Ep 143: 5 Cases for Antibiotic Prophylaxis
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This is Katarina Heidhausen, Executive Editor of Harrison's Principles of Internal Medicine. Harrison's Pod Class is brought to you by McGraw-Hill's Access Medicine, the online medical resource that delivers the latest content from the best minds in medicine. And now, on to the episode. Hi, everyone. Welcome back to Harrison's Pod Class. We're your co-hosts. I'm Dr. Kathy Handy. And I'm Dr. Charlie Wiener, and we're joining you from the Johns Hopkins School of Medicine. Today, we're talking about antibiotic prophylaxis.

Kathy, today we're going to talk about antibiotic prophylaxis, and instead of one case, I'm actually going to present you with five cases.

All right, this is an important topic because antibiotics used for prophylaxis are commonly overused. What do you mean? Antibacterial prophylaxis is indicated only in selected circumstances. In all other cases, the risk or severity of the infection to be prevented should be greater than the adverse consequences of antibacterial therapy, and that includes the potential for selection of resistance. The timing and duration of antibacterial treatment should be targeted for maximal effect and minimal required exposure.

Okay, well, that's a good way to get to the cases for our discussion. So the question says, all of the following are appropriate uses of antibacterial prophylaxis except. So there's going to be four good cases and one bad case. Patient A is a three-year-old who receives amoxicillin and clavulinate for five days after a cat bite on the forearm that broke his skin and caused bleeding.

Option B is a 19-year-old college student whose roommate was diagnosed with acute meningococcal pneumonia and receives a single dose of oral ciprofloxacin. Option C is a 34-year-old with a mechanical mitral valve who receives a single dose of amoxicillin 30 minutes before removal of an impacted wisdom tooth. Option D is a 55-year-old with no nasal carriage of methicillin-resistant staph aureus

who receives topical mupiricin twice daily for five days prior to aortic valve replacement surgery and option e is a 73 year old undergoing knee replacement surgery who receives cefazolin one hour before surgery and daily for three days after the surgery these are all good so let's take them one at a time and we can go in order of age okay what about the toddler with a cat bite

Cat bites are notorious for their risk of infection. So prophylactic amoxicillin clavulonate, doxycycline, or amoxifloxacin for five days is reasonable. You may also consider the same regimen with a dog or a human bite, but cats pose the highest risk of domesticated animals. Also remember that if there's any uncertainty of the animal's rabies status, you must take that into consideration and would consider rabies vaccination too. No, not in this case. That was just the toddler pulling on the cat's tail.

Okay, I could see that happening. How about the college student? Yes, antibiotic prophylaxis is indicated in close contacts of patients with meningococcal meningitis. And that's due to the risk of transmission, the ease of prophylaxis, and the potential for devastating disease. And what is the recommended prophylaxis in those cases? A single oral dose of ciprofloxacin or two days of rifampin are the recommended regimens. Great. So A and B are true so far. How about the patient undergoing the dental procedure?

Also true, for dental procedures, pre-procedure antibacterial drugs are given to prevent transient bacteremia during the procedure and the seeding of certain high-risk cardiac lesions.

A mechanical mitral valve would qualify as a high-risk cardiac lesion. Someone with a history of endocarditis or congenital heart disease would also be a candidate for prophylaxis. And a single dose is okay? Yeah, a single oral dose about an hour before the procedure or even an IV dose 30 minutes before the procedure is adequate. Unless, of course, the procedure is very long. In that case, she may redose.

Also, while transient bacteremia is common with dental procedures, patients without high-risk cardiac lesions do not need prophylactic antibiotics. Okay, let's keep moving along. Option D talks about preventing MRSA infection. Does topical mupiricin work? In patients with nasal carriage of Staph aureus, preoperative decolonization reduces the rate of Staph aureus surgical site infections, and it's generally recommended. So yes, it does work. It's typically administered for three to five days before surgery.

Given its low toxicity, it is often used before elective surgery where hardware is being placed, such as a hip or a knee replacement. I know that many places that don't screen for nasal cariots just use the topical mupiricin before those kinds of surgeries anyway, right? Right. Okay, so option D is also true. That means option E is false. Tell me why.

Well, it is false, but there is some truth there. IV cefazolin is generally administered one hour before a clean cardiac, thoracic, neurologic, orthopedic, vascular, or plastic surgery, and that's to reduce the risk of surgical site wound infections.

But the important point is that additional dosing is not recommended after the incision is closed. If the surgery is long, another dose can be administered, but there's certainly no value in continuing this regimen for three days after surgery. And the choice of antibiotic?

Prophylaxis of surgical infections targets bacteria that may contaminate the wound during the procedure, and that includes the skin floor of the patient or the operating team and the air in the operating room. Okay, so to summarize, today's teaching points are that bacterial prophylaxis is indicated in particular situations where the risk of a complicating infection is much greater than the risk of antibiotics, and typically the course of antibiotics is prescribed and relatively short.

And you can find this question and other questions like it in the Harrison Self-Review book and more about this topic in the Harrison's chapter on treatment and prophylaxis of bacterial infections. Visit the show notes for links to helpful resources, including related chapters and review questions from Harrison's, available exclusively on Access Medicine. If you enjoyed this episode, please leave us a review so we can reach more listeners just like you. Thanks so much for listening.