Test Methods

Sufficiently large field studies proving the efficacy of BP products under real-life conditions are scarce. In fact, the only study that shows the efficacy of a product in this respect is a field study in kitchen workers and cleaners, which showed protective properties of the O/W fatty cream previously mentioned [19]. The availability of reliable laboratory test methods is, therefore, essential, both for classification of products and for the development of new products. Suitable tests should give quantitative read-outs, include appropriate standard preparations and controls, and mimic wear-and-tear conditions when applicable.

Hallmarks for tests with a good predictive clinical value in this respect are the use of low, subtoxic doses of the irritant and repetitive application for 1 to 2 weeks, in absence or presence of pretreatment with test products thus mimicking real-life conditions. If wash-off is important for the target user groups of certain products, modifications can be made, which include washing schemes. After pioneering work by Lachapelle and coworkers [20], Frosch and colleagues have validated a test schedule in human volunteers where pretreatment of the skin with BP products was followed by repetitive treatment with a panel of irritants consisting of diluted solutions of sodium lauryl sulphate, sodium hydroxide, lactic acid, and undiluted toluene [1]. Other groups have used similar approaches on the back or forearm of human volunteers [10,21,22].

In vitro tests for assessing the protective ability of topical products generally have a poor predictive value for the in vivo situation [23]. However, for candidate selection in large-scale industrial development programs, such tests are indispensable to cut time-consuming product-screening procedures. In this respect, a method to test the water-repellent properties of formulations applied on slides dipped into a 1% eosin solution and evaluated for the absorption of color with a chromameter was found valuable as a preselection tool in a development program to identify products against water-based irritants, whereas another test where penetrating dye was assessed after application of the products

on a filter paper was of very limited value in this respect (author: unpublished observations). Although some animal tests may be worthwhile because of an obvious good clinical predictability of the results, e.g., the repetitive irritation test in guinea pigs [12], similar information can be obtained in human volunteer studies, avoiding sacrifice of animals.

In an industrial program aimed to develop an O/W cream that should protect against water-based irritants, maintain activity after washing, and with acceptable cosmetic properties, we have used a series of in vitro and human volunteer tests in serial and parallel combination. The test sequence was composed of high-capacity (in vitro) tests as the first selectors, and more laborious tests later on. Firstly, the in vitro eosin dip test was used as mentioned above. Secondly, formulations were tested into an in vivo eosin penetration test (see Fig. 4) and a cosmetic properties test [24]. Formulations that complied with predefined activity and cosmetic standards were taken into a repetitive-irritation test with sodium lauryl sulphate (SLS). The protocol for this test was based on procedures as published by Frosch's group [1], but including a wash-off scheme and with SLS as the only irritant. Typical results for a test run with the eosin penetration test and the repetitive irritation test are given in Figures 4 and 5.

Figure 4 Results from a comparison of six experimental protective products (prepared by Yamanouchi Europe B.V., Leiderdorp, The Netherlands). (A, C, D, F, G, H) and two reference products (B, E) in an eosin dye penetration test with (first column) and without (second column) wash-off schedule. In eight healthy males, 50 |il of the test formulations was applied on 4 areas/arm of 4 X 5 cm. After rubbing in, the left sites of the spots were washed off gently with water. Accordingly, at all sites small paper disks, soaked in 1% eosin solution, were applied. After washing all sites, colorimetry (a* parameter) was performed with a Minolta CR300 colorimeter, and the difference with untreated was noted. (A low value for a* denotes good protective properties.) Preparations used: (A) 45% liquid paraffin/10% carnauba wax/ 3% glycerin W/O cream; (B) commercial hand cream including among others (a.o.) alcohols, waxes, paraffin, W/O and O/W emulsifiers, glycerin, dimethicone, and water;(C) 25% petroleum jelly in Carbopol 1382 O/W gel; (D) 10% ceresine wax added to an O /W fatty cream;

(E) commercial W/O ointment containing mineral oil, petrolatum, Eucoriol, lanolin, Ozokerite;

(F) 38% beeswax/34% Miglyol812 O/W oleogel;(G) 100% petroleum jelly;(H) 45% liquid paraffin/3% glycerin W/O cream.

Figure 5 Results from a comparison of three experimental protective products (prepared by Yamanouchi Europe B.V., Leiderdorp, The Netherlands) (A, C, D) with a reference product (B) in a repetitive irritation test after five treatment days with SLS and incubation time of 1 h (first bar), 3 h (second bar), and with wash-off treatment (third bar). In this test eight healthy males were treated on 12 spots on the back with rubbing in 50 |il of the four formulations, applied in each column. Each row was allocated to one of the schedules: 1 h incubation, 3 h incubation, or wash-off after 30 min, whereas at 1 h after application 50 |il patches filled with 10% SLS were applied for 30 min. Erythema was scored with a chromameter (Minolta CR300) using the a* scale. Visual damage was scored on a scale from 0-4 (Frosch PJ, Kligman AM. The soap chamber test. J Am Acad Dermatol 1979;1:35-41). The visual damage scores after five treatment days are given. Preparations used: (A) 4% perfluoroether (FomblinHC) added to an O/W fatty cream;(B) commercial W/O ointment containing a.o. mineral oil, petrolatum, Eucoriol lanolin, Ozokerite;(C) 4% FomblinHC/15% octyl, stearate W/O cream;(D) 4% FomblinHC/18% Miglyol812/15% propyleneglycol O/W cream.

Figure 5 Results from a comparison of three experimental protective products (prepared by Yamanouchi Europe B.V., Leiderdorp, The Netherlands) (A, C, D) with a reference product (B) in a repetitive irritation test after five treatment days with SLS and incubation time of 1 h (first bar), 3 h (second bar), and with wash-off treatment (third bar). In this test eight healthy males were treated on 12 spots on the back with rubbing in 50 |il of the four formulations, applied in each column. Each row was allocated to one of the schedules: 1 h incubation, 3 h incubation, or wash-off after 30 min, whereas at 1 h after application 50 |il patches filled with 10% SLS were applied for 30 min. Erythema was scored with a chromameter (Minolta CR300) using the a* scale. Visual damage was scored on a scale from 0-4 (Frosch PJ, Kligman AM. The soap chamber test. J Am Acad Dermatol 1979;1:35-41). The visual damage scores after five treatment days are given. Preparations used: (A) 4% perfluoroether (FomblinHC) added to an O/W fatty cream;(B) commercial W/O ointment containing a.o. mineral oil, petrolatum, Eucoriol lanolin, Ozokerite;(C) 4% FomblinHC/15% octyl, stearate W/O cream;(D) 4% FomblinHC/18% Miglyol812/15% propyleneglycol O/W cream.

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