Antiretroviral prevention: oral PrEP, gels and treatment studies

Simon Collins, HIV i-Base

One of the most important themes from the conference this year was the high profile given to research into medical interventions to reduce transmission.

Last year, when the iPrEx and Caprisa 004 studies showed proof of principal for oral and topical use of ARVs to reduce the risk of sexual transmission, the differences between actual and reported adherence complicated the interpretation of the potential benefits.

These and other aspects of this research were addressed in many of the studies presented at CROI. This included two separate oral sessions and a plenary talk all of which are available as webcasts. [1, 2, 3]

Despite the high potential benefit for oral PrEP to reduce infections, the idea of using an oral antiretroviral to prevent transmission seems to make some people angry, to the point of losing the science and becoming blind to the level of protection already seen.

The increasing incidence of sexual transmissions in every country directly challenges the efficacy of condoms, however effectively they can protect sexual health including from HIV.

The safety concerns include daily tenofovir having a small impact on bone mineral density, the clinical importance of which is currently unclear. This is less than the impact reported in HIV-positive people on treatment and may be mitigated by intermittent dosing. Although intermittent dosing (once or twice weekly) would reduce cost and improve adherence this will depend on drug levels in tissue rather than blood. The use of intermittent dosing is supported by sustained drug levels in blood achieved with this strategy. However, protection comes from drug levels in the vaginal, rectal or penile tissue where HIV exposure takes place.

The risk of drug resistance from continuing to use tenofovir/FTC by people who become infected was not seen in iPrEx, but resistance data from daily dosing is very preliminary and based on frequent monitoring.

No one in this field is suggesting that oral PrEP becomes the only prevention technology, or even that it is ready for widespread use. The data do support use in specific circumstances, in high-risk individuals who include it to increase their protection.

CROI included studies looking at these issues and our reports in this issue include:

  • Further efficacy analyses from the iPrEx study
  • Bone mineral density (BMD) changes in HIV-negative men using tenofovir
  • Topical gels as PEP and PrEP in human and animal studies


Unless mentioned otherwise, all references are to the Programme and Abstracts of the 18th Conference on Retroviruses and Opportunistic Infections, 28 February–2 March 2011, Boston.

Webcasts are available at the following link:

  1. Oral abstract session: HIV Prevention: HSV2, Topical and Oral PrEP, and Circumcision, Monday 28 February 10:00 AM.
  2. Oral abstract session: Advances in PrEP, Tuesday 1 March, 10.00 AM.
  3. Celum C. Plenary 3/2/2011 8:30 AM Drugs for Prevention–Topical and Systemic PrEP. Wednesday 2 March 8:30 AM.

Links to other websites are current at date of posting but not maintained.