Open Clinical Trials

An open clinical trial (CT) may have two different meanings based on the possibility of modifying the characteristics described in the study protocol or on the level of masking of the treatment or intervention administered.

1. Based on the Possibility of Modifying the Characteristics Described in the Study Protocol:

• A clinical trial is open if its characteristics can be amended during its course in order to solve possible unexpected events. These changes to the study initial characteristics are more common in Phases I and II, in which case the results obtained are less conclusive.
• A clinical trial is closed if the initial characteristics of its protocol cannot be amended. This design is commonly used when research is conducted at several simultaneous sites (multicenter trials). If characteristics changed, the results from the different sites could not be evaluated together. An open clinical trial can also refer to uncontrolled or non-masked (non-blinded) clinical trials, and therefore it is not a very accurate term.

1. Based on the Level of Masking:

• A trial is open or open label when the patient knows if he/she has been assigned to the experimental or control treatment arm.
• A single-blind study means the patient does not know if he/she has been assigned to the experimental or control treatment arm. When neither the patient nor the investigator is aware of patients' treatment assignment, it is a double-blind If patients' assignment to the experimental or control treatment arms is also concealed from the people who analyze the data, then it is a triple-blind CT.

The most desirable option is almost always a single-blind CT. A double-blind or triple-blind design is preferable when the variables to be measured by investigators may have a subjective component. When conducting a blind clinical trial, treatments need to be masked, i.e., they must have a similar appearance and administration in a way that patients don't know which treatment they are receiving.

Non-blinded studies may be of interest for two main reasons:

• It's easier to conduct a non-blinded study than a blind study.
• Investigators may feel more comfortable to make decisions if they know the patient's assignment to a treatment or intervention, but these studies present certain disadvantages, the most significant of which is the possibility of bias.

From a psychological perspective, patients' knowledge of the treatment assigned may be beneficial. However, if they know they are receiving active treatment or placebo, based on the study design they may have an unfavorable reaction since they may feel that they are not getting the best treatment even though the new drug is still under study. All this may have an impact not only on patients' cooperation during the study but also on their treatment response.