Efficacy dilution in randomized placebo-controlled vaginal microbicide trials

Statistical Center for HIV/AIDS Research & Prevention, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA.
Emerging Themes in Epidemiology (Impact Factor: 2.59). 10/2009; 6(1):5. DOI: 10.1186/1742-7622-6-5
Source: PubMed


To date different vaginal gel microbicides have been evaluated in phase 2b/3 trials, but none have demonstrated effectiveness for preventing HIV infection. Failure to demonstrate effectiveness however does not necessarily indicate that a product is truly inefficacious, as several sources of efficacy dilution may compromise our ability to identify products that may have been truly efficacious.
For four individual sources of dilution, we describe the dilution mechanisms and quantify the expected effectiveness. An overall expected effectiveness that combines all sources of dilution in a trial is derived as well.
Under conditions that have been observed in recent microbicide trials, the overall expected effectiveness assuming an active gel with true efficacy of 50% and 75% are in the range of [16%; 33%] and [28%; 50%], respectively, when considering the four major sources of dilution. In contrast the diluting effect due to adherence alone (assuming an adherence of 80%) leads to higher expected effectiveness, 40% and 60% assuming an active gel with true efficacy of 50% and 75%, respectively. Individual sources of dilution may demonstrate a small effect when evaluated independently, but the overall dilution effect in a trial with several sources of dilution can be quite substantial.
Currently planned phase 2b/3 microbicide trials of new candidate vaginal microbicides are not immune from these shortcomings. A good understanding of dilution effects is necessary to properly interpret microbicide trial results and to identify products worthy of further development and evaluation. Greater attention should be devoted to reducing and assessing the impact of efficacy dilution and to carefully selecting the effect size in the design of future trials.

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Available from: Benoît R Mâsse
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    • "Adherence has emerged as a particularly critical issue for clinical trials of user-dependent technologies such as Pre Exposure Prophylaxis (PrEP), delivered as tablets or vaginal gels [1-3]. Understanding what shapes adherence to investigational products has therefore generated much attention in the recent literature [4]. "
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    ABSTRACT: Background Although significant progress has been made in clinical trials of women-controlled methods of HIV prevention such as microbicides and Pre-exposure Prophylaxis (PrEP), low adherence to experimental study products remains a major obstacle to being able to establish their efficacy in preventing HIV infection. One factor that influences adherence is the ability of trial participants to attend regular clinic visits at which trial products are dispensed, adherence counseling is administered, and participant safety is monitored. We conducted a qualitative study of the social contextual factors that influenced adherence in the VOICE (MTN-003) trial in Johannesburg, South Africa, focusing on study participation in general, and study visits in particular. Methods The research used qualitative methodologies, including in-depth interviews (IDI), serial ethnographic interviews (EI), and focus group discussions (FGD) among a random sub-sample of 102 female trial participants, 18 to 40 years of age. A socio-ecological framework that explored those factors that shaped trial participation and adherence to study products, guided the analysis. Key codes were developed to standardize subsequent coding and a node search was used to identify texts relating to obstacles to visit adherence. Our analysis includes coded transcripts from seven FGD (N = 40), 41 IDI, and 64 serial EI (N = 21 women). Results Women’s kinship, social, and economic roles shaped their ability to participate in the clinical trial. Although participants expressed strong commitments to attend study visits, clinic visit schedules and lengthy waiting times interfered with their multiple obligations as care givers, wage earners, housekeepers, and students. Conclusions The research findings highlight the importance of the social context in shaping participation in HIV prevention trials, beyond focusing solely on individual characteristics. This points to the need to focus interventions to improve visit attendance by promoting a culture of active and engaged participation.
    Full-text · Article · Jul 2014 · BMC Women's Health
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    • "Difficulties in measuring adherence in microbicide trials have been widely observed and well-documented [3–7]. Adherence is framed, defined and measured almost exclusively as a modifier of product efficacy [8,9]. The search for an objective measure of adherence as an effect modifier is constrained by the limitations of self-report and biological markers. "
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    ABSTRACT: After two decades of microbicide clinical trials it remains uncertain if vaginally- delivered products will be clearly shown to reduce the risk of HIV infection in women and girls. Furthermore, a microbicide product with demonstrated clinical efficacy must be used correctly and consistently if it is to prevent infection. Information on adherence that can be gleaned from microbicide trials is relevant for future microbicide safety and efficacy trials, pre-licensure implementation trials, Phase IV post-marketing research, and microbicide introduction and delivery. Drawing primarily from data and experience that has emerged from the large-scale microbicide efficacy trials completed to-date, the paper identifies six broad areas of adherence lessons learned: (1) Adherence measurement in clinical trials, (2) Comprehension of use instructions/Instructions for use, (3) Unknown efficacy and its effect on adherence/Messages regarding effectiveness, (4) Partner influence on use, (5) Retention and continuation and (6) Generalizability of trial participants' adherence behavior. Each is discussed, with examples provided from microbicide trials. For each of these adherence topics, recommendations are provided for using trial findings to prepare for future microbicide safety and efficacy trials, Phase IV post-marketing research, and microbicide introduction and delivery programs.
    Full-text · Article · Apr 2013 · Journal of the International AIDS Society
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    • "Effectiveness peaked at 54% in women who reported using the microbicide in at least 80% of sex acts [12]. Adherence to microbicides is critical in terms of detecting an effect in clinical trials and reducing the risk of HIV acquisition when an effective microbicide is available [14]. "
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    ABSTRACT: A safe and effective vaginal microbicide could substantially reduce HIV acquisition for women. Consistent gel use is, however, of great importance to ensure continued protection against HIV infection, even with a safe and effective microbicide. We assessed the long-term correlates of consistent gel use in the MDP 301 clinical trial among HIV-negative women in sero-discordant couples in south-west Uganda. HIV-negative women living with an HIV-infected partner were enrolled between 2005 and 2008, in a three-arm phase III microbicide trial and randomized to 2% PRO2000, 0.5% PRO2000 or placebo gel arms. Follow-up visits continued up to September 2009. The 2% arm was stopped early due to futility and the 229 women enrolled in this arm were excluded from this analysis. Data were analyzed on 544 women on the 0.5% and placebo arms who completed at least 52 weeks of follow-up, sero-converted or became pregnant before 52 weeks. Consistent gel use was defined as satisfying all of the following three conditions: (i) reported gel use at the last sex act for at least 92% of the 26 scheduled visits or at least 92% of the visits attended if fewer than 26; (ii) at least one used applicator returned for each visit for which gel use was reported at the last sex act; (iii) attended at least 13 visits (unless the woman sero-converted or became pregnant during follow-up). Logistic regression models were fitted to investigate factors associated with consistent gel use. Of the 544 women, 473 (86.9%) were followed for at least 52 weeks, 29 (5.3%) sero-converted and 42 (7.7%) became pregnant before their week 52 visit. Consistent gel use was reported by 67.8%. Women aged 25 to 34 years and those aged 35 years or older were both more than twice as likely to have reported consistently using gel compared to women aged 17 to 24 years. Living in a household with three or more rooms used for sleeping compared to one room was associated with a twofold increase in consistent gel use. In rural Uganda younger women and women in houses with less space are likely to require additional support to achieve consistent microbicide gel use. Trial registration Protocol Number ISRCTN64716212
    Full-text · Article · Feb 2013 · Trials
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