Sodium dibutyldithiocarbamate

Dermal absorption

Administrative data

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Read-across to GLP, guideline study

Justification for type of information:

The endpoint for repeated dose toxicity of SDBC is based on read-across to its structural homologue sodium diethyldithiocarbamide (SDEC). SDBC and SDEC are structural homologues of each other with the same sodium dithiocarbamate backbone, differing only in the length of alkyl substituents at the amine function of the dithiocarbamate moieties (ethyl for SDEC vs butyl for SDBC, respectively). The read-across justification is attached to Section 13.

Cross-reference

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Remarks:

14C

Type of coverage:

other: open (experiment 1) and semi-occlusive (experiment 2)

Vehicle:

water

Duration of exposure:

8 hours with 16 hours post-exposure

Doses:

2433 ± 27 and 236 ± 3 µg x cm-2 in experiment 1 (doses A and B, 23.4% and 2.34% solutions of SDEC)
2469 ± 16 µg x cm-2 in experiment 2 (23.4% solution of SDEC)

Details on study design:

DOSE PREPARATION
- Method for preparation of dose suspensions: For dose preparation A, the proper amount of [14C]SDEC dissolved in an adequate solvent, was transferred to a vial and the solvent was evaporated under N2 gas until dryness. Subsequently, the proper amount of Perkacit SDEC liq-w26% formulation was added and mixed.

For dose preparation B, the proper amount of [14C]SDEC, was transferred to a vial and the solvent evaporated under N2 gas until dryness. The proper amount of Perkacit SDEC liq-w26% formulation, 1:10 diluted with demineralised water, was added and mixed.

- Method of storage: The dose preparations were kept at ambient temperature until application.

APPLICATION OF DOSE: The dose preparations were applied with a pipette tip and spread evenly on the skin surface within the donor compartment (10 µL.cm-2). The dose preparations were carefully mixed before each administration. The concentration and homogeneity of [14C]SDEC in the dose preparations were checked by taking aliquots just before and directly after dosing. The aliquots are divided in the net dose applied and the amount of radioactivity remaining in the pipette tip, while their sum is considered the gross dose used to determine the concentration and homogeneity. The coefficient of variation (CV) was found to be lower than 10 % (i.e. 0.8 % (A), 1.0 % (B) and 2.0 %, and therefore considered sufficient. The radiochemical purity of [14C]SDEC in the dose preparations was found to be > 98 %


TEST SITE
- Area of exposure: a net volume of approximately 6.4 µL of the dose preparations was applied on each skin membrane (0.64 cm2).

REMOVAL OF TEST SUBSTANCE
- Washing procedures and type of cleansing agent: After an exposure period the unabsorbed test substance was removed from the application site using a mild soap solution (i.e. a 3 % Teepol in water) and cotton swabs.
- Time after start of exposure: 8 h


ANALYSIS
- Method type for identification: liquid scintillation counting

Details on in vitro test system (if applicable):

SKIN PREPARATION
- Source of skin: human skin from three donors, obtained directly after surgery
- Ethical approval if human skin: yes
- Type of skin: derived from abdomen and/or breast
- Preparative technique: thawn from frozen skin samples. Subcutaneous fat was removed and the skin was stored in aluminium foil at < −18 °C until use. The skin of donor 1 was stored overnight at 2 – 10 °C before subcutaneous fat was removed.
- Thickness of skin (in mm): ca 400 µm
- Membrane integrity check: yes
- Storage conditions: frozen

PRINCIPLES OF ASSAY
- Diffusion cell: 9 mm flow-through automated diffusion cells (PermeGear Inc., Riegelsville, PA, USA).
- Receptor fluid: phosphate buffered saline (PBS).
- Solubility of test substance in receptor fluid: freely soluble
- Flow-through system: yes
- Test temperature: 32 ± 1 ºC
- Humidity: ambient
- Occlusion: no
- Reference substance(s): [3H]H2O

Total recovery:

- Total recovery: The mean recovery of [14C]SDEC in human skin in the first experiment was 83.4 ± 3.1 % and 49.5 ± 5.3 % for the undiluted (experiment A) and 1:10 dilution (experiment B) solution, respectively.
An additional study was performed to try to explain the low recoveries that were found.
As a result from the eight hour exposure of the test solution to a temperature >30 °C, volatiles may have been formed. Therefore, dermal absorption of SDEC from the undiluted Perkacit SDEC liq-w26% was tested again while the donor compartment was kept semi-occluded by a charcoal filter. Furthermore, NaOH was added to increase pH and stabilize the test compound in the various fractions and prevent the possible formation of insoluble complexes.

