Sant Joan de Déu Barcelona - Hospital


There are many clinical trials that use the randomization technique in order to select what kind of treatment should be administered to the patient reagarding the research methodology ( in comparison to a placebo or another treatment).

Randomization is performed by a computer, not a medical professional, because this way it is easier to ensure equal opportunities for all participants to access the treatment and avoid any kind of bias.

Using this technique helps to confirm that any outcome from he trial is completely objective and that it not a reflection of the particularities of the participants.

Unless circumstances are excepcional, it is strictly forbidden to include a patient in a clinical trial without the previous signing of a document confirming his/her acceptance. This document is called informed consent and confirms that the participant or his/her legal representative have received the essential information relative to the study in order to decide to participate or not.

Informed consent is not a contract and it is possible to freely decide to abandon the clinical trial at any moment.

A blind or blinded-experiment is an experiment in which some information about the test is masked from the participants. These do not know if they are using the drug or a placebo. This methodology is employed in order to avoid any kind of bias until the trial has ended.

There are several anonymization methodologies for the information associated to a clinical trial:

  • When the patient is not aware of the treatment he/she is receiving: single-blind.
  • When both the patient and the doctor/tester do not know the treatment: double-blind.



Phase 4 is known as post-authorisation phase and it starts once the medicine is already in the market. Sanitary authorities require additional information from the pharmaceutical industry about the effects of the new drug in the “real world”. They also need to test the drug with more patients than those in Phase 3. 

At this stage, security and effectivity data are obtained with patient subgroups, comparing the effect of the drug in combination (or not) with other existing treatments.

This phase is iniciated once the security and effectivity results of the new drug are obtained from phases 1 and 2. The number of patients participating in phase 3 may range from 1,000 to 5,000. In phase 3 the drug is tested in relation to other existing treatments or to the placebo if there is no treatment.

The duration of phase 3 is superior to phase 2 and may last a year.

These kind of studies can be carried out simultaneously in different countries, thus, they are international studies in which different hospitals participate. 

In this phase patients participation is higher than in phase I (between 100 and 300).

The goal of this phase is to study the effectiveness of a drug in relation to the possible secondary effects and the appropriate dose for the patient. In paediatric patients, this will be performed according to the different age groups.

The aim of this phase is to study the security and toxicity of the new medicine. During this phase, the secondary effects that the drug may have on the health of the patient are considered (e.g. blood pressure rise).

The number of participants in this phase is small and in the case of adults these are all healthy volunteers. In paediatric clinical trials, however, phase 1 only includes patients because it is considered unethical to expose a healthy child to any drug. 

The number of patients in phase 1 range between 20-100.

Los ensayos clínicos son diseñados por profesionales médicos o de la salud. Para diseñar un ensayo clínico, es muy importante considerar iniciativas de investigación previas y ciertas cuestiones relacionadas con el tratamiento y los síntomas que precisan ser abordadas para que se de una mejora. Los aspectos éticos son también cruciales.

En el diseño de los ensayos clínicos hay diferentes participantes: médicos, enfermeras, pacientes, expertos en estadística y profesionales de apoyo, así como profesionales de la industria farmacéutica que colaboran para que el ensayo tenga el mejor diseño posible. El documento que recoge toda la información sobre el diseño del estudio se conoce como “protocolo”.

While clinical trials are generally research projects focused on the study of drugs, clinical research is a broader concept and it includes the study of medical devices (such as glucose meter), the evalution of a healthcare program or other iniciatives that are not directly linked to drugs. 

A clinical trial is a research project with human participation aimed to answer some specific questions about a new treatment (vaccines, new therapies or new indications of a known treatment).

Medical research projects help to determine whether a given treatment is safe and effective. Clinical trials are carried out in different phases. Each phase has a different purpose and seek different objectives (for example, toxicity, adequate dose, etc.).