Toxicological Evaluation of Product Safety ROBERT P. GIOVACCHINI, Ph.D. *
Toxicology was once considered to cover only the study of poisons. Today it has expanded to include the evaluation of all aspects of hazards to man from substances with which he may come in contact.
DEFINITIONS Virtually all such substances can present a hazard under appropriate conditions and concentrations. Thus the definitions of such terms as "poison," "toxicity," and "hazard" are of fundamental importance in establishing criteria for evaluating product safety. There are basically two types of definitions, which mayor may not coincide at any time. The first is the definition established through accepted scientific usage. The second is the definition adopted for regulatory purposes by governmental laws and regulations. The term "poison" has been used generally by the scientific community to mean a substance that, when used in small amounts, is injurious to health or dangerous to life. The term "toxicity" has been used to describe the degree of poisonous hazard presented by a given substance. Although toxic foods and drugs have been subjected to federal regulations since 1906, the first federal legislation designed speCifically to control poisons was the Caustic Poison Act of 1927. In that statute, Congress avoided defining such terms as "poisons" or "hazard" by simply listing all the chemicals that were considered sufficiently dangerous to regulate. The Federal Hazardous Substances Act of 1960 (FHSA), as amended in 1966 and 1969, has now displaced the earlier legislation, except for foods, drugs, and cosmetics. Under the FHSA, traditional toxicological terms have been given very definite content. A substance is considered "highly toxic" if it produces death in half or more than half of a statis':'Vice President, Medical Evaluations, The Gillette Company Research Institute, Rockville, Maryland
Pediatric Clinics of North America- Vol. 17, No.3, August, 1970
tic ally significant number of animals after either oral feeding, inhalation, or topical application at a dose level of 50 mg. per kg. or less (oral), 200 parts per million (2 mg. per liter) or less (inhalation), or 200 mg. per kg. or less (topical), or is determined by the Commissioner of Food and Drug to be "highly toxic" on the basis of human experience. A substance is considered "toxic" if oral doses from 50 mg. per kg. to 5 gm. per kg. (and corresponding dose levels in inhalation or topical application) produce death in half or more than half of a statistically significant number of animals or if the Commissioner of Food and Drug determines it on the basis of human experience. A "primary irritant" means a substance that is not corrosive, but is a primary irritant according to available data of human experience or which, when tested by an animal test described in the regulations, gives a prescribed dermal irritancy score. A substance is considered an "ophthalmic irritant" if the available data on human experience indicate that it is an irritant for the eye mucosa, or when tested by the prescribed rabbit eye test, the animal's eyes show, at 24, 48, and 72 hours, discernible opacity or ulceration of the cornea or inflammation of the iris, or a diffuse deep-crimson red of the conjunctivae with individual vessels not easily discernible, or an obvious swelling with partial eversion of the lids. A "corrosive substance" is one that causes visible destruction or irreversible alterations in the tissues at the site of contact. The test for a corrosive substance is whether, by human experience or appropriate animal tests, such tissue destruction occurs at the site of application. A "strong allergic sensitizer" is defined as a substance that produces, by means of an "antibody mechanism," an allergic reaction in a substantial number of persons who come in contact with it. A "photodynamic sensitizer" is a substance that causes an alteration in the skin or mucous membrane so that when these areas are subsequently exposed to ordinary sunlight or equivalent radiant energy an inflammatory reaction will develop. The FHSA definitions and animal screening tests provide a useful outline for undertaking a thorough safety evaluation of a consumer product. But no set of artificial or rigid rules, regulations, and definitions can control the toxicologists' responsibility for determining from animal tests that a proposed new product or ingredient is safe for human use under conditions of recommended use and potential misuse. As the FHSA itself recognizes, evidence of safety or hazard in humans ultimately must prevail over contrary evidence obtained from animal screening tests. The data obtained from poison control centers and physicians are very useful in indicating where product hazards may and may not exist. Accidental ingestion or misuse provides an opportunity for direct human evaluation of a type that would, of course, be wholly improper on an experimental basis. Physicians and hospitals should be urged to report all such results to product manufacturers and to poison control centers, whether or not it involves any hazard to health, in order to develop a better understanding of the correlation between animal screening tests and human experience.
