HIV-positive mothers who have previously used single-dose nevirapine to prevent passing on HIV to their baby during delivery can use the same procedure to prevent transmission in a second delivery, according to the results of a pilot study presented on Thursday at the Twelfth Annual Retrovirus Conference in Boston.
Providing a single dose of the non-nucleoside reverse transcriptase inhibitor (NNRTI) nevirapine to mothers and their newly born babies has been shown to effectively reduce the rate of mother-to-baby transmission of HIV.
Over time, an increasing number of women will take nevirapine in second and subsequent pregnancies to prevent transmission of HIV to their infants. However, resistance to nevirapine can develop when a single dose of the drug is used to prevent mother-to-baby HIV transmission, and it has been theorised that this may reduce the efficacy of the drug when used in second or subsequent pregnancies.
Investigators in Soweto conducted a pilot case-controlled study to compare rates of mother-to-baby HIV transmission in women who used nevirapine in two successive pregnancies, to women giving birth to a second child, but using nevirapine for the first time.
In total 106 women using nevirapine for a second pregnancy were recruited to the study. A further 212 women using nevirapine for the first time were also recruited to the study as controls, and these women were matched on a two-to-one basis with the women using the drug for a second time. The women were recruited from 13 antenatal clinics.
Maternal viral load, CD4 cell count and resistance profile were determined at baseline and six weeks after delivery. HIV infection in the babies was determined by polymerase chain reaction (PCR) testing when they were six weeks old.
Six weeks after delivery, the babies of women using nevirapine in a second pregnancy were more likely to be infected with HIV than those of women using the drug in their first pregnancy (10 vs. 4%), but this was not statistically significant. This, according to presenter Neil Martinson, suggests that the use of nevirapine for a second pregnancy is still of benefit in preventing mother-to-child transmission of HIV, when compared to the drug-free transmission rate of at least 25%.
Prevalence of resistance to nevirapine was also comparable between the two groups of women (38 vs. 50%, p = 0.26). However, the pattern of resistance mutations differed between the groups, with the doubly exposed women tending to have fewer resistance mutations, possibly due to their less advanced HIV disease stage.
The investigators noted that the rate of transmission observed in the infants of mothers using nevirapine for a first pregnancy is very low. On recruitment of more mothers to the study, they predicted that this value may increase to rates similar to those observed in other studies - typically around 10%.
Given the increasing number of women using nevirapine to prevent HIV transmission in second and subsequent pregnancies, the investigators called for further research into the efficacy of this strategy as a matter of urgency.
Martinson N et al. Effectiveness of single-dose nevirapine in a second pregnancy. Twelfth Conference on Retroviruses and Opportunistic Infections, Boston, abstract 103, 2005.