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7/23/2019 10:41 PM

Event Driven PrEP: Science and the Prévenir Study

Another presentation on PrEP at IAS-2019 in Mexico City, by Jen-Michel Molina from Paris, included a report that no participants in the French Prévenir study who consistently used either Daily or On-demand PrEP have acquired HIV.

Event-driven PrEP involves taking a double dose (two pills) of tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) from 2-24 hours before sex is anticipated, and then, if sex occurs, one pill 24 hours after the double dose and another single pill 24 hours later. If sex occurs several days in a row, one pill should be taken each day, until 48 hours after the last event.

As of early May 2019, Prévenir had enrolled 3057 men at 26 sites, exceeding the original target. Almost all were men who have sex with men, and 30 self-identified as heterosexuals and 13 transgender people were also included. Most (85%) were white and the median age was 36. Over half the participants did not have a regular sexual partner. They had a median of 10 sexual partners during the past three months and a median of two acts of condomless sex in the past month. “Chemsex,” or use of recreational drugs when they last had sex, was reported by 14%.

About half the men opted for event-driven PrEP, and this proportion remained consistent over 18 months of follow-up. About 15% switched regimens, with an equal number changing from daily to intermittent and from intermittent to daily dosing. Almost all men (97%) in the daily PrEP arm, but only 82% in the event-driven arm, said they had taken PrEP as directed the last time they had sex. The most common reason for not taking PrEP was feeling like the sex was low risk. About 20% in both groups reported using condoms when they last had sex.

Results: Two men seroconverted during follow-up, both in the event-driven group, for an HIV incidence rate of 0.09 per 100 person-years. The incidence was very low in both groups: 0 and 0.2 per 100 person-years, respectively, among those taking daily and intermittent PrEP. Molina estimated that use of PrEP had averted 143 new HIV infections. Both men who seroconverted had stopped taking PrEP several weeks before and had condomless sex in the interim. One 52-year old man had started on-demand PrEP in April 2016 and enrolled in Prévenir in February 2018. The other, age 47, had started daily PrEP in June 2016 but opted for intermittent dosing when he joined Prévenir in June 2017. Neither showed evidence of resistance to the drugs in Truvada.

The number of sex acts and number of sexual partners was higher in the daily PrEP users compared with the intermittent users. In both groups, the frequency of sex rose by 43% after starting PrEP but then levelled off. Conversely, the number of sexual partners declined by 20% after starting PrEP.
Molina reported that bacterial sexually transmitted infections (STIs) were common, rising by 38% from the start of the study to month 18. The overall incidence rate was 86 per 100 person-years. STIs were more common in the daily PrEP arm, both at the start of the study and at 18 months.

Both daily and event-driven PrEP were well-tolerated. Drug-related adverse events were uncommon and similar in both groups. Only three people stopped taking TDF/FTC due to gastrointestinal side-effects.

Molina also said that nine men on daily PrEP and 11 on intermittent PrEP contracted hepatitis C virus during follow-up. He commented that the viral hepatitis incidence rate of 1.04 per 100 person-years – which included one case each of hepatitis A, B and E – was quite high and researchers were trying to address this issue.

Molina JM et al. Incidence of HIV-infection with daily or on-demand PrEP with TDF/FTC in Paris area. Update from the ANRS Prévenir Study. 10th International AIDS Society Conference on HIV Science, Mexico City, abstract TUAC0202, 2019.

Source: Reporting from Mexico City for PRN News: Bill Valenti. MD

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