TOXICOLOGICAL EVALUATION OF PRODUCT SAFETY
GENERAL PRINCIPLES All substances are potential toxicological hazards. Balancing a compound's or product's utility against its toxicological hazards is often difficult, particularly because the worst conditions of abuse or misuse cannot always be foreseen. Nor has there been devised any set of animal toxicological, pharmacological, biochemical, or physiological tests which can demonstrate all the possible effects of a new substance or product in the human. In evaluating the toxicological potential of a material or product, the toxicologist must concern himself with not only gastrointestinal absorption but also dermal, ophthalmic and pulmonary absorption and irritation. There is a tendency, due probably to the limited availability of toxicological information and knowledge, to assume that substances which are closely related chemically have similar toxicological properties. While this is often true, it is not universally true. Toxicological evaluation by analogy therefore can be misleading. Dependent upon minor differences of the original chemical structure, intermediate compounds formed as a result of the detoxification process after absorption by the body can produce different and in some cases more toxic intermediates and end products. In order to make the determination that a new product is safe for its intended use, one must first review (1) the known toxicological information on each ingredient, (2) its volume and level of concentration, (3) its potential physiological effects, (4) the combination of intermediates that may form, (5) the method of dispensing, and (6) the extent of proposed human exposure. The above is also true when only one ingredient is involved. The medical, chemical, and pharmacological literature must be critically reviewed for background information. When little or no information on a new ingredient is available from the literature, sufficient toxicological testing must be done to ascertain where the new ingredient fits on the toxicological ladder. After the literature review, a preliminary toxicologic~l judgment can usually be made. Any ingredient with a known problem history should be removed from the formulation and replaced with adequate and less toxic ingredients. If this is not possible, then thought should be given to reducing the potential consumer hazard through adequate labeling and proper containers. The possible effects of removing the ingredients from or detoxifying them in the gastrointestinal tract, if the mixture is accidentally ingested, must also be considered. If it appears that the ingredient will react differently in a mixture, animal testing should be designed to evaluate that ingredient in the specific mixture. In all instances, the final product must be tested using the ingredients that will be used if the product is manufactured for public distribution. Adequate specifications must be set for the ingredients and the product to reduce the problem of batch to batch toxicological variation and nonreproducible biological results. In addition, stability data must be obtained to insure that the product is stable under conditions of heat and cold, and that it has the ability to withstand pathogenic bacteriological contamination.
STAGES IN TESTING Over the past 100 years academic, government, and industry pharmacologists and toxicologists have developed an armamentarium of animal screening tests which can determine the quantity of test material required per gram of experimental animal body weight to produce untoward or fatal effects. The terms minimum lethal dose (the smallest quantity known to have produced death), median lethal dose (that which is fatal to a given percentage of a species of animals-usually 50 per cent-abbreviated as LD 50 ), and toxic dose (the dose capable of producing functional derangement in the animal or human) have become part of the toxicologist's vocabulary. Once any substance is inhaled, ingested, or topically absorbed, it will become involved with the intricate chemistry of the body. Some substances will have essentially no effect while others may produce functional (dizziness, nausea), biochemical (detected by clinical chemistry studies), or structural (noted on microscopic organ examination) changes. In attempting to recognize the possible toxicological properties of the product and assess risk, three stages of testing are usually involved. They are (1) animal acute screening studies, (2) animal subacute and chronic studies, and (3) human prophetic patch and use tests. The specific product, its proposed use and proposed exposure will dictate the order and type of tests that should be utilized.
