[Clinical study of antalgic drugs]

The assessment of the clinical properties of analgesics is not easy. Some of the difficulties are due to the multiplicity of the aetiologies involved in the pain process, to the complexity of pathophysiological mechanisms modulating the nociception and to the subjectivity of painful sensation. All of these explain the fairly high variability of the criteria available for assessing pain level or pain relief. As a consequence, that variability directly interferes with the pharmacological effect of analgesics to be assessed in clinical trials. Furthermore, the lack of consensus concerning the evaluation criteria does not facilitate the choice of a study design or the comparison of data collected from different clinical trials. Clinicians have to choose between testing the analgesics in healthy volunteers (experimental pain) or in patients suffering from painful disease (spontaneous pain). These two approaches are often complementary for assessing the pharmacological profile of new analgesic compounds. Whatever the choice, the investigators have to pay attention to the methodological aspects to avoid pitfalls and bias in this difficult field of therapeutic research.