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: Penicillin Allergy: Sometimes Confusing
DEAR DR.PAUL: My son had an allergic
reaction to amoxicillin. He has had a penicillin allergy test
that came back negative, however we read that it is possible to
be allergic to amoxicillin but not to penicillin. Is this a true
possibility?
DR.PAUL ANSWERS: Your question brings
up several important points about penicillin allergy. However,
let me take this opportunity to discuss antibiotic allergy in
general, as there can really be a lot of confusion around this
issue. Many parents seem to think that any reaction to an antibiotic
is allergic. However it is important to realize that there is
a difference between a true allergic reaction and a side effect
of the medication itself. Antibiotics, as all other medications,
have potential effects; both helpful ones like fighting off bacteria
and unwanted "side effects". We know that certain antibiotics
tend to cause more vomiting, abdominal discomfort and diarrhea
than others. So when a parent reports that a child has had such
symptoms, we recognize this is a side effect of the medication
and not an allergic reaction. This distinction is important as
we do not want to falsely label a child as being allergic to penicillin
when truly he or she is not.
An allergy develops when a person's body has a bad reaction to
a particular substance or product, such as penicillin. Allergic
reactions to medications usually have very specific symptoms including:
an itchy rash or urticaria, swelling of the throat/mouth area
and difficulty breathing. Also, very rarely, allergic reactions
to medications, including penicillin, can be potentially life
threatening. There are also different types of allergic reactions.
Some that occur right away and others that appear several days
after starting the antibiotic or even within a week after stopping
it. In any case, my point is that there is an important difference
between a side effect and an allergic reaction. How does one confirm
a penicillin allergy? By allergy (skin) testing to penicillin,
the only antibiotic we can actually test for. If a child tests
positive, then he or she is considered allergic to penicillin
and should not be given penicillin the future. If the test is
negative the child is not penicillin allergic.
Penicillin is a beta-lactam antibiotic while, amoxicillin is an
amino-penicillin. In other words, it is a modified form of penicillin.
It is a beta-lactam molecule with another(amino)molecule stuck
onto it. It is not uncommon for children to react to the amino
part of the amoxicillin molecule and not the penicillin (beta-lactam)
part. So these children, although have had a reaction to amoxicillin,
technically are not allergic to the penicillin molecule. They
had an allergic reaction to the "non-penicillin portion" of the
amoxicillin molecule. In this case, just like with your son, the
penicillin allergy test is negative. So in the future, penicillin
can be given to your son, but not amoxicillin.
On a final note, if there is a doubt about a penicillin allergy,
it should be verified one way or the other. This clarification
will be extremely helpful in deciding which antibiotic to use
in case a future need arises. |
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