[expat]

There are countless examples in the medical journals where drugs and other chemicals react differently in people and animals (7):

* cortisone produces birth defects in mice but not people, whilst thalidomide works the other way around;
* morphine calms people but excites cats, goats and horses;
* penicillin is highly poisonous to guinea pigs and hamsters;
* insulin causes birth defects in animals but not in people;
* the antibiotic chloramphenicol produces the blood disease aplastic anaemia in some human patients but it saves animals;
* in dogs, the muscle-relaxing drug tubocurarine causes a severe fall in blood pressure but is comparatively safe for people (8);
* and doses of aspirin used in human therapeutics are poisonous to cats.


Experiments sometimes claim that species differences are rare. But in fact they occur frequently. Surveys have shown that most of the side-effects occurring in people when they take a drug cannot be correctly predicted by animal experiments (7). Nor can the problem be overcome by using more species of animals.
This is illustrated by the drugs aspirin and fenclozic acid (7). Aspirin causes birth defects in rats, mice, cats, dogs, guinea pigs and monkeys but is considered safe for pregnant women. The arthritis drug, fenclozic acid, causes liver toxicity in people but not in rats, mice, dogs, monkeys, rabbits, guinea pigs, ferrets, cats, pigs and horses.