388 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the liver and kidneys. Acute effects follow a single application, chronic effects during repeated application over a prolonged period. An indication of the risk is obtained from a pharmacological and toxi- cological study of the drug given orally or parenterally in the normal type of toxicity test. This will allow a comparison between the amount of drug likely to be applied locally, and the dose likely to produce systemic effects. If no systemic effect could reasonably be expected, even if absorption was complete, further study of systemic absorption would not appear to be necessary. If the drug is toxic then the risk of systemic effects may be determined from a measure of the amount of percutaneous absorption from the prepara- tion applied. This may be assessed by established methods in which the amount absorbed is measured in the blood, urine, faeces or some particular organ (2). Radioactive tracer studies increase the sensitivity of such methods. When the compound has a characteristic pharmacological action this may be used for determining the amount of absorption. Thus, in the cat, the uptake of atropine from a suppository can be assessed by measuring the pupil dilatation. Oestrogens can be detected by their effect on the vaginal epithelium or the nipple, in the guineapig. An alternative approach is to measure the amount of the compound which disappears from the site of the application. To actually determine systemic toxicity following dermal application, the compound is applied to the skin and the animal observed for untoward effects. In general, the methods used resemble those utilized in the normal type of toxicity test by the oral and parenteral routes. It is the mode of administration which creates difficulties, making control of dosage and avoidance of oral contamination, a problem. For determination of acute effects, the substance is held in contact with the skin for periods up to 24 hours by means of a rubber sleeve. The pro- cedure and the dimensions of sleeves for different species of animals have been described by Draize (1). The doses applied are calculated on a body- weight basis, and they are introduced under the sleeve which covers approxi- mately 10 per cent of the body surface. By using groups of animals at ascending dose levels it is possible, with toxic substances, to determine the lethal dose (LD5o). Surviving animals are observed for ill effects over a subsequent period of at least two weeks, and this includes observations of their general health, growth and food consumption. The blood and urine are examined for abnormalities and animals showing ill effects are killed for pathological study. Tests for chronic effects are made by applying the substance daily to the same area of skin over a prolonged period of time. Observations are made

TESTING DRUGS FOR DERMAL TOXICITY 389 of the general health of the animal, and the blood and urine are tested from time to time. At the end of the experiment the animals are killed and the main organs and tissues examined histopathologically. Finally, whenever a substance is applied to the skin for a prolonged period of time a danger of carcinogenicity must be considered. An indication of this may be obtained in the chronic toxicity studies, but it is better to set up specific tests. Since most strains of animals have a natural incidence of turnours, it is essential to include an adequate number of controls. Treated and control groups should be of equal size, and should include an equal number of males and females. •ice and rabbits are most frequently used, rats being unsuitable. The test and control groups should contain at least 50 mice and 10 rabbits. The compound, or formulated preparation, should be applied to the same area of skin twice weekly for one year, after which they are observed for a second year. In mice the dorsal skin is used, and in rabbits the dorsal skin or ears. The animals are observed weekly, and the incidence and time of appearance of turnours is recorded in the test and control groups. A full histopathological examination is made of any animals affected during the test, and of all the animals at the end of the experiment. (Received: 8th October 1965.) REFERENCES (1) J. H. Draize Appraisal of the Safety of Chemicals in Foods, Drugs and Cosmetics 46 (1959) (Association of Food and Drug Officials of the U.S.A.). (2) J. W. Hadgraft and G. F. Somers J. Pharm. and Pharmacol. 8 625 (1956). Introduction by the lecturer My paper briefly reviews the main types of tests to which a substance should be subjected for the detection of toxic effects when applied to the skin. It rightly points out that these tests cannot give complete assurance that the substance may be entirely safe. A very real problem, which we have, is our inability to detect sensitizing substances in animal studies. We are concerned with a number of testing procedures firstly local toxicity, that is the local effects when the substance is applied to the skin acute effects refer to single applications, chronic effects to repeated applications. The animal which is used is usually the rabbit and it is interesting to observe that Dr. Levenstein* and I are in a measure of agreement with regard to the use of the pig which has, we recognize, a suitable skin but an unsuitable size. It is my intention, in this brief survey, to bring to your notice various problems which occur in testing for local irritant properties in the rabbit. Certain factors have to be considered firstly we have the prepara- tion of the skin--should it just be clipped, or should we use a chemical * I. Levenstein J. soc. Cosmetic Chemists 15 011 (1964)