As few as two PrEP pills a week protect during anal sex
A comparison between the people allocated to oral PrEP in the two pivotal studies that compared it to injectable PrEP, HPTN 083 and HPTN 084, has found that the pills provided 99% protection against HIV infection to the gay and bisexual men and transgender women in HPTN 083 as long as they consistently took two or more pills a week. But the cisgender African women in HPTN 084 had to maintain daily PrEP – all seven pills a week – to receive the same efficacy.To get more news about http://www.vigrxplus-original.....com/VigRX-Oil-Male-E vigrx oil prices, you can visit vigrxplus-original.com official website.
The study also found that adherence to oral PrEP in the women taking part in HPTN 084 was considerably lower than in the participants in HPTN 083, thus reducing its efficacy even further. This contributed to the fact that while injectable cabotegravir was 66% more effective than oral PrEP in the latter study, it was 91% more effective in the former.
The study by Professors Peter Anderson, Mark Marzinke and David Glidden is the latest study to find that the antiretroviral drug tenofovir takes longer to reach effective concentrations in vaginal tissue cells than it does in rectal tissue cells, and may never reach such completely protective levels.
Tenofovir can be given as two different prodrugs – tenofovir disoproxil (TDF) and tenofovir alafenamide (TAF) but gets turned into the active drug inside cells. The HPTN studies used TDF, and we still don’t have data on TAF’s efficacy as PrEP in women.
The second drug in oral PrEP can be either emtricitabine (FTC) or lamivudine (3TC). Both contribute importantly to efficacy, especially in women; but they do not persist so long in cells, so tenofovir levels are a better guide to adherence and its relationship to efficacy.
In both studies, blood plasma drug levels were measured in samples taken at every two-monthly clinic visit, and levels inside red blood cells were measured in dried blood spot (DBS) samples taken every third clinic visit, i.e. every six months. Blood plasma levels reveal drug levels in the week before the sample is taken, whereas DBS levels reveal average adherence levels over a period of months.
The protective levels of efficacy were derived by looking at the blood plasma levels of drug taken at the visit when the person tested HIV-positive and also at the visit before that. These were correlated with DBS levels. Blood plasma levels usually correlate broadly with the longer-term patterns of adherence revealed in the DBS samples. If they don’t – for instance if a high blood plasma level of drug is seen despite low DBS levels – then this suggests that the person has only taken a dose or two of PrEP before coming to the clinic (so-called ‘white coat dosing’).
There were 39 infections on TDF/FTC versus 12 on injectable cabotegravir in HPTN 083, and 36 versus three in HPTN 084. Evidence of white-coat dosing was seen in eight cases (25%) in HPTN 084, but only three (8%) in HPTN 083.
Average long-term levels of adherence were estimated by looking at the DBS levels in all participants taking oral PrEP who acquired HIV. Although the evidence linking levels in red blood cells with frequency of dosing comes from studies in gay men, there is no reason to think they differ in women. Levels of over 1250 femtomols in each sample indicated daily dosing, 700-1250 4-6 doses a week, 350-700 2-4 doses a week, and below 350 but detectable, 0-2 doses a week. (A femtomol is a trillionth of a mole, but 350 femtomols still means 2100 trillion individual tenofovir molecules per sample.)
