USMLE Antibiotic choice

[Beastkiller]

Come across this question in uworld and am confused.

Question: patient came in with obvious sign for IE and was given empiric vancomycin, then blood culture turned out to be strep. Virindans. what's next step?

Correct answer: IV ceftriaxone

BUT, isn't this 3rd generation cephalosporin cover mostly gram negative bug? Why choose this one?

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[RLSGrasshopper]

Yes, Ceftriaxone has as good array of GN coverage. However, let's not forget it is a beta-lactam (penicillin-like) antibiotic. Since the blood culture came back positive for a specific organism, in this case a Streptococcal sp. which is susceptible, it is better to give this more narrow antibiotic. Does this explanation help, or naaaaaaaah?

 

[Beastkiller]

Yes, Ceftriaxone has as good array of GN coverage. However, let's not forget it is a beta-lactam (penicillin-like) antibiotic. Since the blood culture came back positive for a specific organism, in this case a Streptococcal sp. which is susceptible, it is better to give this more narrow antibiotic. Does this explanation help, or naaaaaaaah?

That being said any generation of cephalosporin will do? I think I am confused because in FA, it says 3rd generation is effective to gram negative bugs.

 

[RLSGrasshopper]

That being said any generation of cephalosporin will do? I think I am confused because in FA, it says 3rd generation is effective to gram negative bugs.

Yes, almost any generation of Cephalosporin can help, but keep in mind some generations are better to use than others, due to coverage variability for certain bacterial pathologies. For instance, it is better to use Cephalexin for skin infections if we know it is a non-methicillin resistant Gram Positive (GP) bacteria, while Ceftriaxone is pretty much used for alot of things especially GP bacterial meningitis. Some Cephalosporins are given PO, IM, &/or IV only, keep that in mind as well. Read a little upon it in the MTB series, you will see that antiobiotic treatment is very selective. That's why it is always important to first start with empiric treatment while you wait for the blood culture, bc when it comes back positive for a certain bacterial species, you can go ahead and choose the right one.

As far as FA is concerned, I think it should have also put in somewhere about Cephalosporin being a beta-lactam antibiotic. Just make a note of it.

 

[Beastkiller]

Yes, almost any generation of Cephalosporin can help, but keep in mind some generations are better to use than others, due to coverage variability for certain bacterial pathologies. For instance, it is better to use Cephalexin for skin infections if we know it is a non-methicillin resistant Gram Positive (GP) bacteria, while Ceftriaxone is pretty much used for alot of things especially GP bacterial meningitis. Some Cephalosporins are given PO, IM, &/or IV only, keep that in mind as well. Read a little upon it in the MTB series, you will see that antiobiotic treatment is very selective. That's why it is always important to first start with empiric treatment while you wait for the blood culture, bc when it comes back positive for a certain bacterial species, you can go ahead and choose the right one.

As far as FA is concerned, I think it should have also put in somewhere about Cephalosporin being a beta-lactam antibiotic. Just make a note of it.

Thank you for clarifying this for me. Appreciate it!

 

[RLSGrasshopper]

Thank you for clarifying this for me. Appreciate it!

Word son, got you killah