Timing variations don’t affect nevirapine’s impact on mother-to-child transmission

Variations in the timing of nevirapine (Viramune) dosing for both mother and infant don’t have a significant impact on the effectiveness of nevirapine in preventing mother-to-child transmission, according to an analysis published in the November 4^th edition of the journal AIDS. Mothers who took the drug less than two hours before delivery were no more likely to pass on the virus than women who had taken it more than four hours before delivery, and as long as infants received their dose within 72 hours of delivery, it didn’t seem to matter when they – or their mothers – actually took the drug.

The findings provide important operational information for programmes that are trying to implement nevirapine prophylaxis. Doctors have worried that if women take nevirapine too late, perhaps as a result of late arrival at hospital, the drug might not reach adequate levels in the blood in time to prevent mother-to-child transmission. However, no one had looked at transmission rates in relation to the timing of doses previously.

Researchers involved in the HIVNET 024 study, an international trial that tested the effect of antibiotic treatment of chorioamnionitis on mother to child HIV transmission, analysed whether the timing of maternal and infant nevirapine doses affected the rate of HIV transmission.

All mothers and infants in this study received a single dose of nevirapine. The study protocol specified that mothers should take a dose of nevirapine at the onset of labour, and that the infant should receive a 2mg/kg dose of nevirapine within 72 hours of birth.

The effect of the drug on transmission was assessed by testing infants at birth and again at six weeks using a viral load test. Results were available for 1491 infants out of 2078 live births (153 tested positive at birth, indicating that they had most likely been infected prior to the onset of labour, 92 died before week 6 and the remainder of results were lost to follow-up or missing).

The overall rate of HIV transmission during delivery or in the early postnatal period at week 6 was 8.1%.

Information on nevirapine dose timing was available for 1460 mothers, of whom 15% took their nevirapine less than two hours before delivery, 77% between two and 24 hours, 6% between 24 and 48 hours and 1% over 48 hours prior to delivery.

Dose timing information was available for 1480 infants. Eighteen per cent received their dose less than four hours after delivery, 44% between four and 24 hours after delivery, 36% between 24 and 72 hours and 3% over 72 hours after delivery.

No statistically significant differences in HIV transmission according to dose timing were evident in either group, nor when the risk of transmission was analysed according to times of both infant and maternal dosing.

“Our findings suggest MTCT is not affected by the timing of either maternal or infant dose, so long as they are in reasonable proximity to the time of delivery…within 48 hours of delivery for the maternal [nevirapine] and within 72 hours after birth for the infant dose,” write the authors.

“In settings where health care is sporadic, or where large proportions of women deliver at home, delaying infant nevirapine administration for up to 72 hours does not appear to increase the risk of MTCT provided that the maternal dose was taken in reasonable proximity.”