Ethyl acetate

Skin irritation / corrosion

Administrative data

Endpoint:

skin irritation: in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

This experiment was specifically carried out to quantify the irritancy of ethyl acetate to assess its potential in transdermal drug delivery patches. The work is well reported and carried out to a protocol closely matching OECD 404. The ethyl acetate was not in direct contact with the skin of the test animals (separated by a 50um membrane) but in contrast exposure time was significantly longer than usual

Data source

Reference

Reference Type:

publication

Title:

"Cutaneous effects of transdermal levonorgestrel"

Author:

Friend, DR, Phillips, SJ, Hills, JR

Year:

1991

Bibliographic source:

Fd Chem Toxic. Vol 29 (9) 639-46.

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 404 (Acute Dermal Irritation / Corrosion)

Deviations:

yes

Remarks:

test substance not placed in direct contact (50um semi-permeable membrane separated test solvent from skin) but occlusion should not make this a material difference. Exposure time 24 hours.

Principles of method if other than guideline:

Evaluation of cutaneous side effects of transdermal patches delivering the drug levonorgestrel and ethyl acetate as a potential skin penetration enhancer. Test not performed according to OECD protocol but similar methodology used.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Ethyl acetate

EC Number:

205-500-4

EC Name:

Ethyl acetate

Cas Number:

141-78-6

Molecular formula:

C4H8O2

IUPAC Name:

ethyl acetate

Details on test material:

- Test substance: reagent grade obtained from Aldrich Chemical company, USA.
- Ethyl acetate tested as the vehicle for the drug levonorgestrel, which was also present in the test formulations (concentration not specified) The formulation tested was in the form of a gel created by adding 2% wt hydroxypropyl cellulose.

Test animals

Species:

rabbit

Strain:

New Zealand White

Details on test animals or test system and environmental conditions:

Rabbits were individually identified on the right ear using permanent ink marker.

TEST ANIMALS
- Source: Elkhorn Rabbitry (Watsonville, CA, USA).
- Weight at study initiation: 2-3 kg
- Housing: individually
- Diet: Purina rabbit chow ad libitum
- Water: uv purified drinking water ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature: 22±2°C
- Humidity: 40-50%
- Photoperiod: 12 hour light/12hour dark cycle

Test system

Type of coverage:

other: un-occlusive

Preparation of test site:

shaved

Vehicle:

unchanged (no vehicle)

Controls:

not specified

Amount / concentration applied:

0.5ml of a gelled (2% weight of hydroxypropyl cellulose) suspension of the drug Levonorgestrel (1.5%) in ethyl acetate. Effectively therefore 96.5% ethyl acetate test solution.

Duration of treatment / exposure:

3-7 patches were placed on each rabbit on new sites over the course of the experiment. Each patch remained in contact with the rabbits skin for 24 hours.

Observation period:

7 days

Number of animals:

4

Details on study design:

TEST SITE
- Area of exposure: dorsal area
- Type of wrap if used: non-occlusive Keri-towels secured with cloth surgical tape. Test cells were held in place for 24 hours after which another cell was placed in a different place for a further 24 hours. Collars were used on the rabbits.

SCORING SYSTEM: Each test site was subsequently assessed using the Draize scoring method (0 to 4) for erythema and odema at 0, 24, 48 hours and 7 days. The irritation index was calculated (average sum of ethythema and odema across all 4 animals used) Individual scores are not tabulated but results are presented graphically with an indication of variability for ratings or erythema and odema.

OTHER: Microscopic examinations were performed on skin tissues fixed in neutral buffered 10% formalin. Samples were routinely processed, embedded in paraffin, sectioned at 5 um, and stained with haematoxylin and eosin. Microslides were examined by light microscopy and the results tabulated.

Results and discussion

In vivo

Results

Results 1

Irritation parameter:

primary dermal irritation index (PDII)

Basis:

mean

Time point:

other: 24 h

Score:

1.7

Max. score:

8

Reversibility:

not fully reversible within: 7 days

Remarks on result:

other: tested using membrane polymer formulation 1

Results 2

Irritation parameter:

primary dermal irritation index (PDII)

Basis:

mean

Time point:

other: calculated from 24, 48, 72 hour observations

Score:

1.3

Max. score:

8

Reversibility:

fully reversible within: 7 days

Remarks on result:

other: tested using membrane polymer formulation 2

Results 3

Irritation parameter:

erythema score

Basis:

mean

Time point:

other: average of 24, 48, 72 hour readings

Score:

1.33

Max. score:

4

Reversibility:

not fully reversible within: 7 days

Remarks on result:

other: tested using membrane polymer formulation 1

Results 4

Irritation parameter:

erythema score

Basis:

mean

Time point:

other: average of 24, 48, 72 hour readings

Score:

0.4

Max. score:

4

Reversibility:

not fully reversible within: 7 days

Remarks on result:

other: tested using membrane polymer formulation 2

Irritant / corrosive response data:

Ethyl acetate, when used as a penetration enhancing solvent for drug delivery through a permeable membrane, produced mild erythema and no oedema, hence its scores are expressed only as a primary irritation index (membrane formulation 1, ethylene vinyl acetate , 7.5% vinyl acetate/polybutylmethacrylate copolymer. Across the membrane formulation 2 (ethylene vinyl acetate, 9% vinyl acetate copolymer) produced mild erythema and very slight odema but these did not fully resolve within the 7 day observation window.

Any other information on results incl. tables

Two formulations were tested with differing membrane composition but both based on 100% ethyl acetate.

Formulation 1 (membrane 1)

	24 hours	48 hours	72 hours	7 days
Erythema	1.6	1.3	1.1	0.7
Odema	0.7	0.2	0.3	0.2
PII	2.3	1.5	1.4	0.9

Formulation 2 (membrane 2)

	24 hours	48 hours	72 hours	7 days
PII	1.5	1.3	1.0	0

Maximum Primary irritation index (PII) possible is 8.

Note that the control using water only produced slight irritation, indicating some contribution to overall irritancy from the test membranes.

Applicant's summary and conclusion

Interpretation of results:

slightly irritating

Remarks:

Migrated information Criteria used for interpretation of results: other: criteria of author

Conclusions:

There are no known reports of levonorgestrel causing irritancy. Some residual irritancy may have been caused by adhesive remaining on the skin following test cell removal. There was also evidence for some contribution to mild irritancy from the membranes themselves. The results indicated that using pure ethyl acetate in a transdermal delivery device is mildly to moderately irritating to rabbits.

Histological examination showed increased cellularity in the papillary and reticular dermis mile hyperkeratosis and scale crust formation. The histological changes were reversible and consistent with a very mild subacute irritation as suggested by the visual assessment. The conclusion was that use of ethyl acetate in a transdermal delivery device is mildly to moderately irritating to rabbits and would be expected to be non to mildly irritating to humans.

This study is not ideal but is deemed sufficiently reliable to characterise the skin irritancy properties of ethyl acetate.

Executive summary:

A study to examine ethyl acetate as a permeation enhancer solvent for transdermal drug delivery reported mild to moderate irritation to rabbit skin following application of a transdermal drug delivery device containing the drug levonorgestrel and neat ethyl acetate. Control devices containing only water were also found to be mildly irritating. Some residual irritancy may have been caused by adhesive remaining on the skin following test cell removal or the semi-permeable membrane used in the device. Whilst the solvent was not in direct contact with the skin (separated by the 50um membrane), the duration of exposure was significantly longer than required for a guideline study. This study is deemed sufficiently reliable to characterise ethyl acetate as not significantly irritating to the skin.