Alec B. O'Connor1 and Robert H. Dworkin2
1Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA departments of Anesthesiology and Neurology, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA
The World Health Organization defines a clinical trial as "any research study that prospectively assigns human participants or groups of humans to one or more health-related interventions to evaluate the effects on health outcomes" . This definition includes the double-blind, randomized clinical trial (RCT), considered the "gold standard" research design for clinical trials, as well as various prospective, uncontrolled, nonblinded cohort designs. In this chapter, we emphasize RCTs because uncontrolled trials produce treatment effect estimates that are substantially less informative than those from RCTs. Even among RCTs, however, study quality varies considerably, and many limitations and sources of bias can exist.
We focus on clinical trials of treatments for chronic pain, conventionally defined as pain that persists beyond 3 months or the normal time of healing . Chronic pain is typically classified based on its presumed etiology, specifically, neuropathic pain versus non-neuropathic inflammatory and musculoskeletal pain. Neuropathic pain is caused by a lesion or disease affecting somatosensory pathways of the peripheral or central nervous system , whereas non-neuropathic (i.e. nociceptive) pain reflects stimulation of specialized nociceptors in somatic tissue, with visceral pain often classified separately. We focus on trials of phar-macologic interventions for both of these types of chronic pain in this chapter, although many of the issues we address are also relevant to studies of psychologic therapies, nerve blocks, spinal cord stimulation,
Evidence-Based Chronic Pain Management. Edited by C. Stannard, E. Kalso and J. Ballantyne. © 2010 Blackwell Publishing.
physical therapy, acupuncture or any other procedure that can be used to treat chronic pain. We begin by reviewing the types of clinical trials and research designs that are most commonly used in investigations of chronic pain. Next, we discuss the major components of clinical trials, including the interventions studied, patient selection, and assessment of treatment outcomes. Finally, we discuss the analysis and interpretation of pain and related data in clinical trials, and conclude by summarizing the major sources of bias in clinical trials. Excellent resources are available for investigators undertaking clinical trials of pain treatments and for those who want additional information about the interpretation of clinical trials [4-10].
Clinical trials involve research on human subjects and it is therefore critical that all individuals involved in such studies become familiar with the ethical principles and obligations that apply to such research. This includes the roles and responsibilities of investigators conducting clinical trials, especially the importance of informed consent, and also applicable institutional, local, and national regulations and procedures for study review and approval. It is beyond the scope of this chapter to summarize these issues, particularly given geographic variation in specific considerations, but in-depth reviews are available .
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