Clinical trial phases

Clinical trials are tightly regulated by laws, which were made to protect participants, while ensuring that the drug in development will not be released for use as a patient treatment until it is safe and effective..

These trials are advanced in steps, each of which has to be successful in order to move on to the next phase - see phases I to IV below:

  • Phase I trials determine how safe a compound is in healthy volunteers (looking out for potential undesired side effects).
  • Phase II trials determine safety and the optimal dose in patients (the amount of the compound and how often it should be taken).
  • Phase III trials determine the compound’s effectiveness in patients.
  • Phase IV trials may be performed after the drug is already licensed and usually look for the effect of the drug outside the limited specifications of earlier clinical phase trials.

Each phase trial must show that it was successful in order to move on to the next phase trial.

Due to the complexity of these processes, it typically takes years from early development to marketing of a drug. In this process, many compounds fail to demonstrate effectiveness or for other reasons their development may be stopped.

More information on how drugs are developed may be found in EUPATI- European Patients' Academy

Drug compounds in development

Figure 1. Antibiotics (Drugs that are active against bacteria)

* Notes

Inhaled Amikacin (ALIS) - For infection with non-Tuberculous mycobacteria (NTM); marketed (USA) and ongoing
Inhaled Colistin - Marketed in some countries, other phase III studies ongoing
Aztreonam inhalation – Cayston - Completed study did not achieve predefined outcome; phase II to begin
Inhaled dual release Ciprofloxacin – Trials ongoing
Inhaled dry powder Tobramycin – Phase II completed

Figure 2. Drugs that target inflammation

* Notes

Inhaled A1AT – a protease inhibitor - A1AT- alpha 1 antitrypsin

Figure 3. Other drugs


Hypertonic saline - Use as physiotherapy adjunct
Inhaled mannitol - Phase III completed
ENaC inhibitor for patients with PCD (VX 371) – CLEAN-PCD - For PCD- Primary ciliary dyskinesia, a specific cause of bronchiectasis

How you could help

There are several ways you could get involved in research and clinical trials - see below - and also Get involved in research (scroll to the bottom of this page)

More information

Access the European Patient Ambassador Programme (EPAP) free, online module on 'Supporting research and development' to get more detailed information and knowledge about clinical trials, health research and getting involved.

The module is available in English, Dutch, French, German and Italian.

Register at