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Tenofovir Gel

Tenofovir Gel

Tenofovir Gel for Preventing HSV-2 Infection?

In a study involving women in South Africa, pericoital application of tenofovir gel halved the risk for acquiring herpes simplex virus type 2.

Herpes simplex virus type 2 (HSV-2) infection is among the most common sexually transmitted diseases worldwide. Tenofovir, a nucleotide reverse-transcriptase inhibitor used in tablet form for treating HIV infection, also has activity against HSV-2. In the VOICE trial (results recently reported but not yet published), tenofovir gel reduced the risk for acquiring HSV-2 by 46%. To further evaluate its efficacy in preventing HSV-2 infection, investigators conducted a subgroup analysis involving 422 HSV-2–negative women enrolled in CAPRISA 004, a double-blind, placebo-controlled, randomized trial conducted in South Africa to assess whether tenofovir gel prevents HIV transmission to women.

Tenofovir and placebo gels were dispensed in prefilled vaginal applicators with instructions to use one dose within 12 hours before sex and a second dose as soon as possible within 12 hours after sex, with a maximum of two doses per 24-hour period. Mean follow-up duration was 18 months, and study retention was 94.8%. HSV-2 seroconversion was detected by enzyme-linked immunosorbent assay, with Western blot testing performed for verification.

The overall incidence rate of HSV-2 infection was 10.2 cases per 100 person-years (95% confidence interval, 6.8–14.7) for the tenofovir gel group versus 21.0 cases per 100 person-years (95% CI, 16.0–27.2) for the placebo group (incidence rate ratio, 0.49; 95% CI, 0.30–0.77). HSV-2 infection was confirmed by Western blot testing in 51 (59%) of the 87 women with seroconversion; the incidence rate ratio in this group was 0.45 (95% CI, 0.23–0.82)

Genital inflammation reduces efficacy of tenofovir gel

Why do some women get HIV infection, even though they are using tenofovir gel for prophylaxis? A new study by scientists at the Centre for the AIDS Programme in Research in South Africa (CAPRISA) and Columbia University's Mailman School of Public Health, shows that genital inflammation significantly reduces the effectiveness of tenofovir gel in preventing HIV infection in women.

These findings indicate that both genital inflammation and adherence need to be addressed to improve the effectiveness of topical pre-exposure prophylaxis strategies for HIV prevention in women. The findings are published online in Nature Medicine.

The researchers measured small proteins, known as cytokines, in the vagina. Raised cytokines levels in the vagina indicate the presence of inflammatory immune responses, even in the absence of clinical symptoms.

HIV infection rates and cytokine levels as a marker of genital inflammation were studied in 774 women over 2.5 years. The researchers found that women with genital inflammation were at higher risk of subsequently contracting HIV compared to women without inflammation. The study further showed that tenofovir gel provided 57 percent protection against HIV acquisition in women who had no evidence of vaginal inflammation but provided no protection in women with genital inflammation, even if they used the gel consistently.

"This study gives us an important clue to enhance HIV prevention in women. It is not only adherence-related behaviours, but also biological processes in the vaginal that need to be addressed to prevent HIV and enhance the effectiveness of topical PrEP," said Salim Abdool Karim, PhD, director of CAPRISA and professor of Epidemiology at the Mailman School of Public Health at Columbia.

In the study, 9 pro-inflammatory cytokines were measured in specimens collected at over 2,139 clinic visits at a rural and urban clinic in KwaZulu-Natal, South Africa to define the levels of genital inflammation. In women who had no genital inflammation, women assigned to tenofovir gel had a HIV incidence rate of 2.3 per 100 person-years, compared to 5.4 per 100 person-years in women assigned to placebo gel. Conversely, in women with genital inflammation, the HIV incidence rate in those assigned to tenofovir gel was 6.8 per 100 person-years compared to 7.0 per 100 person-years in women assigned to placebo gel

The study found that among women who used the gel most of the time (> 50% of sex acts), tenofovir gel was 75 percent protective in those women who had no genital inflammation as compared to no protection in women with evidence of genital inflammation.

In 2010, the CAPRISA 004 trial provided the first evidence that tenofovir can prevent sexual transmission of HIV. Tenofovir gel reduced HIV acquisition by 39 percent overall. Two subsequent studies found that tenofovir gel was not effective, most likely because most of the women in the trials did not use the gel consistently. A sub-group analysis of the FACTS001 and the MTN 003 trials showed that the gel was just over 50 percent effective in consistent users, highlighting the importance of high adherence. The new evidence emerging from this genital inflammation study indicates that there may be a biological basis for the differing results as well.

The causes of genital inflammation are not well understood at present. Previous studies have shown that there are many possible causes of genital inflammation in women, including imbalances in the bacteria of the vaginal microbiome, sexually transmitted infections and vaginal practices.

Tenofovir Gel May Prevent Herpes Simplex Virus in Women

In the study, 1,004 women across Uganda, South Africa, and Zimbabwe were instructed to apply the vaginal gel containing tenofovir (1%) on a daily basis to prevent HIV. Tenofovir is one component of the combination pill Truvada, used in HIV pre-exposure prophylaxis (PrEP). Because adherence to prevention regimens affects outcomes, the researchers in this study measured tenofovir levels in biologic samples (blood samples and vaginal swabs) to know for sure which women were actually using the medication.

They then compared the incidence rate of new HSV-2 infections between women with evidence of tenofovir in their system and women without tenofovir in their system.

Researchers measured levels of tenofovir in the blood after three months and from a vaginal swab after six months. At the beginning of the study, 56% of the original sample (a total of 532 women) were susceptible to HSV-2 infection (i.e., were HSV-2 negative).

three months, there were a total of 92 new HSV-2 infections. Fifteen new infections were in women who had a detectable level of tenofovir in their blood, while 77 were among women who were not using the tenofovir gel.

A difference in HSV-2 risk between women using and not using the medication was evident. Only about a quarter of women with access to the tenofovir gel had detectable tenofovir levels after three months. Women with detectable tenofovir in their blood after three months were about half as likely to acquire HSV-2 over time.

Marrazzo noted that her team controlled for a number of factors that could be associated with adherence, but that the relationship was still evident even after adjusting for things like age, marital status, having more than two partners, anal sex, HIV status, and hormonal contraceptive use. This finding points to the robustness of the study’s findings.

At the six month time point, Marrazzo’s team found a similar trend using vaginal swab samples to measure medication use. Close to 50% of the women with access to the tenofovir gel had detectable tenofovir levels.

Among the 89 new HSV-2 infections, 32 came from women with detectable tenofovir levels and 57 came from women without detectable tenofovir levels. Although there was a higher incidence rate of tenofovir-users compared to non-users (19.7 versus 14.1) this difference didn’t reach statistical significance.

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