Outcome measurement in female sexual dysfunction clinical trials: review and recommendations

Defining and measuring Female Sexual Dysfunction (FSD) is a complex and challenging task. Several factors have confounded the theory and measurement of FSD including: the use of an inappropriate male paradigm; difficulty in capturing the complexity of women's sexual response; an evolving but presently untested nosology; and the relative independence between subjective and objective aspects of women's sexual response. Each of these factors have contributed to the difficulty in developing meaningful and valid endpoints for clinical trials. The Food and Drug Administration's (FDA) 2000 draft guidance document for female sexual dysfunction clinical trials recommended the use of daily diary measures as primary and self-administered questionnaires (SAQs) as secondary endpoints. Event logs or diary measures may be adequate for assessing aspects of male sexual performance (e.g., erectile function), or in other therapeutic areas with discrete and readily observable endpoints (e.g., incontinence). However, psychometric theory suggests that for female sexual dysfunction clinical trials, SAQ instruments may provide more sensitive and reliable measures of outcome. We offer an alternative set of recommendations in the hope that the FDA will reconsider its position and to serve as potential guidelines for non-industry sponsored research on female sexuality as well. First, we propose that SAQs be elevated from their current status as secondary endpoints to be considered as potential primary endpoints in clinical trials of FSD. Second, we recommend that depending on the trial design and intervention under study, either an SAQ or diary measure (typically one or the other, and not both), might serve as a primary endpoint in a clinical trial. Third, SAQs and diaries should be employed, analyzed and interpreted in their particular areas of strength. Diaries are most useful for enumerating events and/or counting frequencies. SAQs are superior at gathering subjective data related to women's sexual function. Fourth, we believe there is a theoretical basis for considering SAQs to be superior measurement tools compared to diaries in assessing sexual dysfunction in women. At present, however there is insufficient objective data to fully support this opinion. Conversely, we do not anticipate either theoretical or objective evidence to support the alternative hypothesis (that diaries are superior to SAQs). If this proves to be correct in the future, diary measures may no longer be considered as primary endpoints for FSD clinical trials. Finally, we recommend that the FDA and/or other regulatory agencies reconsider the emphasis given to the number of successful or satisfactory sexual events over time as primary endpoints because they do not definitively demonstrate whether there has or has not been any improvement in the FSD endpoint under study (e.g., sexual desire). Successful and satisfactory encounters represent an amalgam of subjective assessments that are too far removed from the essential FSD component.