1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt

Endpoint summary

Description of key information

In accordance with an OECD TG 406 study conducted under GLP conditions in guinea pigs ZMB2 is considered sensitising (Safepharm, 2002).

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Reference 1

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

October - November 2002.

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Conducted according to GLP.

Qualifier:

according to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of study:

guinea pig maximisation test

Justification for non-LLNA method:

A non-LLNA method was used as this study was performed prior to the publication and implementation of the OECD LLNA Test Guideline.

Species:

guinea pig

Strain:

Dunkin-Hartley

Sex:

male

Details on test animals and environmental conditions:

Twenty male albino Dunkin Hartley guinea pigs were supplied. After an acclimation period of at least five days, each animal was selected at random and given a number unique within the study which was written on a small area of clipped rump using a black inedible marker pen. At the start of the main study the animals were in the weight range of 300 to 450g, and were eight to twelve weeks old.
The animals were housed singly or in pairs in solid-floor polypropylene cages furnished with wood flakes. Free access to mains tap water and food was allowed throughout the study.
The temperature and relative humidity were set to achieve limits of 17 to 23 deg C and 30 to 70% respectively. The rate of air exchange was at least fifteen changes per hour and the lighting was controlled by a time switch to give twelve hours continuous light and twelve hours darkness.

Route:

intradermal

Vehicle:

arachis oil

Concentration / amount:

5% w/w formulation of the test material

Route:

epicutaneous, occlusive

Vehicle:

arachis oil

Concentration / amount:

5% w/w formulation of the test material

No. of animals per dose:

Ten test, five control.

Details on study design:

RANGE FINDING TESTS:
The concentrations of test material to be used at each stage of the main study were determined by 'sighting tests' in which groups of guinea pigs were treated with various concentrations of test material. The procedures were as follows:
- Selection of concentration for Intradermal Induction:
Intradermal injections (0.1 ml/injection site) were made on the clipped shoulder of one guinea pig, at a concentration of 5% w/w w in arachis oil BP. The degree of erythema at the injection sites was assessed approximately 24, 48, 72 hours and 7 days after injection. The degree of oedema was not evaluated. Any evidence of systemic toxicity was also recorded. The concentration caused only mild to moderate skin irritation, was well tolerated systemically, and was selected for the intradermal induction stage of the main study.
- Selection of concentration for Topical Induction
Two guinea pigs (intradermally injected with Freud's Complete Adjuvant sixteen days earlier) were treated with four preparations of the test material (50%, 25%, 10% and 5% w/w in arachis oil BP). Applications were made to the clipped flanks under occlusive dressings for an exposure period of 48 hours. The degree of erythema and oedema was evaluated approximately 1, 24 and 48 hours after dressing removal. The highest concentration producing only mild to moderate dermal irritation was selected for the topical induction stage of the main study.
- Selection of concentration for Topical Challenge
Four preparations of the test material (50%, 25%, 10% and 5% w/w in arachis oil BP) were applied to the clipped flanks of two guinea pigs under occlusive dressings for an exposure period of 24 hours. These guinea pigs did not form part of the main study but had been treated identically to the control animals of the main study up to Day 14. The degree of erythema and oedema was evaluated approximately 1, 24 and 48 hours after dressing removal. The highest non-irritant concentration of the test material and one lower concentration was selected for the topical challenge stage of the main study.

MAIN STUDY
A. INDUCTION EXPOSURE
Shortly before treatment on Day 0 the hair was removed from an area approximately 40mm x 60mm on the shoulder region of each animal with veterinary clippers. A row of three injections (0.1 ml each) was made on each side of the mid-line into a 20mm x 40mm area. The injections were:
a) Freund's Complete Adjuvant plus distilled water in the ration 1:1
b) a 5% w/w formulation of the test material in arachis oil BP
c) a 5% w/w formulation of the test material in a 1:1 preparation of Freund's Complete Adjuvant distilled water
Approximately 24 and 48 hours after intradermal injection the degree of erythema at the test material injection sites (i.e. injection site b) was evaluated.
On Day 7 the same area on the shoulder region used previously for intradermal injections was clipped again and treated with a topical application of the test material formulation. A filter paper patch loaded with the test material formulation (50% w/w in arachis oil BP) was applied to the prepared skin and held in place with a strip of surgical adhesive tape covered with an overlapping length of aluminium foil. The patch and foil were further secured with a strip of elastic adhesive bandage wound in a double layer around the torso of each animal. This occlusive dressing was kept in place for 48 hours.
The degree of erythema and oedema was quantified one and twenty four hours following removal of the patches.

