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Dermal absorption

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Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
begin: 2005-09-05; end: 2006-01-11
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study was generated according to generally valid and accepted testing guidelines and performed according to GLP.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2006

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
Qualifier:
according to
Guideline:
other: OECD Environmental Health and Safety Publications Series on Testing and Assessment No.28. Guidance Document for the Conduct of Skin Absorption Studies
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): diantimony trioxide
- Analytical purity: 99.93%
- Lot/batch No.: 29113
- Storage condition of test material: ambient temperature in the dark
Radiolabelling:
no

Test animals

Species:
human

Administration / exposure

Type of coverage:
open
Vehicle:
other: Hydroxypropyl methylcellulose in water (1%, w/v)
Doses:
The resultant application rates of Diantimony Trioxide were, by mass, 95.27 μg/cm², 286.51 μg/cm² and 0 μg/cm².
Details on study design:
TEST SITE
- Preparation of test site:
Test Preparation 1:
Diantimony trioxide (19.05 mg) was transferred into a scintillation vial. Hydroxypropylmethylcellulose in water (1%, w/v) solution (19.13201 g) was
added to the diantimony trioxide. The sample was sonicated for ca. 3 minutes then placed onto a magnetic stirring plate for ca. 30 minutes to
generate a diantimony trioxide suspension. By weight, the concentration of diantimony trioxide in the test preparation was 0.99 mg/g, this is 99.47% of target 1 mg/g.

Test Preparation 2:
Diantimony trioxide (50.38 mg) was transferred into a scintillation vial. Hydroxypropylmethylcellulose in water (1%, w/v) solution (4.99249 g) was
added to the diantimony trioxide. The sample was sonicated for ca. 7 minutes then placed onto a magnetic stirring plate for ca. 5 minutes to
generate a diantimony trioxide suspension. By weight, the concentration of diantimony trioxide in the test preparation was 9.99 mg/g, this is 99.90% of target 10 mg/g.

Test Preparation 3 (control):
A solution of only hydroxypropyl methylcellulose in water was used as a control blank in all experiments to assess the background and endogenous
levels of antimony trioxide in the test samples.

Test Preparation 4:
Diantimony trioxide (986.83 mg) was transferred into a scintillation vial. Hydroxypropylmethylcellulose in water (1%, w/v) solution (9.77553 g) was
added to the diantimony trioxide. The sample was sonicated for ca. 3 minutes then placed onto a magnetic stirring plate for ca. 30 minutes to
generate a diantimony trioxide suspension. By weight, the concentration of diantimony trioxide in the test preparation was 91.69 mg/g, this is 91.69% of target 100 mg/g.

Test Preparation 5:
Diantimony trioxide (305.42 mg) was transferred into a scintillation vial. Hydroxypropylmethylcellulose in water (1%, w/v) solution (9.73822 g) was
added to the diantimony trioxide. The sample was placed onto a magnetic stirring plate for ca. 90 minutes to generate a diantimony trioxide
suspension. By weight, the concentration of diantimony trioxide in the test preparation was 30.41 mg/g, this is 101.36% of target 30 mg/g.

Test Preparation 6:
Diantimony trioxide (509.51 mg) was transferred into a scintillation vial. Hydroxypropylmethylcellulose in water (1%, w/v) solution (9.73702 g) was
added to the diantimony trioxide. The sample was placed onto a magnetic stirring plate for ca. 90 minutes to generate a diantimony trioxide
suspension. By weight, the concentration of diantimony trioxide in the test preparation was 49.73 mg/g, this is 99.45% of target 50 mg/g.

- no other details on study design reported
Details on in vitro test system (if applicable):
SKIN PREPARATION
- Source of skin: Ten samples of full-thickness human skin were obtained from patients. Nine of the samples were obtained from patients attending
the Plastic Surgery Unit, St Johns Hospital, West Lothian NHS Trust, Livingston, UK
- Ethical approval if human skin: The patients gave informed consent for their skin to be taken for scientific purposes.
- Type of skin: 3 abdomen and 7 breast
- Preparative technique: The skin was cleaned of subcutaneous fat and connective tissue using a scalpel blade. The skins were washed in cold running water and dried. When required, the human skin samples were removed from ca-20°C storage and allowed to thaw at ambient temperature.
Split-thickness membranes were prepared by pinning the full-thickness skin, stratum corneum uppermost, onto a raised cork board and cutting at a setting equivalent to 200-400 μm depth using a Zimmer electric dermatome.
Split-thickness skin membranes were divided into 36 pieces (ca 1.5 x 1.5 cm). The stratum corneum was removed from each skin sample by tape stripping with 20 successive tape strips. The skin samples were then placed into labelled vials (Skin 1-36). The corresponding tape strips were transferred into labelled vials (TS 1-36). Each sample was weighed to determine a sample weight. An additional four blank tape strip samples were also prepared.

