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The intermittent PrEP is more likely to be effective in anal sex than vaginal sex

Pharmacodynamic studies reflect the PrEP drug concentrations are affected not only before the rectum of the vagina, but also is also highest.

pharmaceutical production line at factoryThe results of a study analyzing the pharmacodynamics of tenofovir and emtricitabine (the two drugs that make up Truvada, the only drug approved for use as a prophylaxis before [PrEP]) allow you to determine the effectiveness of intermittent PrEP may be higher than initially thought, at least in terms of anal sex. However, the development of drug concentrations in the vagina and uterus makes this strategy may not be as secure in the case of vaginal intercourse at least with these drugs. These data were presented at the Eighth International AIDS Society Conference on Pathogenesis, Treatment and prevention of HIV / AIDS (IAS 2015), being held this week in the Canadian city of Vancouver.

One of the studies that received great attention was the so-called ADAPT, among the main conclusions was that the people participating adhered more easily to a daily pattern of PrEP than a more spaced or based on the anticipation of sexual intercourse. Despite all this, the Ipergay study (which is evidenced by an intermittent PrEP regimen) showed an efficiency of 86%, the same efficacy as that of the PROUD study, which is evidenced by daily administration (see news item 30 / 10 / 2014.E and 22 / 10 / 2014.). The good results of the study on intermittent PrEP raises the question of how far doses can be spaced to ensure they remain effective. In this regard, several studies have examined the rates of absorption and elimination of medicinal products included in Truvada® as well as their concentrations in the rectum and vagina.

IAS

In an Ipergay sub-study, volunteers received a double dose of Truvada® and blood levels of the drug were checked before the 1 dose, and thereafter: 0,5 and 1; 2; 4; 8 and 24 hours after its administration, also having samples of secretions and rectal biopsy at this time. 30 minutes after administration of the double dose protective levels of rectal emtricitabine in secretions were available, whereas it took 24 hours to detect adequate levels of tenofovir. This may mean that when you start PrEP, the first protection against HIV comes only from emtricitabine. The increase in concentration in rectal biopsy was achieved by the double dose was only 40%, which in the opinion of the study authors reflects that if you take the intermittent Prep, it is extremely necessary to take the subsequent doses after intercourse sexual relations.

laco - AIDS-bigThe conference also presented another study on the pharmacodynamics of tenofovir and emtricitabine in 19 volunteers (men and women) without HIV infection. Data showed that peak levels of tenofovir in cervical tissue (cervix) were much lower than those detected in rectal tissue (about 10% at best). Furthermore, the time it reached the highest levels was much greater in the cervical (10 the 12 days) than the straight (about 5 days).

In the present study, it was estimated that the protection of an anal after a single dose of tenofovir was 77%. Although the results in this are much larger than 38% observed previously in a study of rectal tissue samples must be remembered that the confidence interval in the recent study is very wide and, in fact, the lower limit is 40% , a value that is more similar to that mentioned above.

The protection would be estimated at 89% after two doses and 98% after three doses. Indeed, in a substudy of iPrEx (one of the trials, which was a survey to Truvada base as prophylaxis before the US), they had concluded that taking four doses a week could be enough to get an almost Protection 100% (see La noticia del dia 21 / 03 / 2012). With regard to the discontinuation of PrEP after using it on a daily basis for 30 days, the protection against HIV in anal intercourse would be 97%, 24 hours, 96% in 3 days, 93% in five days or until even 90% a week without taking the medication.

3d red blood cellsHowever, no one knows for sure how they would develop this level of protection to the beginning and end of PrEP in the event of exposure to HIV vaginally. This means that there is insufficient data to determine the extent to which intermittent PrEP could also be an option in the case of vaginal sex, because today is still recommended that the strategy in this case is the daily dose.

The results presented suggest that, in the case of anal sex, PrEP (when taken consistently for a time) offers protection that lasts up to one week after discontinuation, and that Truvada® should be taken again within this time interval; There is an increase in protective levels of emtricitabine within a matter of hours. However, there is a need to clarify whether PrEP is still effective if taken before intercourse after the time interval has elapsed, and it is also very important to know whether it is necessary to take the two subsequent doses to intercourse.

Despite these results, the World Health Organization will likely recommend a daily dose of PrEP as the best option for your next guidelines, hoping to get more data on this. In any event, although not affect the guidance, it is very important to determine the safety limits of intermittent making PrEP, since it is very likely that many people do the maintenance of a perfect adhesion daily.

Miguel Vázquez - 23 / 07 / 2015 Translated from Spanish into original in IAS 2015: La intermittent PrEP tiene más Outlook On being effective en el anal sex than vaginal en el by Claudio Souza. reviewed by Mara Macedo

Source: Aidsmap/ Prepared by (GTT HIV-)

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