Mice, the unsung heroes of medical breakthroughs

Many treatments would not exist if they were not tested on these rodents, which are essential for research because of their low cost and rapid life cycle.

It is not uncommon to find headlines of this kind in mainstream media: "For the first time: the regression of pancreatic cancer" or "Genetic editing can prevent liver disease". In these two examples, as in many others, two very important words are missing, the absence of which deceives the reader: "in mice". Numerous investigations made with these rodents – which are essential for medicine – yield encouraging results for the cure of various diseases, but only a small percentage of the solutions found in experimentation with these animals reach clinical practice with humans.

The scientific community has already echoed on social media the distance 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 advances that are still in the preclinical phase. It is necessary to alert citizens to sensationalism in medical information and to make them aware of how long and hard the path of biomedical research is.

Phases of clinical trials

It is significant to disclose how clinical trials, which consist of several phases, are carried out. The first is the so-called preclinical, in which the efficacy and safety of a drug is tested before it is tested in humans. It is conducted with animals, especially with mice.

Why mice? Experts cite several reasons, to begin with, an ethical one: we prefer 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, scientists explain that testing medicines on primates close to our lineage would not ensure that the results would be more conclusive to humans. Even so, treatments are tested whenever possible in in vitro cultures. This method allows to study 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 concrete 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 is very fast. The latter is very important, because it facilitates the monitoring of the effect of a drug on these rodents, the different stages that such a process goes through.

Studies with patients

At the end of the preclinical stage, the study of the therapy in question is carried out in patients: phase one. The primary objective here is to know if the drug is safe and in which dose, and the best way to administer it is studied. In this step there are usually very few participants. In phase two the safety of the therapeutic molecule is still tested and its efficacy is analysed. More participants are joined in order to obtain a meaningful sample to demonstrate whether the drug works or not. The last stage before a new drug goes into clinical practice is phase three, where the effects of the drug are studied in a very large number of participants and, in many cases, its effectiveness is compared with that of other drugs developed for the same health problems.

At the end of this stage, the companies or laboratories producing the study submit the final data to the regulatory agencies, which, depending on them, either authorise the marketing of the active substance or do not specify its uses. Phase four of the trial, which monitors the efficacy of the drug, starts with the treatment already in use, if there are any adverse effects or if there are any additional benefits not foreseen in the previous phases.

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