new paper just published in the June 28, 2010 issue of Archives of Internal Medicine by Antoniou, Gomes, Juurlink, et. al. entitled Trimethoprim-Sulfamethoxazole Induced Hyperkalemia in Patients Receiving Inhibitors of the Renin-Angiotensin System gives one more reason for concern.

(Link to PubMed Abstract:

This was a population based, nested control study of a population >66 year olds who were receiving Angiotensin Converting Enzyme Inhibitors and various antibiotics.  The numbers were impressive.  This was a 14 year study with 4148 identified admissions involving hyperkalemia.  To quote the Conclusions, it was found that “Compared with amoxicillin, the use of TMP/SMX was associated with a nearly 7 fold increased risk of hyperkalemia-associated hospitalization.  No such risk was found with the use of comparator antibiotics”.

I still believe that if you have a mild CA-MRSA infection or are considering a “step down” from either vancomycin or linezolid, then doxycycline or minocycline is frequently preferable over TMP/SMX for therapy. Sure, I have used TMP/SMX in some cases.  One of the more recent that comes to mind was a patient with CA-MRSA plus Stenotrophomonas maltophilia.  Using TMP/SMX gave me a single agent I could use to cover both bugs.  I don’t want to “trash” TMP/SMX but given all of the data out there on potential problems with it, I would encourage you to chose it with a full understanding of the issues surrounding it and not just because you see others prescribing it so freely and randomly.