Argument: Medicines tested successfully on animals can prove toxic to humans

Issue Report: Animal testing


Arthur Allen. “Of Mice or MenThe problems with animal testing.” June 1, 2006 – “But just how often do animal tests predict side effects in humans? Surprisingly, although it is central to the legitimacy of animal testing, only a dozen or so scholars over the past 30 years have explored this question. The results, such as they are, have been somewhat discouraging. One of the scientists, Ralph Heywood, stated in 1989 that “there is no reliable way of predicting what type of toxicity will develop in different species to the same compound.” The concordance between man and animal toxicity tests, he said, assessing three decades of studies on the subject, was somewhere below 25 percent. “Toxicology,” concluded Heywood, “is a science without a scientific underpinning.”

In 1999, the Health and Environmental Science Institute, a Washington, D.C.,-based group that brings together business, academic, and government experts to assess risks in public health, began a thorough examination. Working with confidential data provided by 12 pharmaceutical companies on 150 compounds that had produced a variety of toxic effects in people, an institute-hosted workshop found that only 43 percent of the drugs produced similar problems in rodents, and 63 percent did so in nonrodents. These are not reassuring numbers. (Though they would look better if the institute’s review had included the 90 percent of drug candidates that are screened out by animal toxicity, and thus never even tested on humans.)

Industry, academic, and government scientists agree that science is in need of better animal models for testing drug safety. “Put simply, the inability to predict the human toxicity of drugs is what’s breaking the promise of genomics to drug development,” says Paul Watkins, a North Carolina physician who is advising the institute. The high-tech biology era has seen the discovery of thousands of new targets for pharmaceuticals, but the number of drug failures remains as high as ever. It’s painful for the drug industry when $500 million goes toward developing a drug that then must be scrapped because of side effects that only surface in human trials. And it’s bad for the public as well when a product like Rezulin, Warner-Lambert’s diabetes drug, is withdrawn from the market for causing liver disease and deaths after 800,000 patients have taken it.”