Registration Dossier

Administrative data

Endpoint:
dermal absorption in vivo
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Comparable to guideline study; Critical study for SIDS endpoint. Read-across justification: The substance is hydrolytically unstable. When it comes in contact with water or moisture complete hydrolysis will take place with no significant reaction products other than alcohol and hydrated titanium dioxide. This rapid hydrolysis (hydrolysis half-life < 3 minutes to < 2 hours) is the driving force for the toxicokinetics of target substance. Because of the rapid hydrolysis, the influence of the mode of administration through inhalation, dermal and oral is related to the hazardous degradation product (alcohol) released from the target substance. The identification of degradation products from the hydrolysis study conducted for the target substance verifies that there are no impurities in the alcohol released from the target substance, which might change the hazardous properties of the target substance compared to the properties of the pure alcohol. As there is a mechanistic reasoning to the read-across, the unnecessary animal testing is avoided by using the read-across data from the degradation product (relevant alcohol) to evaluate irritation, sensitization and the short term and long-term toxicological effects and mutagenicity of the target substance.
Cross-reference
Reason / purpose:
reference to same study

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
1994
Report Date:
1994

Materials and methods

Principles of method if other than guideline:
AME (absorption, metabolism, excretion) following dermal application of [14C]-2-EH
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
cf. cross-referenced study
Radiolabelling:
yes

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
female
Details on test animals and environmental conditions:
cf. cross-referenced study

Administration / exposure

Type of coverage:
other: Pyrex glass cylinders
Vehicle:
unchanged (no vehicle)
Duration of exposure:
96 hours
Doses:
1 g/kg bw
Details on study design:


APPLICATION OF DOSE:



TEST SITE
- Preparation of test site: shaved dorsal skin
- Area of exposure: 2.27 mm² (inner diameter of the Pyrex glass cylinder)
- Type of cover / wrap if used: adhesive



SITE PROTECTION / USE OF RESTRAINERS FOR PREVENTING INGESTION: yes: adhesive


REMOVAL OF TEST SUBSTANCE
- Washing procedures and type of cleaning agent: aspiration of remaining test material, repeated washing with a 40% Hisoderm soap solution
- Time after start of exposure: 6 hrs


SAMPLE COLLECTION
- Collection of blood: from the tail vein; 5 samples within the first 10 min; then at 25, 50, 75, and 95 min.
- Collection of urine and faeces: separately, at intervals 0-8; 8-24; 24-48; 48-96 hrs
- Collection of expired air: (1) in sodium hydroxide traps and (2) in silica gel traps; time intervals as above
- Terminal procedure: no data
- Analysis of organs: no


SAMPLE PREPARATION
- Storage procedure: freezing until use (urine, faeces); blood: heparinised
- Preparation details: combustion (total radiaoactivity in urine and faeces); one-step digestant-scintillant treatment (blood); enzymatic treatment of urine for metabolite identification (ß-glucuronidase, sulfatase, acid) follwoed by filtering


ANALYSIS
- Method type(s) for identification: GC-MS, HPLC-MS-MS, Liquid scintillation counting, TLC

Results and discussion

Signs and symptoms of toxicity:
not specified
Dermal irritation:
not specified
Absorption in different matrices:
- Non-occlusive cover + enclosure rinse: 11.43%
- Skin wash: 38.95%
- Skin test site: 34.99%
- Urine: 3.32%
- Cage wash + cage wipe:
- Faeces: 0.57%
- Expired air (if applicable): 1.84%
Total recovery:
- Total recovery: 91.97%
- Recovery of applied dose acceptable: yes
- Results adjusted for incomplete recovery of the applied dose: no
Percutaneous absorption
Dose:
1 g/kg bw
Parameter:
percentage
Absorption:
ca. 7 %
Remarks on result:
other: 96 h
Remarks:
absorption rate: 0.57 mg/cm²/h

Any other information on results incl. tables

Table 4. Recovery of radioactivity from a 6-h, 1.0 g/kg dermal application of neat [14C]2-ethylhexanol to
a 2.27 cm2 area on the clipped backs of female Fischer 344 rats.

Collection period (h)

Sample

0-8

8-24

24-48

48-96

Total

Urine

1.41 ±0.47

1.66 ±0.25

019±0.03

0.07±0.02

3.32±072

Faeces

0.03±0.02

0.39±0.066

015±0.06

0.01±0.01

0.57±0.09

Cage wash (water)

0.58±0.13

0.24±0.03

      0.04±0.01

0.03±0.01

0.87±0.

Silica gel breath traps

0.94±0.83

0.40±0.16

      0.04±0.01

0.03±0.01

1.41±0.92

Sodium hydroxide breath traps

0,24±0.04

0.13±0.07

  0.03±0.01

0.03± 0.01

0.43±0.06

Dose recovered from the
exposure site at 6h

34.99±16.61

Washing recovery from the
exposure site at 6h

38.95±9.78

Dose on cell cover at 6h

11.43±5.17 +5.17

Total recovery

3.19

±0.77

 2.81±0.38

     0.44±0.11

0.17±0.03

91.97±5.75

Values are the mean per cent of dose SSD recovered from four animals.

Table 5. Recovery of radioactivity following a 1 mg/kg i.v. (tail vein) dose of [14C]2-ethylhexanol (in
saline) to female Fischer 344 rats.

