IAS: 3TC infant prophylaxis during breast-feeding reduces HIV infection rate at six months

Daily dosing with 3TC (lamivudine, Epivir) for infants of HIV-positive mothers reduces the risk that a baby will acquire HIV infection from its mother through breast-feeding, according to the results of a joint Tanzanian/Swedish study presented last week at the Third International AIDS Society Conference on HIV Treatment and Pathogenesis in Rio de Janeiro, Brazil.

The MITRA study was conducted in Dar es Salaam, Tanzania’s largest city. It recruited pregnant HIV-positive women with a median age of 26 years and median CD4 cell count of 419 cells/mm³. The vast majority of mothers were asymptomatic (WHO stage 1: 89%), but 13.7% had CD4 cell counts below 200 cells/mm³ and thus had a high risk of transmitting HIV to their infants perinatally.

Mothers received treatment according to the PETRA trial protocol, which had tested AZT/3TC (Combivir) given from week 36 of pregnancy until one week after delivery as prophylaxis against mother-to-child transmission. Infants received AZT/3TC for one week after birth, and then received daily treatment with 3TC (4mg/kg) throughout the breast-feeding period. Mothers were counselled to stop breast-feeding by six months after birth, although 22% were still breast-feeding 26 weeks after birth.

HIV infection was significantly less frequent in 3TC-treated infants at six months compared to a historical control group of infants born to mothers who participated in the original PETRA study. Infection was diagnosed using an Amplicor HIV-1 DNA assay, which is the only reliable method of detecting HIV infection in infants.

4.9% of the 3TC-treated infants were HIV-positive by month six, compared to 11.9% of the historical control group (p=0.003). The rate of infection at six months was only slightly higher than the infection rate at week six among the 3TC-treated infants (3.4%).

A potential limitation of this study is that the majority of mothers stopped breast-feeding within six months of delivery, leading some experts to suggest that it is difficult to disentangle the effect of early weaning from the effect of 3TC. However the median duration of breast-feeding was 20 weeks, suggesting an extended period of risk for most infants. The research group did not present any analysis of transmission risk according to maternal baseline characteristics, particularly baseline CD4 cell count, and there was no information on maternal viral load in plasma or breast milk, so it is not possible to determine whether 3TC prophylaxis was more successful for infants of mothers with less advanced HIV disease.