Participation of Women in Clinical Trials of Drug Therapies: A Context for the Controversies

Marianne N. Prout, MD, MPH, Susan S. Fish, PharmD, MPH

Disclosures
In This Article

Conflicting Data on Women's Participation in Clinical Trials

The Institute of Medicine report clearly states: "Sex matters... "and "Barriers to the advancement of knowledge about sex differences in health and illness exist and must be eliminated." In the article, "The Men's Rights Movement Takes on the NIH," however, the author suggests that women are overrepresented in clinical trials.[4] These contrasting conclusions are rooted in the definitions and methods used in reviews of participation in research, particularly clinical trials. Reviews of the participation of women in clinical research have varied with the types of research studies included, the years of research publications included, and the outcomes used for comparisons by sex. Outcomes have included the total number of participants in all clinical trials by sex; the number of participants by sex only in non-sex-specific clinical trials, excluding the large trials that include only women; the percentage of clinical trials that exclude women; and the percentage of clinical trials that include sex-specific analyses. Not surprisingly, these reviews provide data for arguments on all sides of the debate.

A recent review by Meinert and colleagues[5] emphasizes that the percentage of female subjects (61%) in clinical trials exceeds that of male subjects. The methods used by this group include counting the number of participants in both sex-specific and non-sex-specific trials, limited to studies that include sex in the reported results, published in 5 journals in 1985, 1990, and 1995. By contrast, Vidaver and coworkers[6] emphasized the lack of analysis of data by sex, noting that two thirds to three fourths of National Institutes of Health (NIH)-funded studies published in 4 journals in 1993, 1995, 1997, and 1998 lacked sex-specific analyses. Harris and associates[7] looked at National Heart, Lung, and Blood Institute (NHLBI)-funded studies from 1965-1998 and reported that 54% of participants in all trials were female. However, when they excluded single-sex trials, the participants in the remaining non-sex-specific studies were only 38% female, reflecting the large contribution of participants by recent single-sex studies such as the Women's Health Initiative. In addition, Harris and colleagues expressed concern that women were underrepresented in studies of specific problems in cardiovascular disease.

Another approach to monitoring the participation of women is to count studies, rather than participants, as was done by McDermott and associates.[8] They examined the number of studies that excluded women from clinical research in 3 journals at 3 points in time and found that 11% of studies excluded women in 1971, 5% in 1981, and 3% in 1991. Bird[9] compared the ratio of the number of studies that excluded women to the number of studies that excluded men by study design on the basis of reports published in 1 journal in 1990 and 1992. For randomized controlled trials, 5 times as many studies excluded women as excluded men; for longitudinal studies, the ratio was 3.6; and for cross-sectional studies, the ratio was 0.8.

A comprehensive approach to monitoring inclusion in clinical trials of drug therapies entails compilation of a database of all US clinical trials that will incorporate studies by federal agencies, the pharmaceutical industry, and nonprofit organizations. Most of the currently available data on clinical trials participation by sex and race are NIH-funded studies; these data are summarized in Table 1.[10,11] NIH Phase 3 (extramural) clinical trial populations are predominantly female, reflecting the large Phase 3 trials specific to women now under way, whereas early-phase studies at NIH (intramural) include fewer women. The database will incorporate New Drug Application (NDA) protocols approved by the Food and Drug Administration (FDA) in the near future. Pilot data collected by the Center for Drug Evaluation and Research (CDER) of the FDA and from a member survey by the Pharmaceutical Research and Manufacturers of America (PhRMA) are also summarized in Table 1.[12,13]

The processes established to monitor the participation of women in clinical trials of drug therapies are impressive. A review of the history of women in clinical trials, however, is required to understand the attention now given to women's participation.

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