Collection period (h)

Sample

0-8

8-24

24-48

48-96

Total

Urine

35.79±1.89

14.50+2.99

1.59±0.28

1.40±0.26

53.28±3.70

Faeces

0.19±0.30

2.89±0.95

0.55±0.15

0.22±0.05

3.84±1.19

Cage wash (water)

15.94±3.36

3.66±1.74

0.66+0.28

0.92±0'44

21.17±2'92

Silica gel breath

0.22 ± 0.03

0.15±0.04

0.04 ±0.01

0.03 ± 0.01

0.44± 0.07

traps

Sodium hydroxide

19.12 ± 1.02

2.15±0.18

0.94±0.11

0.77±0.07

22.97±1.23

breath traps

Total recovery

71.24±3.42

23.35+3.01

3.77±0.67

3.33±0.42

101.69±1.11

Values are the mean per cent of dose +/- SD recovered from four animals


Table 6. Quantitation of urinary metabolites of 2-ethylhexanol in female Fischer 344 rats.

Per cent of dose per peak

Single low oral dose

Single high oral dose

Repeated low oral dose

Dermal dose

Peak ID

Free

Glucuronide

Free

Glucuronide

Free

Glucuronide

Free

Glucuronide

5-OH-EHA

1.11±0-64

1.28±1.26

3.06±0.88

1.18±0.77

0.73±0.21

2.93±2.27

<0.01

0.30±0.37

2-Ethyladipate +

5-OH-EHA

5.55±2.27

24.12±6.84

4.13+0.95

8.17+4.09

2.37+1.62

25.30±2.19

<0.01

1.61±0.37

6-OH-EHA

1.56±1.10

6.81+1.97

0.80+0.71

6.26±0.55

1.43±0.87

6.89±1.65

<0.01

0.57±0.32

Lactones of 5-OH-EHA

0.44±0.17

0.19±0.25

0.28±0.05

0.01

0.56±0.41

0.82±1.54

<0.01

0.01

2-Ethyl-5-hexenoic acid

<0.01

0.16±0.11

0.01

0.10±0.13

0.06±0.12

0.20±0.11

<0.01

0.01

EHA

0.54±0.68

6.30±1.21

4.77±3.69

20.14±3.25

1.27±1.08

7.45+2.42

<0.01

0.52±0.23

2-Ethylhexanol

0.03+0.05

1.53±0.51

0.01

0.34±0.31

0.22±0.40

1.19±0.15

<0.01

0.06±0.07

Values represent the mean±SD of four animals over the 0-24-h collection period. Quantitation is based on hplc separation and radiochemical detection of metabolites. The structural assignments are based on hplc and glc-mass selective detection analysis of samples and authentic standards both

before and after enzymic hydrolysis.


  • Dermal absorption was low. This is also reflected by the low AUC (4.6 µg-eqivalent/g x h) compared to the i.v. studies (87.2 µg-eqivalent/g x h) which was conducted at a 1000 -fold lower dose level (1 mg/kg bw9.
  • The metabolic pattern was similar to that seen after oral gavage (cf. attached document in cross-referenced study summary). Occurence of 3% of the dose in faeces was discussed to result from biliary excretion of conjugates.

    1.  Excretion balance studies were conducted with 2-ethylhexanol (2-EH) in femaleFischer 344 rats following single high (500 mg/kg) and low (50 mg/kg) oral doses of [14C]2-El, following repeated oral dosing with unlabelled 2-EH at the low level, following dermalexposure for 6 h with a 1 g/kg applied dose of [14C]2-EH, and following a 1 mg/kgi.v. doseof [14C]2 -EH.

    2.  The high, low and repeated low oral dose studies with 2-EH showed similar excretion balance profiles of [14C], with some evidence of metabolic saturation at the high dose.

    3.  No evidence of metabolic induction was seen following the repeated low oral dosing.

    4.  All of the oral doses were eliminated rapidly, predominantly in the urine during the first 24 h following dosing.

    5.  The dermal dosing resulted in only about 5% absorption of the 1 g/kg dose, with the major portion of the dose recovered unabsorbed from the dermal exposure cell at 6 h.

    6.  Urinary metabolites eliminated following the oral and dermal doses were predominatelyglucuronidesof oxidized metabolites of 2-EH, includingglucuronidesof 2-ethyladipoic acid, 2-ethylhexanoic acid, 5-hydroxy-2-ethylhexanoic acid and 6-hydroxy-2-ethylhexanoic acid.

Applicant's summary and conclusion

Conclusions:
Bioavailability of 2-EH via the dermal route is low. Metabolism and excretion of absorbed material is fast, with no difference to the oral route.
Executive summary:

2-EH was only slowly absorbed following dermal application of 1 g/kg bw. Less than 7% of the dose was absorbed within 6 hours of skin contact. The absorbed dose underwent rapid oxidative metabolism and glucuronidation followed by rapid excretion, predominantly in the urine. The absorption rate was 0.57 mg/cm²/h, which is in the range that was determined for rat skin in vitro (0.22 mg/cm²/h; Barber et al., 1992). The metabolic pattern was similar in all experiments, i.e. there were no differences that could be attributed to the oral or dermal route, the low or high dose level, or to single or repeated treatment. One exception is the marginally delayed excretion at 8 hours after dosing in the group receiving the high oral dose which indicates some saturation of the metabolic capacity (Deisinger, 1994).