So, let's talk about that last one linezolid.
They're used in drug-resistant
gram-positive cocci infections like,
Methicillin-Resistant Staph Aureus,
Penicillin Resistant Strep-Pneumo
and Vancomycin-Resistant Enterococcus.
They bind to the 50 S ribosomal
unit as I had mentioned before,
there is no cross resistance with
other protein synthesis inhibitors
and they're reserved for
multi-drug resistant agents.
Now, I want to just show you a
picture from an echocardiogram.
This is a tricuspid valve, so on the
left side you can see the tricuspid valve
and you can't really see any kind of vegetation.
On the right where the green arrow is pointing,
you can see a large vegetation
on one of the tricuspid valves.
This person has obviously,
a fairly severe endocarditis
and a valvular vegetation,
because it's the tricuspid valve,
you know, it's the right side,
it's probably involved with some
kind of intravenous drug abuse.
This patient had multiple resistant infection
was actually treated quite
successfully with this drug.
Now, in terms of toxicity.
Toxicity of this drug include
thrombocytopenia and neutropenia.
This particular patient
which was managed conservatively.
Unfortunately, you can also
have serotonin syndrome.
So, remember that, if you
know, your IV drug abusers
also tend to be on antidepressants,
there's a high correlation there
and if you're using this antibacterial agent
you may actually induce a serotonin syndrome.
So, please go back to your psychiatry lectures
and take a good look at serotonin syndrome,
so, that you understand it.
The streptogramins are a
combination of two medications,
they tend to be bactericidal, with
really good post-antibiotic effects.
They are active against MRSA, VRSA
and other resistant enterococci.
Now, E. faecalis is resistant to these agents,
because they have a very unique
efflux transport mechanism.
Which is kind of cool, these
organisms have actually evolved
a way of getting rid of streptogramins
from the inside of their cytoplasm.
In terms of toxicity and adverse events.
You often get a very painful injection
site, you can get myalgia and arthralgias.
Remember that these agents are potent inhibitors
of CYP450 3A4, so therefore if
you remember your other lectures,
they will increase plasma levels of drugs like,
cyclosporine, diazepam and warfarin.
Chloramphenicol has a very distinct structure.
There's actually no other drugs in its class,
so, it's on its own.
It has wide distribution, it's a
non-polar molecule as you can see,
so, it crosses the blood-brain
barrier and the blood uterine barrier.
It's inactivated in the liver and
it has minimal renal excretion.
It's bacteriostatic against Haemophilus,
Neisseria, the Bacteroides species.
It's also used as a backup
drug against Salmonella,
pneumococcal disease and meningococcus.
It can also be used topically quite often as well.
It is not active against chlamydia species.
The resistance is through a
plasmid-mediated formation of an enzyme,
called an acetyltransferase,
that inactivates that drug.
The toxicity especially for
topical use, is direct irritation,
you can also get super
infections like candidiasis,
remember that chloramphenicol
does not work against candida.
Aplastic anemia, is a potential side effect,
that's relatively rare about 2.5 per 100,000,
it is irreversible and can be fatal though.
The one thing that i want you to
remember about chloramphenicol,
is something called, “Gray baby syndrome,”
It is going to be on your exams,
at some point in your career.
That is where you get anemia,
cyanosis, cardiovascular collapse,
it affects neonates, especially
those who are premature
and it may be linked to a deficiency
in the hepatic glucuronyltransferase.
So, it's something important to be aware of
and to know.