- Thickness of skin (in mm): The thickness of the uncut skin membranes was measured using a micrometer.

- Storage conditions: The skin was transferred to Charles River Laboratories on ice. The sample was cut into smaller pieces (where appropriate),
wrapped in aluminium foil, put into self sealing plastic bags and stored at ca -20°C until required.
One of the skin samples (donor 0115) was obtained from Transkin under similar conditions as above. This was transferred to Charles River
Laboratories on dry ice and stored at ca -20 °C on arrival.
- Justification of species, anatomical site and preparative technique:

- no other details on in vitro test system reported

Results and discussion

Absorption in different matrices:
Based on the occurrence of antimony levels in skin as “natural background”, the corrected percutaneous absorption rates obtained in this study are as follows:
(i) total absorbed dose (amount penetrating to receptor medium) at 24h p.a. was 0.01% (at 100 ug/cm2 application rate) and 0.02% of dose (at 1,000 ug/cm2), respectively.
(ii) dermal delivery (i.e, total absorbed dose plus amount retained in or on skin after exposure/washing) at 24h amounted to 0.07% (at 100 ug/cm2 application rate) and 0.10% of dose (at 1,000 ug/cm2), respectively.
Overall, the percutaneous absorption of antimony trioxide through human skin is very low to negligible.

Any other information on results incl. tables

Analysed Results:

The data is presented as measured and following subtraction of the mean results obtained from the samples dosed with test preparation 3. For simplicity, the following results and discussion were based on the calculated data following subtraction of vehicle blank samples only.

Test Preparation 3:

A total of 6 samples of human skin, obtained from 4 different donors, were dosed topically with test preparation 3 (vehicle blank).

The mass balance, dislodgeable, unabsorbed, dermal delivery and absorbed doses were 0.47, 0.37, 0.39, 0.08 and 0.06 ¼g/cm2, respectively.

Table 3: distribution of diantimony trioxide (µg/cm*3) at 24 hours post dose following topical application of test preparation 3 to human split-thickness skin.

cell and donor No.

cell 42

0125

cell 45

0115

cell 51

0121

cell 55

0125

cell 63

0121

cell 65

0112

mean

SD

skin wash

0.19

0.19

0.19

0.19

0.19

0.19

0.19

0.00

tissue swab

0.19

0.19

0.19

0.19

0.19

0.19

0.19

0.00

dislodgeable dose

0.37

0.37

0.37

0.37

0.37

0.37

0.37

0.00

stratum corneum

0.02

0.02

0.02

0.02.

0.02

0.02

0.02

0.00

total unabsorbed

0.39

0.39

0.39

0.39

0.39

0.39

0.39

0.00

exposed skin

0.02

0.02

0.02

0.02

0.02

0.02

0.02

0.00

receptor fluid

0.04

0.08

0.06

0.07

0.07

0.06

0.06

0.01

absorbed dose

0.04

0.08

0.06

0.07

0.07

0.06

0.06

0.01

dermal delivery

0.06

0.09

0.07

0.09

0.09

0.08

0.08

0.01

mass balance

0.45

0.49

0.47

0.48

0.48

0.47

0.47

0.01

Dislodgeable dose = skin wash + tissue swab

Total unabsorded = dislodgeable dose + stratum corneum

Absorbed dose = receptor fluid

Dermal delivery = absorbed dose + exposed skin

The values obtained for test preparation 3 were subtracted from test preparations 2 and 5 as background values.

The receptor fluid samples also included the subtraction of the predose samples as the background values.

Test Preparation 2:

A total of 6 samples of human skin, obtained from 4 different donors, were dosed topically with test preparation 2, diantimony trioxide in hydroxypropyl methylcellulose at a nominal concentration of 10 mg/ml.

