The Tragedy of Thalidomide and the Failure of Animal Testing

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In the late 1950s and early 1960s, the drug thalidomide caused an estimated 10,000 birth defects and thousands of fetal deaths worldwide. The affected babies typically suffered from phocomelia, a failure of the limbs to develop. These unfortunate children were cruelly referred to as "flipper babies." Thalidomide had been prescribed to pregnant women to help reduce morning sickness, but tragically, it turned out to be toxic to developing fetuses.

Responding to a public outcry regarding drug safety, the U.S. Congress passed the previously unpopular Kefauver-Harris Act in October of 1962, which, among other things, mandated that all drugs undergo preclinical testing to demonstrate their safety and effectiveness. The FDA has interpreted these preclinical standards as a call for mandatory animal testing. This interpretation expressed the will of the bill's sponsor, Senator Estes Kefauver, but was based on a misunderstanding of the science behind drug testing. The politician mistakenly argued that thalidomide had never been tested on animals and that it was this lack of animal testing that had led to its disastrous clinical use.

In fact, extensive animal testing had failed to predict any hazards from thalidomide, and the drug was made available to doctors largely because of the existing animal data. According to James L. Schardein, an expert in teratogens (birth defect-causing substances), "In approximately 10 strains of rats, 15 strains of mice, 11 breeds of rabbits, 2 breeds of dogs, 3 strains of hamsters, 8 species of primates and in other such varied species as cats, armadillos, guinea pigs, swine and ferrets in which thalidomide has been tested, teratogenic effects have been induced only occasionally." Moreover, the few animals who did experience birth defects did so only with exposure to huge concentrations of thalidomide. For example, causing deformities in New Zealand white rabbits required drug concentrations between 75 and 300 times the level of human exposure. It is unquestionable that thalidomide is not a teratogen in the vast majority of species and that animal data did not predict the human response. Thus the FDA's animal-testing policy stems largely from a misunderstanding of the facts surrounding the thalidomide case.

Sadly, the 1962 Drug Amendments are still interpreted as mandating animal testing, despite advances in other toxicology technologies that render animal tests increasingly obsolete. It has been shown conclusively that testing on human tissue in vitro could have predicted the danger that thalidomide posed. In vitro testing, computer modeling, and other technologies are increasingly surpassing animal models in both accuracy and efficiency, but the U.S. has yet to adapt its regulatory process to acknowledge these changes. Instead, the continuing mandate on animal testing serves to entrench ineffective and anachronistic testing methods and to stifle the development of new testing methods. As a result, the animal research industry has grown, health-care costs have risen, and medical progress has slowed. And despite the vast expenditure on animal toxicity testing, drugs remain unsafe, and tragedies continue to occur.

On September 30, 2004, the drug company Merck recalled its popular pain reliever Vioxx from the market because it was found to increase the risk of blood clots in patients. Evidence suggests that human observational data predicted these effects as early as 1996, and human clinical data confirmed the danger in 2001. However, animal tests supported the release and continued use of the dangerous drug, so Merck chose not to conduct human trials on Vioxx's relationship to blood clotting. Because Vioxx remained on the market, the FDA has estimated that as many as 27,000 patients may have died. Alise Reicin, vice president of clinical research at Merck Research Laboratories, has defended Merck's conduct by stating that animal studies suggested that Vioxx might actually reduce the risk of heart disease and stroke. The Vioxx debacle is not an isolated incident or the result of a failure of individuals. The American public was failed by the FDA's drug approval procedures.

Like the thalidomide disaster, the Vioxx fiasco can be attributed not to a lack of animal tests, but to inadequate human in vitro and clinical testing. More than 106,000 people die every year from adverse reactions to animal-tested drugs, and another 2.2 million are seriously injured. Such reactions make animal-tested drugs the fourth leading cause of death and cost the U.S. more than 136 billion in health-care dollars. These numbers suggest that the FDA and the medical profession do not adequately understand the way drugs will affect individuals, groups, or the population in general. The role of animal tests in this ignorance is highlighted by the fact that 92 percent of animal-tested drugs are rejected in clinical trials, and more than 50 percent of those few drugs that do reach the market are removed or relabeled because of unforeseen harm to patients. Thus animal testing fails to catch more than 96 percent of the problems with drugs, and clinical trials remain too brief and narrow to fully compensate for the failures of animal experimentation. Moreover, it is reasonable to assume that animal testing fails to uncover an equally large percentage of the actual benefits to humans that drugs offer. Therefore, the American public is losing out on both ends, and we are paying for these losses with our health problems, rising health-care costs, and high taxes.

Despite the wealth of evidence against animal experimentation, a fearful public demands a tangible response to episodes like the thalidomide disaster. Unfortunately, many members of Congress, researchers, and drug companies find blanket animal testing to be a simple, if crude, way to reassure the public that American medicine is completely safe. Animal testing also provides liability coverage for drug companies and abundant grants for the research community. Clearly, many interest groups benefit from the continued use of animals in medical research. However, animal testing does little to protect public health or to advance the cause of medicine.

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