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Effects of topical petrolatum and salicylic acid upon skin photoreaction to UVA

European Journal of Dermatology. Volume 15, Number 3, 156-8, May-June 2005, Investigative report

Summary

Author(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.

Summary : Various agents which can be used in combination can also interfere with phototherapy. In this study, the effects of topical petrolatum and 20% salicylic acid in petrolatum upon skin photoreaction to UVA were investigated, in an in vivo test. Minimal phototoxic dose (MPD) test was performed on 31 volunteers and the test was repeated with thin (0.1 cc/25 cm ²) petrolatum, thick (0.3 cc/25 cm ²) petrolatum, thin 20% salicylic acid in petrolatum, thick 20% salicylic acid in petrolatum and sunscreen. The effect of each agent on MPD was investigated. MPD was increased with thin and thick applications of all agents. Also, MPD was increased with 20% salicylic acid in petrolatum when compared with pure petrolatum, in the same thickness. The application of petrolatum and salicylic acid in petrolatum just before PUVA therapy is not recommended because of their blocking effects.

Keywords : petrolatum, salicylic acid, UVA

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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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