Before a new drug is approved and can be taken to the market, two stages are distinguished:
- a preclinical phase, which includes laboratory studies and animal studies
- a clinical phase, in which clinical studies are conducted in humans
The first phase takes place in a laboratory. Of all the substances that are tested in a laboratory during these early phases, very few will pass to a phase where the substance is tested in humans. Preclinical studies include:
- Cellular studies: these are the first tests performed to study the efficacy of a new treatment. Researchers analyse the effects of the new treatment on cells that have been grown on a laboratory plate or in a test tube.
- Animal studies: treatments that seem promising based on cellular studies are tested on live animals. This gives researchers an idea of the behaviour of the new treatment in a living being.
Preclinical studies provide very useful but insufficient information on the safety and efficacy of the drug, after all, humans and animals are different. A drug that works in animals may not work in humans or there may be side effects and other problems that do not occur in animals but may occur in humans. Therefore, if the preclinical results are promising, and after reviewing all the information provided by the researchers, the Regulatory Bodies will grant an authorisation for the new drug to be tested in humans in a clinical study.
Within the clinical studies, a series of phases must also be overcome before the final authorisation for commercialisation of the drug can be given. Each one is designed to answer certain questions and ensure the safety of the participants.
Phase I studies are clinical trials where a new drug is administered to humans for the first time. Participants in this phase are usually a small group of healthy volunteers (from 20 to 80 individuals). The objective of the study is to evaluate the safety of the drug, to detect and identify possible incipient signs of toxicity and side effects, how the drug is distributed by the body, and establish the best form of dispensing and dosage.
In this phase, the drug is administered to people who have the disease which it has been developed for. The total number of patients is still small (several hundreds of people). The purpose of a Phase II study is to know more about the therapeutic efficacy/toxicity relationship, as well as to establish the optimal dose or the maximum doses of the drug.
Phase III is the most advanced phase before taking the drug to the market. The number of patients in these studies is larger (from several hundred to several thousand, depending on the pathology) and the purpose is to evaluate the efficacy and safety of the drug. When the Phase III studies have been completed and the promoter of the drug has demonstrated that the medication is safe and effective under certain conditions, the Health Administration can approve its release to the market.
Phase IV studies are conducted when the drug is already in the market. They are important to collect additional information on the long-term safety and efficacy of the drug in real-life conditions, to find possible interactions with other treatments or concomitant diseases or to study new indications.