It is not uncommon to find headlines of this type in generalist media: “Pancreatic cancer disappears for the first time.” Or “Gene editing can prevent liver disease.” Both these two examples and many others are missing two very important words, the absence of which misleads the reader: “in mice.” Numerous investigations carried out with these rodents – essential for medicine – show encouraging results for the cure of various diseases , but only a low percentage of the solutions found in experimentation with these animals reach clinical practice with people.
The scientific community has already echoed on social networks the distance that goes from successfully testing a treatment in rodents to getting it to work in humans. On Twitter, the hashtag #inmice (in mice) brings together news about all these developments that are still in the preclinical phase. It is necessary to alert citizens to the sensationalism in medical information and to make them aware of how long and hard the path of biomedical research is.
Phases of clinical trials
In this sense, it is very important to disclose how clinical trials are carried out, which have several phases. The first is the so-called preclinical, in which the efficacy and safety of a drug are tested before testing it in humans. It is done with animals, especially mice.
But why in them? Experts allege several reasons. To begin with, an ethical one: it is preferred to work with species that are considered less close to human beings, not so evolved, at least as far as the nervous system is concerned. In addition, the scientists explain that testing the drugs in primates close to our lineage would not ensure that the results were more transferable to people. Still, treatments are tested whenever possible in in vitro cultures. This method allows studying the mechanisms of action of different drugs, but there are fundamental results that cannot be obtained if the tests are not transferred to animal models. This happens because it is in a complex cellular environment where more specific aspects of the functioning of medicines can be observed.
Two other reasons explain the massive use of mice: their economic cost is very low, and their life cycle very fast. The latter matters a lot, because it facilitates the monitoring of the effect of a drug in these rodents, the different phases through which this process passes. In light of all this, it is understood that the Confederation of Scientific Societies of Spain issued a statement in 2015 in which it stated that laboratory experiments with animals are essential for the advancement of science.
Study in patients
After the preclinical stage, the study of the therapy in question in patients is passed: phase 1. The main objective here is to know if the drug is safe and in what dose, and the best way to administer it is studied. There are usually very few participants in this step. In phase 2 the safety of the therapeutic molecule continues to be tested and its efficacy is analyzed. More participants are recruited, in order to obtain a meaningful sample that demonstrates whether or not the drug works. The last stage before a new drug enters clinical practice is phase 3, where its effects are studied in a very large number of participants and, in many cases, its efficacy is compared with that of other drugs developed for the same health problems.
After this stage, the companies or laboratories that prepare the study present the final data to the regulatory agencies, which, based on these, authorize or not the commercialization of the active principle and specify its uses. With the treatment already in application, phase 4 of the trial begins, which monitors the efficacy of the drug, if there are adverse effects or if any other additional benefit is found that had not been foreseen in the previous phases.
By Nieves Sebastián
