Taking HIV pre-exposure prophylaxis (PrEP)
does not lead to increased levels of sexual risk behaviour among gay men,
investigators from the United States report in the online edition of the Journal of Acquired Immune Deficiency
Syndromes. Numbers of sexual partners fell, as did the proportion of men
reporting unprotected anal sex.
“We found no evidence of risk compensation
among at-risk MSM [men who have sex with men] initiating PrEP,” comment the
authors. “Mean numbers of partners and the proportion of men reporting UAS
[unprotected anal sex] decreased significantly from baseline during 24 months
PrEP is an emerging HIV prevention
technology. It involves HIV-negative individuals taking daily antiretroviral
therapy to reduce their risk of infection with the virus. In 2010, results of
the iPrEx trial involving gay and other MSM showed that daily PrEP with Truvada (FTC and tenofovir) reduced the
risk of infection with HIV by 44% overall, with high efficacy seen in people
with the best treatment adherence. Although the results of PrEP studies
involving heterosexuals have been mixed, the United States Food and Drug
Administration approved Truvada for
use as PrEP by adults with a high risk of HIV infection.
However, there is concern in some quarters
that use of PrEP may lead to increases in sexual risk behaviour. Mathematical
models suggest that even modest increases in the proportion of gay men
reporting unprotected sex could wipe out the beneficial effect of PrEP at a
community level. However, the precise impact of PrEP on sexual risk taking is
Data gathered during a PrEP safety study
allowed investigators to explore the impact of PrEP on the sexual risk
behaviour of HIV-negative gay men with a high risk of infection with HIV.
A total of 400 men were recruited to the
study between 2005 and 2007. All reported anal sex with another man in the
preceding twelve months. The study was double blind and placebo controlled.
Participants were randomised either to start treatment immediately or to wait
for nine months. The men were interviewed at baseline and then every three
months about their sexual risk behaviour and use of recreational and erectile
dysfunction drugs. The study lasted 24 months.
At baseline, the men reported a mean of
7.25 sexual partners in the previous three months. This fell significantly
during follow-up to a mean of 6 partners between months 3 and 9 and a mean of 5.71
partners between months 12 and 24 (p < 0.001). These declines were similar in
the immediate- and delayed-treatment arms.
The mean number of reported HIV-positive
partners or partners of an unknown status fell from 4.17 at baseline to 3.51
partners between months 3 and 9 and 3.37 partners between months 12 and 24 (p = 0.01).
There was also a significant fall in the number of reported partners believed
to be HIV negative.
Use of poppers (p < 0.001), erectile
dysfunction drugs (p < 0.001) and a
higher perception of the efficacy of PrEP (p = 0.04) were all associated with
reporting higher numbers of sexual partners during follow-up.
At the start of the study, 57% of men
reported unprotected anal sex in the previous three months. The proportion fell
to 48% between months 3 and 9 (p = 0.001)
and to 52% between months 12 and 24 (p = 0.03).
The proportion of men reporting unprotected
sex between months 3 and 9 was similar between the immediate- and delayed-treatment
There was also a fall in the proportion of
men reporting unprotected sex with an HIV-positive partner, from 29% at
baseline to 21% between months 3 and 9 and 22% between months 12 and 24 (p < 0.001). Declines in unprotected sex with
HIV-positive partners were seen in both the immediate- and delayed-treatment arms.
Factors associated with reporting
unprotected sex during follow-up included younger age (p = 0.01), use of
poppers (p = 0.02), erectile dysfunction treatments (p < 0.001) and
methamphetamine (p < 0.001).
Participation in the study did not lead to
an increase in the number of reported episodes of unprotected anal sex, which
remained steady between months 3 and 9 and months 12 and 24 in both the immediate- and delayed-treatment arms.
There was a fall in reported episodes of
unprotected sex with HIV-positive partners from two in the previous three-month
period at baseline to 1.37 between months 12 and 24 (p = 0.05). This was the case
for both the immediate- and delayed-treatment study arms.
In contrast, the number of episodes of
unprotected anal sex with partners thought to be HIV negative increased between
baseline and months 12 and 24 (2.75 Vs. 4; p = 0.01).
“These changes may represent a possible
increase in seroadaptive practices, in which men preferentially have more
episodes of UAS with assumed HIV-negative partners,” comment the authors.
They also note “men in this study received
risk-reduction counseling, condoms and lubricants, regular HIV/STI testing, and
linkage to prevention services…which may explain the observed risk reduction
and could explain the observed risk declines and could mitigate any potential
for risk compensation.”
Despite this, the investigators were
encouraged by their results, which they believe “provide important information
on changes in risk practices among MSM in the US initiating PrEP in a clinical