Let's talk about chapter four immune. This is penicillins and
before I can really start talking about penicillins, I have to talk just a tiny bit of organic chemistry
about a beta-lactam ring. The first thing that you'll notice is that there's nothing circular here,
so the beta-lactam ring is really referring to
this over here where you have this ring structure and the importance of this ring structure is that a
beta lactamase and -ase meaning enzyme, a beta lactamase
can destroy that ring. This is the penicillin ring and
a Bacteria can create a beta lactamase to destroy the ring. Penicillinase
is the name we give to an enzyme that destroys the ring in a penicillin and
cephalosporinase is an enzyme that destroys the ring in a cephalosporin,
but again,
just keep that image in mind - that a Bacteria can destroy this ring and make the penicillin, and when we go to
cephalosporins, the cephalosporin inactive.
The four drugs we'll go over are an aminopenicillin
which has IV and IM forms, ampicillin, and you'll see this term generic only.
What they're saying is that it's been so long on
the market that we don't even remember what the brand name is. I'm sure ampicillin
IV/IM had a brand name when it was by itself.
In combination, it's
Unasyn, but by itself I don't remember what the brand name was, so we just put generic only ampicillin
PO forms brand name was Principen.
Aminopenicillin, PO
amoxicillin, and that was brand Amoxil
when I was in the pharmacy, and then the aminopenicillin beta-lactamase inhibitor is
amoxicillin, the amin penicillin and then the beta-lactamase inhibitor is clavulanate, and together
they augment the activity of amoxicillin, and that's why it has the name
Augmentin
Cephalosporin, the third generation is beta lactamase resistant.
Because it's third-generation, it also tends to move towards gram-negative coverage and it also tends to get into the
CNS. when we're talking about third generations in general, that's the way to remember it is that third generation,
three things change - gram positive to gram negative coverage,
CNS, and then resistance to beta-lactamaces.
Cephalosporins begin with 'cef-', but this company was so
confident in their product that they said it is Omnicef,
'omni-' meaning everything, so the cephalosporin covers everything, which obviously isn't exactly true.
It does cover something that's beta lactamase resistant, and we'll see how that kind of fits in.
We'll go to our practice question one, and we'll use drug classes here.
'A patient can't take anything PO and
PO again means per os,
literally 'by the opening' in Latin,
but we just translate it to by mouth, and requires a parenteral, which is actually
etymologically para which means outside of and then enteral, which is really anything from the mouth to the anus, so
outside of the GI tract in general
you can think of like parenteral, so that's outside of what's normal
as a way to remember para, so it's a broad spectrum penicillin antibiotic we're looking for. Which one do you choose?
Now when we have drug classes. It's really easy. A)
Aminopenicillin IV/IM,
B) Aminopenicillin by itself or PO,
C) Aminopenicillin with beta-lactamase inhibitor and D) third-generation cephalosporin.
Well, if it's parenteral, it's going to be IV/IM, and we see the '-cillin' stem for the aminopenicillin, but let's go to
The answers and just put it there. That's the correct route.
The aminopenicillin amoxicillin will only come PO,
and we'll see that in a second. Augmentin only comes PO, and the third-generation cephalosporin because it has the 'cef'- won't be a penicillin.
This doesn't make quite as much sense until we get to the drug names themselves.
So we don't change the the question, all we change is
that we're taking the drug classes - now the drugs themselves and that we underline
the stems.
Ampicillin,
this comes IV/IM. There is a PO form but this is the correct route.
Amoxicillin unfortunately only comes PO.
Amoxicillin/clavulanate also only PO, and
cefdinir, it's not a penicillin and it
does come
PO,
but that doesn't really help us here as well.
Ampicillin, agai,n the correct route because it's IV/IM.
What we want to do again is we want to learn this group of drugs,
how they're related; I put them all here for a reason
because they do have significant relationships to each other.
Let's change the question, practice question three, to make B) correct, so now we have to make amoxicillin right.
'A discharged patient requires an enteral, so a PO,
broad-spectrum penicillin antibiotic, which do you choose?
Well, ampicillin is an enteral broad-spectrum penicillin antibiotic,
but if we're thinking of the IV/IM, it's not the correct route,
but we also wouldn't have picked the oral dosage because it has
significantly more GI side effects, and you have QID dosing so
that literally means four times a day.
Amoxicillin has fewer Gi side effects,
and you can dose amoxicillin twice a day
but think of a bicycle with two tires or TID and think tri like tricycle with three tires.
BID, TID dosing, more likely the patient is going to get all the doses,
fewer GI effects and especially since we use this in children so much we don't want to have diarrhea and things like that that would
dehydrate them.
C) is amoxicillin with clavulanate
It's unnecessary to go to this drug. Clavulanate tends to cause
significant GI distress, and we don't have to go there yet because right now we
haven't tried to see if this is penicillinace resistant, and so this is going to have more GI effects.
It's unnecessary to bring out the big guns here. Cefdinir, if we were looking for a broad-spectrum penicillin,
cefdinir because the 'cef-' stem, we see it's not a penicillin.
Let's make C) correct.
A discharged patient tried an enteral broad-spectrum penicillin antibiotic which failed. Which penicillin do you choose now?'
This is an easy one because my daughter actually had this happen where she had tonsillectomy and adenoidectomy. She had tonsils and adenoids taken out.
She was put on amoxicillin for a week and
she complained of a double ear infection at day seven of amoxicillin,
so we take her in and
they evaluated her and see that she's got double ear infection, let's give amoxicillin. I say well
she's already on it, so we already knew that
the
bacteria had an enzyme to destroy the amoxicillin. Now which one do we use?
We asked for an enteral broad-spectrum penicillin antibiotics, so we're still not going to use this cefdinir, that's not a penicillin.
The ampicillin if we're thinking IV IM
it's not the correct route, but beta lactamase would also destroy that.
Amoxicillin,
beta lactamase will destroy that so that's not going to help us now.
We have amoxicillin with the clavulanate bodyguard and
this again is Augmentin - it augments the ability of amoxicillin by itself and
clavulanate imparts beta lactamase resistance to the amoxicillin and allows it to do its thing. Sure enough,
after she had the Augmentin for I think it was a week, then she was better and her ear infection went away.
Going along with that same story, a
discharged patient
tried an enteral broad-spectrum penicillin antibiotic which failed and previously clavulanate caused
unacceptable GI effects, which do you choose now?
The GI effects from clavulanate were so bad we,
struggled through to get her through that
medication that we wanted now a different choice that still had that beta lactamase resistance,
but now we use the third-generation cephalosporin because it has less GI effects. Ampicillin
is not the correct route, but also
because we are dealing with this beta lactamase resistant bug, we can't use ampicillin.
We can't use amoxicillin either.
We could have used amoxicillin with clavulanate, but the GI distress is unacceptable so now it's time for cefdinir, a third-generation
Cephalosporin that's Beta lactamase resistant, and then that's how we make D) correct.