The (semi-) occlusive conditions result in an increase in dermal absorption which was expected as occlusive conditions are known to enhance dermal absorption. The mean absorption of [14C]SDEC from the undiluted Perkacit SDEC liq-w26% formulation into the receptor fluid under semi-occlusive conditions increased to 170.14 µg.cm-2 after 24 hours, representing 6.89 % of the dose applied. The mean maximal flux increased to 36.63 µg x cm-2 x h-1. The lag time was comparable, i.e. 5.1 h.

The mean total absorption was 7.48 % of the dose applied and the mean total recovery improved to 92.9 ± 4.2 %.

Dose:

2469 ± 16.01

Parameter:

percentage

Absorption:

7.48 %

Remarks on result:

other: 8 hr

Remarks:

semi-occlusive conditions

In the first experiment, the mean absorption of [¹⁴C]SDEC from an undiluted Perkacit SDEC liq-w26% formulation into the receptor fluid after 24 hours was 92.34 µg.cm^-2, representing 3.77 % of the dose applied. The mean maximal flux for the absorption of SDEC through human skin was 27.13 µg.cm^-2.h^-1. The lag time was 4.5 h.

The mean absorption of [¹⁴C]SDEC from a 10-times diluted Perkacit SDEC liq-w26% formulation into the receptor fluid after 24 hours was 2.21 µg.cm^-2, representing 0.94 % of the dose applied. The mean maximal flux for the absorption of SDEC through human skin was 0.31 µg.cm^-2h^-1. The lag time was 2.7 h. For the 10-times diluted Perkacit solution, a clear difference in dermal absorption between donors was observed.

The mean total absorption, defined as the compound-related radioactivity present in the receptor fluid, the receptor compartment wash and the skin membranes but excluding the tape strips was 4.13 % (undiluted Perkacit) and 1.49 % (10-times diluted Perkacit) of the dose applied.

 The mean recovery of [¹⁴C]SDEC in human skin was 83.4 ± 3.1 % and 49.5 ± 5.3 % for the undiluted and 1:10 dilution solution, respectively.

 

In the second experiment, performed under semi-occlusive conditions, negligible amounts were recovered from the charcoal filter. The formation of volatiles therefore does not explain the low recoveries in the first experiment. A substantial increase in recovery resulted from the change in extraction procedure for the cotton swabs, using 0.1 M NaOH in water. It appears that the dermal absorption data obtained in experiment 1 are therefore reliable and that the missing radio-activity which caused the low recoveries values should be contributed to the skin wash (i.e. the cotton swabs).

 

It should be noted that, most likely as a result from the high pH of the Perkacit formulation, both the undiluted and diluted solutions appeared to have interfered with the integrity of the stratum corneum and, consequently, its barrier properties. This effect was confirmed by the fact that tape stripping was very difficult and is illustrated by the increasing relative absorption with increasing dose levels; in general, relative absorption decreases with increasing dose levels.

Materials and methods

Test material

Test material information

Constituent 1

Reference substance name:

Sodium dibutyldithiocarbamate

EC Number:

205-238-0

EC Name:

Sodium dibutyldithiocarbamate

Cas Number:

136-30-1

Molecular formula:

C9H19NS2.Na

IUPAC Name:

sodium (dibutylcarbamothioyl)sulfanide

Details on test material:

- Name of test material (as cited in study report): Sodium dibutyldithiocarbamate (perkacit SDBC liq-w47%)
- Physical state: clear light yellow liquid
- Analytical purity: 46.20% (concentrated aqueous solution)
- Expiration date of the lot/batch: 19 April 2011 (allocated by NOTOX, 1 year after receipt of the test substance)
- Stability under test conditions: stable
- Storage condition of test material: at room temperature in the dark under nitrogen

Results and discussion

Percutaneous absorption

Absorption:

7.48 %