Past
studies in monkeys showed that either drug used alone provided partial protection
against rectal infection with a simian virus related to HIV, while daily use of
both agents together provided complete protection.
Further
evidence came from a study by J. Gerardo Garcia-Lerma, presented at the 16th International
HIV Drug Resistance Workshop last month in Barbados, which assessed whether intermittent
PrEP with tenofovir plus emtricitabine around the time of viral exposure would
be as effective as daily administration.
In
this study, macaque monkeys were given subcutaneous injections of 22 mg/kg tenofovir
plus 20 mg/kg emtricitabine either 2 hours before rectal exposure to a hybrid
simian/human immunodeficiency virus (SHIV) (n = 6), or else both 2 hours before
and 24 hours after exposure (n = 6). Control monkeys received no PrEP. All animals
were exposed to SHIV once weekly for up to 14 weeks.
Results
• All 6 monkeys receiving PrEP
both before and after SHIV exposure were protected from infection.
•
Single-dose PrEP administered only prior to exposure provided partial protection,
with 5 of 6 monkeys remaining uninfected.
•
20 of the 21 untreated monkeys were infected with SHIV, mostly during the first
4 exposures.
Conclusion
"Two-dose
PrEP given before and 24 hours after virus exposure can be as effective as daily
PrEP," the researchers concluded. "Single-dose PrEP is highly effective,
but not sufficient to achieve full protection, suggesting that the extended antiviral
activity in the second 24 hour dose also contributes to protection."
In
effect, this study demonstrated the effectiveness of a combination of pre-exposure
and post-exposure prophylaxis (PEP). PEP is currently recommended for healthcare
workers and others with accidental occupational exposure to HIV, as well as for
victims of sexual assault and in cases of condom failure.
PrEP
is currently being studied in injection drug users in Thailand, heterosexual men
and women in Africa, and men who have sex with men in the U.S. and South America.
07/10/07
Reference JG
Garcia-Lerma, R Otten, M Cong, and others. Intermittent Antiretroviral Prophylaxis
with Tenofovir and Emtricitabine (FTC) Protects Macaques Against Repeated Rectal
SHIV Exposures. 16th International HIV Drug Resistance Workshop. St Michael, Barbados.
June 12-16, 2007. Abstract 85.
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