INDICES> Guidelines for penicillin hypersensitivity testing? (2)

["Kirsten Myhr" <kirsten.myhr@relis.ulleval.no>]

INDICES> Guidelines for penicillin hypersensitivity testing? (2)
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Penicillin allergy has been discussed in Drug and Therapeutics Bulletin
1996; 34: 87-88 (November). I can fax you the pages if you give me a fax
number. The conclusion says:

''Allergy to penicillin is common, unpredictable and sometimes troublesome.
To minimise the problem, patients should only be prescribed a penicillin if
it is clearly indicated. If symptoms of hypersensitivity develop, this
should be recorded and every attempt made to assess whether they are due to
the drug or have occurred by chace. Before prescribing a penicillin, a drug
history should be taken. If there is convincing evidence of a previous
reaction, the drug is best avoided. If the history is unconvincing, a
penicillin can still be given, but the patient should be warned of the
potential risk and be closely monitored for the first 4 hours after
administration. Cross-sensitivity between penicillins and other beta-lactam
antibiotics varies. There seems to be little risk with aztreonam, while
cephalosporins and meropenem should only be used with extreme caution, and
imipenem avoided altogether [not everybody agrees on that. KM] . Skin tests
are an inaccurate way of diagnosing penicillin hypersensitivity and are not
without risk. ''Desensitisation'' is rarely justified.''
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BNF September 2001
The most important side-effect of the penicillins is hypersensitivity which
causes rashes and anaphylaxis, which can be fatal. Individuals who have
experienced anaphylaxis, urticaria, or rash immediately after penicillin
administration are at increased risk of immediate hypersensitivity to
penicillin; these individuals should not receive a beta-lactam antibiotic.
Patients who are allergic to one penicillin will be allergic to all because
the hypersensitivity is related to the basic penicillin structure.
Individuals who develop a minor rash or a rash that occurs more than 72
hours after penicillin administration are probably not allergic to
penicillin and in these individuals a penicillin should not be withheld
unnecessarily for serious infections; the possibility of an allergic
reaction should, however, be borne in mind.

Allergy to penicillin is seen in 1-10 % of patients. However,
life-threatening reactions are rare, anaphylactic reactions are seen in
15-40 per 100 000 users and is fatal in only 1.5-2 per 100 000.

The principal side-effect of the cephalosporins is hypersensitivity and
about 10% of penicillin-sensitive patients will also be allergic to the
cephalosporins.

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Here is a translation of the Norwegian guidelines (and we use lots of
penicillins!):

The reactions cans be divided in:
Acute reactions or early reactions. They happen within few minutes after
parenteral administration and within one hour after oral administration.
Type 1 reactions may, however, also occur after a few days of treatment
when
penicillin is used for the first time. This is an IgE mediated reaction and
is the ''true'' penicillin allergy. It is very rare (0,002%), but serious
and potentially fatal.

Late reactions occur more often and after more/many days of treatment as a
rash, fever etc. This is a cell-mediated allergic reaction and of limited
duration.

IgE mediated penicillin allergy can be determined by skin test, intradermal
test and RAST. Testing must take place in a specialist unit where
facilities
for constant monitoring and resuscitation are available. A negative test
may
help identify patients not in the risk group for a type 1 reaction and who
therefore may be given penicillin. There are however, false positives. The
value of a positive test is limited as up to 90% of the positives will
tolerate penicillin. The test does not seem to be able to predict which
patients will react to cephalosporins. Intradermal test and RAST are even
less reliable.

Desensibilisation is potentially life threatening and can rarely be
defended
as in most cases there will be an alternative antibiotic available.

We estimate cross-sensitivity to cephalosporins to be 3-7 % in patients
with
type ! reaction to penicillin.

Kirsten Myhr, MScPharm, MPH
Head of Eastern Region Drug Information Centre

RELIS Ost
Ulleval University Hospital
N-0407 OSLO
Tel: +47 23 01 64 11  Fax: +47 23 01 64 10
kirsten.myhr@relis.ulleval.no
www.relis.no

[Thanks, Kirsten, for this review! WB]


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