The bulk of this book is devoted to the practical questions of ‘what toxicological studies should we perform?’ and ‘how should we perform them?’ In this first chapter we consider some of the more philosophical questions of toxicology; the ‘whys?’, the ‘whens?’ and the ‘on whats?’

Compounds which undergo toxicity testing may be conveniently categorised as those which are intended for administration to man and those which are not. The former include Pharmaceuticals to be used medicinally or prophylactically and chemicals which are added to our food, drinks or medicines to improve their stability, appearance or palatability. Those compounds which are not intended for human consumption can nevertheless represent a toxic hazard to man if they find their way into the food chain or are consumed accidentally or on purpose. This category includes biocides of various types, environmental contaminants, industrial chemicals, veterinary products, animal feedstuffs, food additives, household chemicals and natural toxins.

Since it is on pharmaceuticals that the most comprehensive toxicological evaluations are generally performed, this book has been directed primarily towards the toxicological evaluation of potential new drugs. The principles and methodology of toxicological evaluation of other types of compounds are essentially similar. We shall not, in this book, consider aquatic and environmental toxicology.

THE PURPOSE OF TOXICOLOGICAL TESTING

It was recognised over 400 years ago, by a remarkable character, Phillipus Theophrastus Bombastus von Hohenheim (1493–1541) who called himself Paracelsus, that all compounds are toxic.