Episode 88- Can we treat staph aureus bacteremias with oral antibiotics?

Hello and welcome to Episode 88 of ER-Rx- a podcast tailored to your clinical needs. I’m your host, Adis Keric. Have you ever had a patient with a staph aureus bacteremia and wondered if you could treat it with oral antibiotics? This question does come up from time-to-time, and I thought it would be a good idea to review a fantastic article published by Michael Dagher and his friends in Open Forum Infectious Diseases.

Staph aureus is a very common cause of hospital and community-acquired bacteremia. Typically, IV antibiotics are used to treat these bacteremias given their high risk of complications, unlike gram-negative bacteremias which are often times easier to treat- and typically with shorter durations of antibiotics and even step-down therapy to oral antibiotics (like I talked about back in Episode 76). Unlike these gram-negative bacteremias, there is much more controversy on whether or not we can treat uncomplicated staph aureus bacteremias with oral antibiotics. Treating with oral antibiotics could cut costs by up to 50% and it could even cut readmissions for the adverse drug events and catheter complications that are common with prolonged durations of IV antibiotics.

But is treating staph aureus bacteremias with oral antibiotics ever a good idea? First, let’s define our patient population. The IDSA defines “uncomplicated” as being afebrile and having negative follow-up blood cultures > 48 hours after the index positive blood culture. Patients also have to be without metastatic sites of infection, endocarditis, and they must not have any prosthetic devices such as pacemakers. Everyone else is considered a “complicated” case and shouldn’t be treated with oral antibiotics and they are not the topic of this episode. Also, we’re talking about early step-down therapy only- meaning that patients must have been treated with IV antibiotics for a minimum of 7-10 days first.

There are arguments both for and against considering using oral antibiotics for these patients. If you’re considering it, there are only a handful of oral antibiotics that could even be considered for use.

Linezolid is one of them. It’s 100% bioavailable and can give you up to 85% cure rates for staph aureus bacteremia. In some small trials linezolid had similar clinical and microbiological cure rates as continued IV therapy- again after first starting out with IV linezolid and then switching to oral. Overall, this is the only antibiotic with some decent clinical data supporting it as a step-down to complete a course of therapy for patients with uncomplicated staph aureus bacteremia.

The fluoroquinolones are also sometimes considered- and although they have great bioavailability, they haven’t been studied much in this setting. One reason is obvious; staph aureus, and especially MRSA, has high resistance to fluoroquinolones. One of the newer agents, delafloxacin, may have some better activity against staph and MRSA, but again data is lacking on using even this agent. Overall, given the lack of data and the high risks of using fluoroquinolones in general, this doesn’t seem like a good idea.

Bactrim is another one that can be considered, but when we look at clinical data, it actually did worse than IV vanco for staph aureus infections- even when the Bactrim was given IV. Adding rifampin may improve your odds of clinical cure- but until more data comes out, in general we should not step-down to Bactrim. Just for the sake of completeness, clindamycin, doxycycline, and beta-lactams in general shouldn’t be considered for step-down therapy.

So really we have 3 possible antibiotics, and only one of those, linezolid, is actually backed by some sliver of decent data. This makes the argument against stepping down to oral antibiotics much stronger. Let’s get into that for a second.

First, there just isn’t enough great data for oral step-down therapy in general, and the consequences of undertreating a bacteremia can be severe. It just doesn’t seem like a good risk to take.

Also- it’s been proven that it’s very hard for us to differentiate between a patient with a “complicated” vs an “uncomplicated” bacteremia. In one trial, almost 1/3 of patients thought to have an “uncomplicated” bacteremia actually had a complicated case. One of the reasons for this discrepancy is that the complications and diagnoses of metastatic infections- like epidural abscesses, osteomyelitis, and even endocarditis- are often delayed and sometimes missed.

And in general, uncomplicated staph aureus bacteremias are pretty rare- with some trials showing that complicated cases are thirty times more common than uncomplicated ones.

To wrap up, we don’t have much evidence to guide treatment of staph aureus bacteremia in general, let alone guide therapy on using oral antibiotics to treat it. But we can consider the use of oral step-down antibiotics such as linezolid on a case-by-case basis, involving ID experts and shared decision making with the patient. And remember, this should only be considered after 7-10 days of IV antibiotics in very stable, uncomplicated cases. This is never something that should be given up-front out of the ER setting, or without discussing with an ID expert.

As always, thank you so much for your time, and thank you for wanting to learn more about pharmacotherapy. If you have any comments or anything you’d like to add to this episode, please give me a shout out on the @errxpodcast Instagram page, or reach out to me personally on errxpodcast.com- I’d love to respond to all comments and criticisms.

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