ACUTE TOXICITY Five types of animal screening studies are generally used. They are (1) acute oral toxicity, (2) ophthalmic irritancy, (3) percutaneous toxicity,
(4) dermal irritancy, and (5) sensitization tests. If these studies elicit unexpected or unexplained reactions, additional tests to evaluate the specific problem must be instituted. The most frequently used test is the acute oral toxicity test. Here several doses, spaced according to some geometric or logarithmic progression, are given to a species of animals. At least three dose levels are used. The animals are observed and the number of deaths are recorded daily for a period of 14 days following intubation. Gross and microscopic examinations of various organs are performed in many cases. Too little attention has been paid to subjective observations and possibly too much to objective measures. The physician dealing with acute human oral ingestion is dealing with subjective observation and usually does not have the opportunity for confirmatory laboratory tests. Thus, the subjective observations noted on animal studies can provide valuable information. The animals most used in oral toxicity tests are rats and mice. Voluminous toxicological data have been compiled with these animals, but it cannot be assumed that the results obtained in these species are predictive of human responses. For example, the rat and mouse are resistant to certain chemical agents (aromatic amines, phenols) and
TOXICOLOGICAL EVALUATION OF PRODUCT SAFETY
respond, in many cases, differently than other species. Morphine is a stimulant to the mouse and cat and a depressant to the rat, dog, and man. Not only may animal species react differently to the same material or compound, but sex, age, breed, and weight can create differing toxicological responses and LD50'S in the same species. Thus when working with a new substance, more than one species, sex, age, and weight of animal are used. Other types of hazard testing also do not necessarily predict human responses. For example, materials that are minimal dermal irritants in humans, when applied to shaved rabbits' backs, may show either a severe or minimal response. When severe reactions are produced in the rabbit eye by a test material it does not necessarily follow that the same reaction will occur in the human eye. On the other hand, it is generally believed that when a new substance causes no ophthalmic reactions in rabbits it is highly unlikely to cause ophthalmic reactions in humans. Thus, when concern over rabbit ophthalmic results occurs, dog and monkey ophthalmic studies are instituted in order to obtain data more predictive of human reactions. In many situations these species will demonstrate only minimal transient conjunctival irritation rather than the severe and prolonged corneal, irital, or other ophthalmic damage seen in the rabbit eye. Because the test methods now available are far from perfect, close attention and scrutiny must be paid to all effects noted. Generally, when several dissimilar species demonstrate the same effect to a given substance or product, it is very likely that the human will respond similarly. It is important therefore to review the overall results of preliminary animal screening tests and then evaluate the speCific results on which different data were obtained with a multispecies comprehensive battery of tests which can more specifically isolate the toxicological activity. At all times one must attempt to elucidate the substance's mechanism of action. One must determine the nature and manifestations of the damage (organ, cellular).
SUBACUTE AND CHRONIC TOXICITY Subacute and chronic poisoning, in many cases, offers serious diagnostic problems to the physician. Animal studies which help elucidate these toxicological hazards are subacute and chronic ingestion studies, dermal absorption studies, inhalation studies, and in certain cases teratogenic studies. Subacute and chronic toxicity tests are designed to determine the primary toxic effect of the product when it is used at a low dose level a few times or on a daily basis. It is most important in these to consider carefully not only the product's chemical and physiological properties, but also its intended use. Every class of product and every product within each class presents specific problems. While standard chronic test designs are available and acceptable, one should use or design a type of test protocol that will give the most fruitful information on the particular
product or ingredient, rather than using an all-purpose test which can lead to broad results that do not afford specific conclusions. Other considerations that must be resolved prior to testing are (1) animal species to be used, (2) diet, (3) route and frequency of administration, (4) dosage, (5) number of dose levels, (6) number of treated control and untreated control groups, (7) age, sex, and number of experimental animals, (8) duration of the study, and (9) parameters to be examined (symptomatology, hematology, clinical chemistry and organ function, gross and histopathologic examination). Irrespective of the test design finally employed, it should include one dose level of animals at which signs of toxicity are produced. Since the number of animals exposed to the product can never equal the number of humans who will eventually use it, one cannot expect to detect with any reliability toxic manifestations that may occur in a small minority of human users. Studying large numbers of animals (50 or more per dose level) causes cursory attention to be given to any one. It is far better to study in detail a smaller group (10 to 25) with adequate controls. These controls extend to not only the use of treated control and untreated control animals but also the use of both males and females from a single source and adequate staff to care for the animals and maintain a normal environment for them.
