New IPERGAY analysis shows on-demand PrEP dosing works with less frequent sex

A new subgroup analysis from the French/Canadian ANRS IPERGAY study provided new results from people using IPERGAY dosing for infrequent sex.

Dosing in IPERGAY involved taking four pills for someone having sex once: a double-dose 24 to 2 hours before sex and two single doses 24 and 48 hours after the first dose.

This infrequent sex subgroup is important as majority of participants in IPERGAY were having sex every week (median 10 times a month), generating a dataset for the overall study from taking four doses of PrEP a week (median 15 pills a month).

Frequent IPERGAY dosing has different pharmacokinetics to single use of four doses, given both drugs in PrEP have long half-lives, especially tenofovir in rectal tissue.

Guillemette Antoni presented results from a new analysis of participants who were only using on-demand dosing for less frequent sex, defined as routinely using PrEP for sex over a three month period, but taking <15 pills a month. This was taken as a good marker for true on-demand dosing. Individual participants varied in PrEP use during the study and only contributed appropriate follow up time for this analysis. Combined analysis of antigen/antibody, RNA and Fiebig stage results were used to accurately attribute likely dates of infection within the three-month window for reported PrEP use.

There was approximately 134 patient years of follow up (PYFU) from 269 participants, equally divided between the active vs placebo arms. This subgroup reported having sex a median of 5 (IQR: 2 to 10) times a month, using a median of 9.5 (IQR: 6 to 13) pills a month.

All six infections occurred in the placebo arm. This produced incidence rates of 9.3 /100 PY (95%CI: 3.4 to 20.1) vs 0.0 (0.0 to 5.4) and a significant relative reduction rate of 100% (95%CI: 39 to 100), p=0.13. Similar results were found when the analysis was restricted to periods when participants reported not using condoms.

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These results are important. Even though the study numbers are low in terms of follow up time, the randomised design and significant differences between arms show this that IPERGAY dosing is significantly effective compared to no PrEP.

The degree of protection would need longer follow-up, even though this is unlikely to be available.

Antoni G et al. On-demand PrEP with TDF/FTC remains highly effective among MSM with infrequent sexual intercourse: a sub-study of the ANRS IPERGAY trial. IAS 2017, 23–26 July 2017, Paris. Oral abstract TUAC0102.
programme.ias2017.org/Abstract/Abstract/3629 (abstract)
www.youtube.com/watch?v=vvKApONuutE (webcast, second presentation)