ABSTRACT
The viability of new drug development is critically dependent on the success rates that pharmaceutical firms face when they decide to pursue promising investigational drugs. Despite the fact that when a new drug enters the development pipeline the expectations of the drug’s sponsor are that this particular drug will succeed in development and reach the marketplace, an undeniable axiom of drug development is that only a small percentage of such drugs will actually make it to market. Drug developers are well aware of this reality, but they must make decisions to proceed with clinical testing of investigational drugs on the basis of limited information about what their effects, good and bad, will be in humans. Depending on the type of drug and the condition that the drug is intended to treat, animal models can be more or less useful in making predictions about the effects in humans. In all cases, though, the uncertainty is substantial.