The mass balance, dislodgeable, unabsorbed, dermal delivery and absorbed doses were 72.23, 71.89 72.17, 0.06 and 0.01 ¼g/cm2, respectively. The mean mass balance was 89.77% of the applied dose.

At 6 hours post dose, 89.35% of the applied dose was washed off (32.52% recovered in the 6 hours skin wash and 56.83% recovered in the 6 hours tissue swab). Therefore the dislodgeable dose is 89.35% of the applied dose. At 24 hours post dose, ie after an 18 h monitoring period, the mean total unabsorbed dose was 89.70% of the applied dose. This consisted of the dislodgeable dose, and the diantimony trioxide associated with the stratum corneum (0.34%). The absorbed dose (0.01%) was the cumulative sum of the diantimony trioxide detected in the receptor fluid samples. Dermal delivery (0.07%) was the sum of the absorbed dose and the exposed skin (0.07%).

Test Preparation 5:

A total of 6 samples of human skin, obtained from 4 different donors, were dosed topically with test preparation 5, diantimony trioxide in Hydroxypropyl methylcellulose at a nominal concentration of 30 mg/ml. The mass balance, dislodgeable, unabsorbed, dermal delivery and absorbed doses were 242.47, 242.07, 242.24, 0.24 and 0.05 ¼g/cm2, respectively. The mean mass balance was 106.41% of the applied dose. At 6 hours post dose, 106.23% of the applied dose was washed off (12.06% recovered in the 6 hours skin wash and 94.18% recovered in the 6 hours tissue swab). Therefore the dislodgeable dose is 106.23% of the applied dose. At 24 hours post dose, ie after an 18 h monitoring period, the mean total unabsorbed dose was 106.31% of the applied dose. This consisted of the dislodgeable dose, and the diantimony trioxide associated with the stratum corneum (0.07%). The absorbed dose (0.02%) was the cumulative sum of the diantimony trioxide detected in the receptor fluid samples. Dermal delivery (0.10%) was the sum of the absorbed dose and the exposed skin (0.08%).

Normalised Results

The results presented above were then normalised based on the mass balance for each individual sample normalised to 100%.

Test Preparation 2:

At 6 hours post dose, 99.56% of the applied dose was washed off (35.73% recovered in the 6 hours skin wash and 63.83% recovered in the 6 hours tissue swab). Therefore the dislodgeable dose is 99.56% of the applied dose. At 24 hours post dose, ie after an 18 hours monitoring period, the mean total unabsorbed dose was 99.94% of the applied dose. This consisted of the dislodgeable dose, and the diantimony trioxide associated with the stratum corneum (0.38%). The absorbed dose (0.01%) was the cumulative sum of the diantimony trioxide detected in the receptor fluid samples. Dermal delivery (0.06%) was the sum of the absorbed dose and the exposed skin (0.05%).

Test Preparation 5:

At 6 hours post dose, 99.82% of the applied dose was washed off (11.60% recovered in the 6 hours skin wash and 88.22% recovered in the 6 hours tissue swab). Therefore the dislodgeable dose is 99.82% of the applied dose. At 24 hours post dose, ie after an 18 hours monitoring period, the mean total unabsorbed dose was 99.90% of the applied dose. This consisted of the dislodgeable dose, and the diantimony trioxide associated with the stratum corneum (0.07%). The absorbed dose (0.02%) was the cumulative sum of the diantimony trioxide detected in the receptor fluid samples. Dermal delivery (0.10%) was the sum of the absorbed dose and the exposed skin (0.08%).

Applicant's summary and conclusion

Conclusions:
Under the present testing conditions the total dermal absorption is estimated to 0.26 % (0.07 + 0.38/2) and 0.135 % (0.1 + 0.07/2) respectively, for the two tested low and high dose., Therefore, based on this study a value of 0.26% for dermal absorption is suggested. This calculated value is low. Still, the donor specific dermal absorption in the corrected vs. the non-corrected exposure groups is significantly different (Wilcoxon-signed rank test, p < 0.01). The large standard deviation in exposed samples in this test may be explained by the limited number of samples with possibly intra and inter individual differences.
In conclusion, even though the donor specific dermal absorption in the corrected vs. the non-corrected combined exposure groups is significantly different, the dermal absorbtion of 0.26% is still low, and dermal absorption of diantimony trioxide is considered negligible.