Why vancomycin is not the answer

As I tutor of medical students I have noticed a few trends. I wanted to share just one of them today. Specifically I want to talk about a very specific antibiotic that many students think is the answer for so many infectious disease questions. That antibiotic is vancomycin. Now, just to clarify, I am not shaming anyone for not knowing. On the contrary, I want to help you to understand the right times to use vancomycin, so that you can get those pesky MCQ questions correct. More importantly this knowledge will help you when making decisions on how to help your patients. We need to start with answering the question, what is vancomycin?

Vancomycin is a renally excreted inhibitor of peptidoglycan synthesis which is used to build the bacterial cell wall. Without this the bacteria dies which by definition makes vancomycin bactericidal. It accomplishes this by stopping D-Ala-D-Ala groups from attaching to the growing chain; however, gram negative bacteria cell walls are thick. Gram negative bacteria, such as E. coli, have porin proteins that act as tunneled highways by letting small molecules in and are too small to allow bulky molecules such as vancomycin through. If you remember back to molecular biology class 70% of UTIs are caused by E. coli. That being said is the first point is vancomycin is not used to treat UTIs unless the organism involved is gram positive AND you do not have other options.

Now you may be saying that vancomycin has activity against MRSA and you would be right. Vancomycin is used in cases of suspected or confirmed MRSA infection as well as serious skin/bone (osteomyelitis) infections caused by staphylococci; however, have you ever noticed that for sepsis and endocarditis the guidelines say to switch to a synthetic penicillin (PCN) if culture results show MSSA infection or a non-staphylococci infection? This is partly to stop cross resistance from developing as well as the fact that vancomycin is not as effective as synthetic penicillins, but also because vancomycin is very toxic. Red man syndrome is one toxicity that leads to an IgE independent mast cell degranulation. This causes wheals and urticaria primarily on the upper torso, neck, and arms. Rarely this can cause angioedema. The risk of this can be reduced by anti-histamine prophylaxis and decreasing the infusion rate. Drug fever is another possible problem that complicates the clinical course, but nowhere near as much as the feared neutropenia.

Vancomycin also does a great job of working synergistically with aminoglycosides to create help destroy the patient’s ears and kidneys (ototoxicity and nephrotoxicity). Again you might say, but a patient can live without their kidneys on dialysis right? If we ignore the fact that lifelong dialysis is life changing to say the least then yes you can survive on dialysis; although, vancomycin is not removed by dialysis. One dose is enough for 7 days while on dialysis. This is important as many of the toxicities, and the benefits, are dose dependent.

The route of entry is also important to consider. Vancomycin is used IV, but is not released into the colon this way. For moderate/severe C. difficile infection or previous C. difficile infection you should give vancomycin orally. Watch for trick questions that will have both IV and oral (PO) as possible answers. This also adds the duality that vancomycin given IV does not alter the gut flora and does not cause diarrhea. With this being said there is one other area where vancomycin is important and that is when GBS treatment is required in a pregnant woman allergic to PCN.

That is all for this post, so if you want a free and non-obligatory consult on how to study for the USMLE, NBME exams, or MCCEE or any other medical exam check out http://www.mcceetutoringservices.com/contact and send me an email! If you liked this article just say so in the comments below!

References

Golan, D. E., Tashjian, A. H., & Armstrong, E. a. (2012). Prinicples of Pharmocology: The Pathophysiologic Basis of Drug Therapy Third Edition. Philadelphia, PA: Lippincott Williams and Wilkins.

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