Charlotte Devantier Jensen.pmd - Videncenter for Allergi

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Contact allergy to the preservative methyldibromoglutaronitrile 11
MDBGN PATCH TEST CONCENTRATION AND VEHICLE
An important diagnostic tool for allergic contact dermatitis is
the epicutaneous patch test. Eczema patients are exposed to
common and suspected allergens under controlled conditions
and the skin response to the allergens is registered. To get reliable
readings, it is important to expose the patients to concentrations
of allergen that do not miss clinically relevant allergies
and will not frequently produce false-positive irritant reactions.
A commonly used MDBGN patch test concentration
is 0.3% in petrolatum (pet). In recent experiments, however,
the patch test concentration appears to miss clinically relevant
cases of contact allergy (personal communication). The higher
concentration of 0.5% MDBGN, though, often produces falsepositive
irritant reactions, which means that some patients will
be falsely diagnosed with contact allergy. But because of the
risk of false-negative reactions it is being considered to recommend
the use of a patch test concentration of 0.5% MDBGN
in pet.
EXPERIMENT EXAMINING THE MDBGN PATCH
TEST VEHICLE
The preferred MDBGN patch test vehicle is pet. Pet. is popular
as vehicle because of its ability to provide efficient occlusion,
keep allergens stable and, moreover, it is easy to work
with. It is, however, difficult to dose pet. accurately and therefore
it was decided to use an ethanol/water (eth./aq.) mixture
as vehicle in the experiments of this thesis. Ethanol was added
to ensure that the MDBGN was properly dissolved, as its solubility
in water is limited.
Fig. 4. Patch test reactions of
19 consecutive patients to
MDBGN in pet. and eth./aq.
Some patients had reactions to
several of or all test solutions.
Number of reactions
To examine and compare the patch test response to MDBGN
in eth./aq. and MDBGN in pet., a small experiment was performed.
20 consecutive patients were patch tested with
MDBGN in 3 concentrations: 0.1%, 0.3% and 0.5% in both
pet. and a 50:50 mixture of eth./aq. The patch test results are
presented in Fig. 4. 19 of the tested patients had a patch test
response on D3 to at least one of the patches with at least one
doubtful, positive or irritative reaction. The test size is limited,
but some tendencies were observed: a) MDBGN in eth./aq.
caused significantly more visibly irritative reactions than
MDBGN in pet. at the concentrations of 0.3% and 0.5%. Frequent
irritative reactions from Euxyl K 400 in ethanol have
been reported earlier 37 . b) With eth./aq. as vehicle, 3 patients
had a positive reaction (+) to at least one of the patch test concentrations
compared to 1 person with pet. as vehicle. c) Doubtful
reactions were frequent for all patches except 0.1% pet.
Most of these reactions are probably weak irritative reactions.
In general, stronger patch test responses with frequent irritative
reactions were seen to MDBGN in eth./aq. than to
MDBGN in pet. This was supported by patch test results from
Trial I of this project. The patients in Trial I were patch tested
with a dilution series of MDBGN (0.2%–0.001%) in eth./aq.
(50:50) along with a patch of 0.3% MDBGN pet. to compare
the patch test responses. (The highest concentration chosen in
the dilution series was 0.2% MDBGN eth./aq. to avoid most
irritative reactions). 0.2% MDBGN eth./aq. generally produced
a patch test response equal to or stronger than 0.3% MDBGN
pet. (Table 3). Feasible explanations for the augmented response
with the eth./aq. vehicle are a greater penetration of
0.1% 0.3% 0.5% 0.1% 0.3% 0.5%
Ethanol/aq Petrolatum
Irritative
Positive
Doubtful
Forum for Nord Derm Ven Vol. 10, 2005 – Suppl. 8