The use of animal testing has significant benefits in medical research; however, increased costs, extremely high failure rates, and delays in drug approval have led many to re-evaluate its value in drug development.
The concordance between animal and human trials
A high rate of withdrawal of new drugs during or even after clinical trials is due to lack of efficacy or adverse side-effects, which were not identified during expensive and time-consuming preclinical testing, mainly animal testing.
Animal models are traditionally utilized to find targets for disease; however, there are significant challenges in terms of predictability or reliability on these models and transferability of the results to humans. Animal models are unable to replicate the human pathophysiology entirely and hence cannot predict mechanisms involved in human diseases accurately.
Drugs that survive clinical trials and attain market approval may still be recalled later due to toxicity identified only after months or years of in-human use. As per WITHDRAWN (2016 data), a public resource for withdrawn and discontinued drugs, of the 578 discontinued and withdrawn drugs in Europe and the United States, almost one-half were withdrawn or discontinued in post-approval actions due to toxicity. A study by Van Meer et al. found that of 93 post-marketing serious adverse outcomes, only 19% were identified in preclinical animal studies. The most common toxicity types associated with drug withdrawals in the United States and Europe are hepatic (21%), cardiovascular (16%), hematological (11%), neurological (9%), and carcinogenicity (8%).
When animal tests falsely identify a safe chemical as "toxic”
Probability of false-positive toxicity findings with animal studies is also a matter of concern. When animal tests falsely identify a safe chemical as "toxic," the almost inevitable outcome is the abandonment of further development. Undoubtedly many potentially beneficial drugs have failed animal testing and been lost to patients, even though they would have been both safe and effective. Because a drug that shows toxicity in animal models is unlikely to ever undergo human testing, the proportion of this type of "error" is unknown. Many highly beneficial drugs would have failed animal testing and would have never reached the market, however; they were developed before animal testing was required. A well-known example is penicillin, which is fatal to guinea pigs and paracetamol, which is toxic in dogs and cats.
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