A study from Amsterdam found that gay men who had used post-exposure prophylaxis (PEP) in the past were four times more likely than non-users to subsequently become infected with HIV.
PEP failure does not appear to be the cause of their HIV infection, but rather ongoing risk behaviour following a course of PEP. Self-reported adherence to the PEP regimen was high, at 94%.
The investigators compared HIV infection rates between 2000 and 2009 in 355 men, who had in total received 385 courses of PEP, with infection rates over the same period in 782 gay men entering the Amsterdam Cohort Study. They measured HIV incidence three and six months after receiving PEP in the former group and after cohort entry in the latter.
HIV incidence, translated into infections per man per year, was 6.4% in men who had taken PEP and 1.6% in the cohort study. Three out of the eleven PEP users who acquired HIV were positive three months after PEP but the other eight were only found to be positive six months later, indicating that few - if any - infections were acquired while actually taking PEP.
“Our study showed a high incidence of HIV among MSM [men who have sex with men] who used PEP, an indication of ongoing risk behaviour,” write the investigators. “This implies that PEP alone for this group is not sufficient to prevent HIV infection, and a combination of other more comprehensive preventative strategies is needed.”
Comment: It is important not to interpret this study as a failure of PEP. Instead, it indicates that gay men who come forward for PEP rightly see themselves as being at high risk of HIV, but find that PEP is not a strategy they can use often enough for it to be protective. Previous studies of PEP have also found that, while it has an efficacy of about 80% for individual infections, its use makes no difference to infection rates on a population level. The high HIV incidence in PEP seekers suggests that they might be ideal candidates to be offered an ongoing course of PrEP (pre-exposure prophylaxis). At present, PrEP is still regarded as an experimental prevention technique and access to it is limited to unlicensed or clinical trial-based use.





