ARTICLE
Auteur(s) :, Bahar Birgin, Emel Fetil*, Turna
Ilknur, Ali Tahsin Güneş, Şebnem Özkan
Department of Dermatology, University of Dokuz Eylül, Faculty of
Medicine, 35340 İzmir, Turkey
accepté le 17 Decembre 2004
Successful treatment of psoriasis depends on an adequate
penetration of the ultraviolet radiation to the level of viable
epidermal cells. However, psoriasis scales act as a partial barrier
for ultraviolet radiation [1]. So, it is important to remove the
scales of psoriasis lesions. Salicylic acid is one of the most
effective and basic keratolytic agents. It is commonly used in
petrolatum for the lesions of psoriasis patients and has a
keratolytic effect in concentrations of 5% or above [2]. In this
study the effect of using salicylic acid in petrolatum, just prior
to UVA radiation was investigated.
Materials and method
The study was designed as a single-blind, vehicle-controlled study
to determine minimal phototoxic dose (MPD) after the application of
white petrolatum and 20% salicylic acid in white petrolatum. The
test was carried out on 31 volunteers with a diagnosis of
psoriasis, lichen planus, parapsoriasis and vitiligo before their
PUVA therapy. Two patients were skin type II, 27 patients were skin
type III, two patients were skin type IV. The study was approved by
an ethics committee. All participants were informed and consent
forms were obtained. The patients were untanned and not taking any
medication. Waldmann 8001 K (Waldmann Lichttecnik Gmbtt,
Schwenningen, Germany) cabin was used for the light source of UVA.
MPD test was performed on volunteers 2 hours after taking
0.6-0.8 mg/kg 8-methoxypsoralen (8-MOP). According to the skin
types of volunteers, the doses of UVA were determined. Patients
with skin types I and II were exposed to doses of 0.5-5
J/cm2 and patients with skin types III and IV were
exposed to doses of 1.5-9 J/cm2 of UVA [3]. MPD was
determined by irradiating 4 cm2 of uninvolved skin
on the back of each patient to 6 different areas for skin types I
and II and 9 different areas for skin types III and IV, in one row,
with increments of 1 J/cm2 (0.5 J/cm2 only
for the first one). In addition 5 parallel rows of skin were tested
after the application of different topical agents.
The first row was only irradiated by UVA without application of
any topical agent to determine MPD. Thin (0.1
cc/25 cm2) layer of white petrolatum, thick
(0.3 cc/25 cm2) layer of white petrolatum,
thin (0.1 cc/25 cm2) layer of salicylic acid (20%)
in white petrolatum, thick (0.3 cc/25 cm2) layer of
salicylic acid (20%) in white petrolatum and sunscreen factor 15
(titanium dioxide + octyl methoxy cinnamate) were applied
respectively to the adjacent parallel rows and irradiated with UVA,
just after the application of the agents.
The results were evaluated after 72 hours by a blinded
investigator and MPD values were determined for each row ( (figure 1) ).
Paired-Samples T test was used for the statistical analysis of the
test results. Bonferroni-corrected significance level p <
0.00625 was considered statistically significant.
Results
The results of the MPD tests of all patients with pure PUVA, with
the application of a thin layer of petrolatum, a thick layer of
petrolatum, a thin layer of salicylic acid (20%) in petrolatum and
a thick layer of salicylic acid (20%) in petrolatum are shown in
table 1( Table 1 ). Sunscreen caused
total blocking on all the subjects.
MPD values detected after pure PUVA were compared, one by one,
with MPD values detected after the application of topical agents
and all of them were found statistically significant
(Paired-Samples T test p < 0.00625). These findings showed that
MPD values were increased by thin or thick application of
petrolatum and also by thin or thick application of salicylic acid
(20%) in petrolatum. However, a statistically significant
difference between the MPD values of thin and thick application of
petrolatum and also between the MPD values of thin and thick
application of salicylic acid (20%) in petrolatum were not
determined (Paired-Samples T test, p > 0.00625).
There was a statistically significant difference between the MPD
values of thin application groups (thin petrolatum and thin
salicylic acid in petrolatum) and between the MPD values of thick
application groups (thick petrolatum and thick salicylic acid in
petrolatum), (Paired-Samples T test, p < 0.00625). Thin
application of salicylic acid in petrolatum resulted in an increase
of MPD values when compared with the thin application of petrolatum
and also the thick application of salicylic acid in petrolatum
resulted in an increase of MPD values when compared with the thick
application of petrolatum. The results of the Paired-Samples T test
of all the paired groups are shown in table 2( Table 2 ).
