The procedures involved in clinical drug trials

Before human beings come into contact with a new drug, scientists test the drug for efficacy by performing statutory laboratory testing procedures on cell and tissue cultures and then on animals. Only if these tests produce promising results are researchers allowed to administer the active substance to human beings.

Media reports about promising results at this stage generally point out that the data has been obtained from animal experiments. However, successful trials on animals do not automatically mean that the active substance will receive drug approval. In many cases, researchers abandon drug development projects because tests on human beings do not produce the desired results or have too many negative side effects.

In this phase, scientists test the active substance on healthy volunteer probands. The purpose of the tests is to provide an indication of the tolerability and possible dosage range of the new drug. In addition, researchers investigate how the active substance is absorbed, distributed, degraded and excreted by the body.

In the case of particularly serious illnesses, such as AIDS or cancer, patients actually suffering from the disease also take part in these early experiments. The number of human beings treated with the drug in trial phases I and II is very low ─ only a few dozen.

In the second phase of a trial, the active substance is administered to patients suffering from the disease in order to test the efficacy of the drug. In these tests, researchers also identify the most appropriate and tolerable dose. Particular attention is paid to homogeneity within the patient group. Therefore, trial participants have to be very carefully selected in this phase.

Media reports about results in the second phase of a trial often speak of successful tests on a “limited number of patients”. It takes several more years for the new drug to be approved. This is because the lengthiest and most complicated part of the clinical testing procedure is still to come: trial phase III.

Phase III is the final stage of the trial before approval of the new drug. In this phase of the trial, scientists administer a particular dose of the active substance to hundreds of patients. In order to reflect the wide range of patients seen in routine clinical practice as realistically as possible, the participants in this phase are not selected on the basis of strict criteria.

Drugs intended for use over a long period of time are tested in corresponding long-term trials, which are designed to ensure that the active substance remains effective and tolerable even after prolonged use.

Patients who are not satisfied with the medication they have received so far can be given the new active substance within the context of a clinical trial. All patients must comply with the inclusion criteria and receive treatment at a practice participating in the trial.

Promising test results in phase III are the prerequisite for approval of a new drug therapy. The authorities responsible therefore check the drug registration application and the corresponding data very carefully, which is a time-consuming process.

In this final pre-approval phase, more frequent reports about the drug appear in the media owing to the increased information available. By this time, specialist physicians have already had some experience of treating patients with the drug over the course of the trial. Furthermore, papers about the active substance are published in professional journals and at medical congresses.

Following approval of the drug, phase IV trials are intended to provide information about its use on a routine basis. The aim is to find out more about rare negative side effects and the efficacy of the drug in particular patient groups.