Scanning individuals' genotypes is the best way to improve drug safety. Prescribing the right drug for the right people is called personalised medicine. It is already practiced for some chemotherapy drugs but could be used far more widely. The cutting edge of science is focused on variation between individuals not between entirely separate species.
Technically humans are animals, so what's the big difference?
Whereas all animal cells have properties in common - a nucleus, mitochondria and so on - we now know that even smaller idiosyncrasies distinguish the way the cells of different species react to food, environment and medicines. Failed animal experimentation has irrevocably proven that tiny differences can prevent disease in one species or enable it in another. The smallest biological differences between humans and animals lead to lethal errors when applying animal data to humans. White blood cell surface receptors, for example, leave humans uniquely vulnerable to AIDS. Even the animal experimenters' bible, The Handbook of Laboratory Animal Science, states:
"It is impossible to give reliable general rules for the validity of extrapolation from one species to another. [This] can often only be verified after the first trials in the target species [humans]. Extrapolation from animal models. . . will always remain a matter of hindsight."