1.5.2.1.
Preparations
Healthy young adult albino guinea-pigs are acclimatised to the laboratory conditions for at least five days prior to the test. Before the test, animals are randomised and assigned to the treatment groups. Removal of hair is by clipping, shaving or possibly by chemical depilation, depending on the test method used. Care should be taken to avoid abrading the skin. The animals are weighed before the test commences and at the end of the test.
1.5.2.2.
Test conditions
1.5.2.2.1. Test animals
Commonly used laboratory strains of albino guinea-pigs are used.
1.5.2.2.2. Number and sex
Male and/or female animals can be used. If females are used, they should be nulliparous and non-pregnant.
A minimum of 20 animals is used in the treatment group and at least 10 animals in the control group.
1.5.2.2.3. Dose levels
The concentration of test substance used for each induction exposure should be the highest possible to produce a mild but not excessive irritation. The concentration used for the challenge exposure should be the highest non-irritating dose. If necessary, the appropriate concentration can be determined from a pilot study using two or three animals.
For water soluble test materials, it is appropriate to use water or a dilute non-irritating solution of surfactant as the vehicle. For other test materials 80 % ethanol/water is preferred for induction and acetone for challenge.
1.5.2.3.
Procedure
1.5.2.3.1. Induction
Day 0-treated group
One flank is cleared of hair (closely-clipped). The test patch system should be fully loaded with test substance in a suitable vehicle (the choice of the vehicle should be justified; liquid test substances can be applied undiluted, if appropriate).
The test patch system is applied to the test area and held in contact with the skin by an occlusive patch or chamber and a suitable dressing for six hours.
The test patch system must be occlusive. A cotton pad is appropriate and can be circular or square, but should approximate 4-6 cm
2
. Restraint using an appropriate restrainer is preferred to assure occlusion. If wrapping is used, additional exposures may be required.
Day 0-control group
One flank is cleared of hair (closely-clipped). The vehicle only is applied in a similar manner to that used for the treated group. The test patch system is held in contact with the skin by an occlusive patch or chamber and a suitable dressing for six hours. If it can be demonstrated that a sham control group is not necessary, a naive control group may be used.
Days 6-8 and 13-15-treated and control group
The same application as on day 0 is carried out on the same test area (cleared of hair if necessary) of the same flank on day 6-8, and again on day 13-15.
1.5.2.3.2. Challenge
Day 27-29-treated and control group
Feedback