It’s common knowledge that many of our medicines are tested in rats. It’s also common knowledge that a rat is not a human, so it should come as no surprise that animal studies can only predict a medicine’s effects in humans with an accuracy of 50% at best — no better than the toss of a coin, argue scientists in a recent letter.

Scientists have written an open letter, published in The Lancet, to UK Prime Minister David Cameron and Health Secretary Andrew Lansley to express concerns about drug failures and adverse drug reactions. The root of the problem? Our reliance on animal tests.

“Our reliance on animals to establish safety results in the exposure of clinical volunteers and patients to many treatments that are at best ineffective and at worst dangerous,” say the authors of the letter. “The stark differences, not only in the diseases of different animal species, but also the ways that they respond to drugs, are now well known.”

Citing figures from the European Commission, the authors claim that adverse drug reactions are responsible for the deaths of approximately 197000 people in the EU, with an estimated total cost of €79 billion. Additionally, the authors blame the rising cost of drugs, and the subsequent burdens on national health services, on drug failures during clinical trials.

“The major reason for the rising cost of new drugs is the fact that more than 90% of them fail in clinical trials. Companies need to recoup the cost of development not only for the drug that succeeds, but for the nine others that fall by the wayside,” explain the authors.

Speaking to Sky News, Tony Dexter, who runs a research lab in Cheshire (UK) and is one of the signatories of the letter, said: “A fundamental problem is that a rat is not a human.”

I’m sure that many of us, although uncomfortable with the subject, will tentatively agree that animal tests are a necessary evil given that such tests are mandated by medicine regulators. Indeed, many important medical advances have been made thanks to our furry friends.

However, I’ve read many health-related research stories about tests in rats and wondered how on earth the results can translate to humans. Here are a couple of news stories I’ve just dug up — all of which are based on rat studies:

Binge-Drinking Teens May Be Risking Future Depression

Maternal Fructose Intake Impacts Female and Male Fetuses Differently

Too Many Sisters Affect Male Sexuality

I’m sure that these studies may potentially translate to human findings, but I can’t really get over my ‘but rats are different to humans!’ mindset. There are a number of similarities between rat genes and human genes, which is why they are frequently used in tests, but does a binge-drinking rat behave the same way as a binge-drinking human?

I also believe that researchers can sometimes get too carried away with the results of animal studies. How many times have we read about an amazing new cancer cure that works in mice? Yes, it’s a fantastic development, but it also raises the hopes of cancer sufferers, even though the research may never translate to humans. In 2007, for instance, there was a really interesting news piece about mice that had been bred to be resistant to cancer.

It’s not just rats and mice where results can fail to translate, there have also been issues in humans following tests in monkeys.

“Take for example the notorious Northwick Park clinical trial drug, TGN1412, that left six young men in intensive care in 2006,” say the authors of the Lancet letter. The drug was demonstrated safe in monkeys at doses 500 times higher than those that nearly proved fatal to the volunteers.

Following this trial, an assay using human cells was developed to predict immune system over-reactions, but the authors point out that the trial would never have taken place in the first place if the assay had been in use beforehand.

Now, the authors of the letter are calling on the UK Government to compare tests based on human biology with currently used testing methods to see which are more effective. A number of such tests have been proposed in the UK’s Safety of Medicines Bill 2010–11. The Bill does not propose any replacement of animal tests, merely their assessment of fit for purpose,” say the authors of the letter. “One hundred and forty eight Members of Parliament have already signed a motion in support of this proposal.”

“Some of us recently made representations to the UK Department of Health, and were told that the Government believes that human-biology-based systems have not been established as being more predictive than are animal studies for developing safer medicines,” say the authors. “We agree, but that is because no rigorous examination of such systems has been undertaken. The very purpose of the proposed comparison is to initiate such an examination, which is urgently necessary for the sake of the NHS, the pharmaceutical industry, and, most importantly, patients.”