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Women respond best to anti-HIV drugs when the second dose is given at least six months after initial treatment, according to findings in The New England Journal of Medicine.
On the other hand, higher amounts of HIV remain in the blood of women given two treatments within six months.
The anti-HIV drug nevirapine is commonly given to pregnant women during labor to lower the chance that the mother will pass HIV on to her child. Giving a single dose (with or without AZT and lamivudine) is common practice in poor countries where multidrug cocktails are in short supply.
In the study, 218 women in Botswana who had previously received a course of AZT from the 34th week of pregnancy to delivery received a single dose of nevirapine (or placebo) at labor. Recordable levels of HIV were found in 42% of women who had followed the nevirapine with antiretroviral therapy (ART) within six months of delivery. Only 12% of those who received ART more than six months postpartum showed detectable levels.
A single dose of nevirapine destroys most of the HIV but can leave behind a few mutant copies. Researchers have worried that those mutants could make the virus resistant to nevirapine treatment in the future.
The current research shows timing between doses is critical. "The findings show that single dose nevirapine during labor alone--or with short course AZT during pregnancy--remains a viable option in resource-poor settings for preventing the spread of HIV from mother to child among pregnant women who do not yet require anti-HIV treatment for their own health," said Duane Alexander, director of the National Institute of Child Health and Human Development.
The study was funded in part by the National Institutes of Health.