- Control animals
The intradermal induction was performed using an identical procedure to that used for the test animals except that the test material was omitted from the intradermal injections. Injection b) was therefore the vehicle alone, injection c) was a 50% formulation of the vehicle in a 1:1 preparation of Freund's Complete Adjuvant plus distilled water. Similarly, the topical induction procedure was idential to that used for the test animals except that the test material was omitted.

B. CHALLENGE EXPOSURE
Shortly before treatment on Day 21, an area of approximately 50mm x 70mm on both flanks of each animal, was clipped free of hair with veterinary clippers.
A square filter paper patch loaded with the test material formulation at the maximum non-irritant concentration (25% w/w in arachis oil BP) was applied to the shorn right flank of each animal and was held in place with a strip of surgical tape. To ensure that the maximum non-irritant concentration was used at challenge, the test material at a concentration of 10% w/w in arachis oil BP was similarly applied to a skin site on the left shorn flank. The patches were occluded with an overlapping length of aluminium foil and secured with a strip of elastic adhesive bandage would in a double layer around the torso of each animal.
After 24 hours, the dressing was carefully removed and discarded. The challenge sites were swabbed with cotton wool soaked in diethyl ether to remove residual material. The position of the treatment sites was identified by using a black inedible marker pen.
Prior to the 24 hour observation the flanks were clipped using veterinary clippers to remove regrown hair.
Approximately 24 and 48 hours after challenge dressing removal, the degree of erythema and oedema was quantified.

Positive control substance(s):

no

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

25%

No. with + reactions:

5

Total no. in group:

10

Clinical observations:

very slight Erythema observations

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: test group. Dose level: 25%. No with. + reactions: 5.0. Total no. in groups: 10.0. Clinical observations: very slight Erythema observations.

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

25%

No. with + reactions:

0

Total no. in group:

10

Clinical observations:

no Oedema observations

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: test group. Dose level: 25%. No with. + reactions: 0.0. Total no. in groups: 10.0. Clinical observations: no Oedema observations.

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

10%

No. with + reactions:

4

Total no. in group:

10

Clinical observations:

very slight Erythema observations

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: test group. Dose level: 10%. No with. + reactions: 4.0. Total no. in groups: 10.0. Clinical observations: very slight Erythema observations.

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

10%

No. with + reactions:

0

Total no. in group:

10

Clinical observations:

no Oedema observations

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: test group. Dose level: 10%. No with. + reactions: 0.0. Total no. in groups: 10.0. Clinical observations: no Oedema observations.

Interpretation of results:

sensitising

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

ZMB2 produced a 50% (5/10) sensitisation rate and is considered a sensitiser to guinea pig skin under the conditions of the test.

Reference 2

Endpoint:

skin sensitisation: in vitro

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

an in vitro skin sensitisation study does not need to be conducted because adequate data from an in vivo skin sensitisation study are available

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
An in vitro or in chemico skin sensitisation study does not need to be conducted because adequate data from an in vivo skin sensitisation study are available (carried out before 11 October 2016).

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

In vivo

In accordance with an OECD TG 406 study conducted under GLP conditions in guinea pigs, a positive result (50% sensitisation) was observed, therefore, ZMB2 is considered sensitizing to the skin (Safepharm, 2002).

Justification for selection of skin sensitisation endpoint:
Key study, conducted to GLP and appropriate OECD Guideline.

In vitro

An in vitro study was not required, given the availability of adequate in vivo skin sensitisation data.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Skin sensitisation:

A positive result of 50% sensitisation was observed in an OECD TG 406 study with ZMB2 (Safepharm, 2002).

Therefore, in accordance with Regulation No. 1272/2008 (amended in Regulation No. 286/2011) Table 3.4.2, ZMB2 is classified as skin sensitiser Category 1B.