HUMAN PROPHETIC PATCH TESTING Human dermal patch testing aids in eliciting the product or ingredient's potential hazards with respect to (1) primary skin irritancy, (2) contact sensitization, and (3) contact photo-allergic or phototoxic reactions. The particular type of primary skin irritancy test that is run will depend on the intended use of the product and the background information on the propensity of the product or ingredients to be irritants. One can use (1) overnight, semi-occlusive patching, (2) daily patching for 5 or 8 hours for 1 week occlusively, (3) daily occlusive patch testing for 2 weeks, Monday through Friday, and (4) patch testing daily occlusively for 2 weeks, Monday through Friday, a 1 week rest, followed by 4 weeks of product use under label directions, then challenge patches. The latter is a combination irritancy-contact sensitization test. Primary irritancy patch tests should never be run without adequate controls which should include a product that has had extensive safe commercial use. Further, the test design should be such that minimal erythema is produced in some of the test subjects with the control product. Tests such as those described by Brunner, Kligman, and Rostenberg are useful in evaluating potential contact sensitization. The specific test used should be dependent upon the propensity of the product to produce sensitization and its potential use. Curwen and Jillson have described a diagnostic test which, with the following modification, is used to elicit photosensitization potential. The
TOXICOLOGICAL EVALUATION OF PRODUCT SAFETY
test subjects' backs are exposed daily to the proposed new ingredient or product for a minimum of 14 days. During this period the test sites are also exposed to a source of ultraviolet light (11J2 minutes) at least five times (day 1,4,7,10, and 14). Following a short rest period of 4 or 5 days, the diagnostic photo-patch test is conducted.
ANTIDOTAL EVALUATION After a review of the toxicological data the product should be given a relative toxicological rating based on the possible amount that could be ingested, inhaled, or absorbed based on the body weight or surface area-dosage relationship. If antidotal procedures are required they should be developed and tested in appropriate animal species for their efficacy. Generally this involves deciding (1) should the substance or product be removed from the gastrointestinal tract, (2) what antidote, chemical or physiological, should be given, (3) what supportive therapy should also be instituted, and (4) which should be done first. Some thought should also be given to repeating acute oral toxicity studies in young animals. The proposed antidotal procedure as evaluated in animals should be made available, either in writing or by telephone, to qualified individuals and organizations on request. This information should be available for the products that are considered practically nontoxic as well as those that are considered to have some hazard. To the physician both types of information are valuable and may, in many cases, prevent the rigors of antidotal procedures when they are not required.
CONCLUSIONS Toxicological studies are involved biological research programs. It is impossible to set out a specific set of tests and rules that one should follow. Each evaluation must be designed with the background literature, the ingredients, the length of exposure, and the type of use in mind. This is especially true with respect to potential misuse. Thus, throughout its life, the product must always be under scrutiny. New products and new ingredients can produce different toxicological effects and different pharmacological modes of action, based on different chemical structures not only of the ingredients but also of the products of their interactions. Toxicological testing can aid in the replacing of more toxic ingredients with less toxic ones. We can never achieve the use solely of nontoxic ingredients, because under appropriate conditions any substance can produce toxicological effects. Toxicological testing can warn the manufacturer and the physician of the possible side effects which could occur under certain conditions of use and misuse. This, in association with proper labeling, packaging, and education of the consumer, can contribute to safer consumer use of products.
REFERENCES Brunner, M. J., and Smiljanic, A.: Procedure for evaluating skin sensitizing power of new materials. Arch. Dermatol., 66:703, 1952. Code of Federal Regulations. Part 191, Chapter 1, Title 21, revised as of January 1, 1969. Washington, U.S. Government Printing Office, 1969. Curwen, W. L., and Jillson, O. F.: Light hypersensitivity. J. Invest. Dermatol., 34:207, 1960. Kligman, A. M.: The identification of contact allergens by human assay. J. Invest. Dermatol., 47:369, 1966. Lichtfield, J. T., Jr., and Wilcoxon, F.: A simplified method of evaluating dose-effect experi· ments. J.Pharmacol. Exper. Therap., 96:99-113, 1949. Rostenberg, A.: Predictive procedures for eczematous hypersensitivity. A.M.A. Arch. Ind. Health, 20:9, 1959. Wei!, C. S.: Tables for convenient calculation of median-effective dose (LD,. or ED,.) and instructions in their use. Biometrics, 8:249-263, 1952. 1413 Research Boulevard Rockville, Maryland 20850