Table 1 MPDs of volunteers (n = 31)
|
Preparation
|
MPD (J/cm2)
|
|
Mean ± SD
|
|
UVA without any agent
|
2.26 ± 1.30
|
|
Thin petrolatum
|
2.74 ± 1.47
|
|
Thick petrolatum
|
2.95 ± 1.50
|
|
Thin salicylic acid (20%) in petrolatum
|
3.29 ± 1.55
|
|
Thick salicylic acid (20%) in petrolatum
|
3.61 ± 1.70
|
Table 2 Paired-Samples T test
|
Paired groups
|
Mean ± SD
|
t
|
Significance
|
|
UVA-P
|
–0.48 ± 0.92
|
–2.94
|
0.006
|
|
UVA-TP
|
–0.69 ± 1.01
|
–3.84
|
0.001
|
|
UVA-S
|
–1.03 ± 1.16
|
–4.95
|
0.000
|
|
UVA-TS
|
–1.35 ± 1.42
|
–5.33
|
0.000
|
|
P-TP
|
–0.21 ± 0.50
|
–2.35
|
0.025
|
|
S-TS
|
–0.32 ± 0.67
|
–2.70
|
0.011
|
|
P-S
|
–0.55 ± 1.03
|
–2.97
|
0.006
|
|
TP-TS
|
–0.66 ± 1.14
|
–3.24
|
0.003
|
Discussion
Various agents can be used in combination and interfere with
phototherapy [4-7]. It has been shown that transmission of
radiation through psoriatic plaques was increased following the
application of lipophilic compounds. Conversely, photoprotective
effects of several emollients have been shown [1, 6, 7]. Sufficient
penetration of ultraviolet is important for the treatment of
psoriasis lesions [1, 4]. In a clinical study, Kristensen et al.
detected that salicylic acid application before UVB therapy can
decrease the improvement rate of psoriasis [6]. In psoriasis
patients, Berne et al. detected an acceleration in the improvement
rate on lesions treated with oil-in-water type emollient [8]. So,
several studies have been designed to show the enhancing or
blocking effects of topical agents on ultraviolet penetration [4,
6, 7, 9, 10].
It is important to know the effects of topical agents on UVB or
UVA penetration, especially the ones which are frequently used in
combination with phototherapy. So, at this point it is also
important to know the effects of salicylic acid preparations on UVB
or UVA penetration, because it is the most effective and basic
keratolytic agent used for psoriasis patients.
Kristensen et al. have shown in an in vitro study, that
salicylic acid in the interval of 295-323 nm and petrolatum below
295 nm, can absorb light at their highest degrees [6]. Likewise, in
an in vitro study Korneich et al. showed that 3% salicylic acid in
petrolatum had a high absorbance value for UVB (310 nm), but only
petrolatum had a low absorbance value [4]. However, in an in vitro
study Hoffman et al. found that petrolatum can enhance the
transmission of UVB [11].
Lebwohl et al. investigated the ability of topical preparations
to block UVB in an in vivo study. They found that 6% salicylic acid
ointment and thick (0.8 cc/24 cm2) petrolatum did
block UVB if not removed before therapy and they concluded that
these agents if applied before therapy can reduce the efficacy of
phototherapy for psoriasis [7]. Moreover, in an in-vivo study it
has been found that thin (0.1 cc/25 cm2) or thick
(0.3 cc/25 cm2) petrolatum and 20% salicylic acid
in petrolatum can block UVB and their blocking effects increased
parallel with their thickness [12]. However, in Lebwohl’s study,
the blocking effect was not detected with thin (0.4
cc/24 cm2) application of petrolatum [7].
Kristensen et al. studied the effect of salicylic acid on UVB
transmission in an in vivo study with the application of different
concentrations of salicylic acid (2, 5, 10%), and found that
salicylic acid had a dose-dependent blocking effect on UVB which
persisted for at least 12 hours and sometimes 24 hours [6].
There are not many studies which have been performed to
determine the effects of topical preparations on UVA penetration.
Korneich et al. in an in vitro study found that petrolatum and 3%
salicylic acid in petrolatum had a lower absorbance value in the
UVA (360 nm) range compared to the UVB (310 nm) range. Also, in the
UVA range, the absorbance value of petrolatum was detected to be
higher than 3% salicylic acid in petrolatum [4]. Conversely, in an
in vitro study Hoffmann et al. found that thin petrolatum can
enhance the transmission of UVA, however, a thick layer gave a
slight lowering of the transmission. Also, they concluded that
transmission in the UVB range was higher than in the UVA range
[11]. In an in vivo study Boyvat et al. found a slight decrease of
MPD for UVA after application of petrolatum and 3% salicylic acid
in petrolatum [9].
We observed in this study, blocking effects of white petrolatum
and 20% salicylic acid in petrolatum when applied immediately
before UVA. Our results, showing the blocking effects of these
substances are in accordance with Korneich’s results, however our
salicylic acid preparation is more concentrated and because of that
in our study the blocking effect of it has been found more than
pure petrolatum. Although we must use salicylic acid in petrolatum
to remove the scales of psoriasis lesions before photochemotherapy,
because of its blocking effect, we must not use it immediately
before UVA radiation.
References
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