To prevent transmission while breastfeeding, various interventions have been designed that:

• Provide the mother with antiretroviral (ARV) therapy.
• Provide ARV prophylaxis to uninfected infants during the breastfeeding period.
• Use a combination approach, giving ARV therapy to both mother and infant.

Preliminary findings from recent studies show that treatment of HIV-positive breastfeeding mothers with ARV therapy results in reduced viral loads in breastmilk, as well as drug levels in breastmilk that should be sufficient to prevent HIV transmission.

A sub-study of the Mashi trial found that HIV blood levels in the milk of infected women who had been taking a combination of nevirapine, 3TC, and AZT for at least two months were lower than those in women who took only AZT from week 34 of pregnancy with a single dose of nevirapine during labour. All of the milk samples were from the breastfeeding mothers between two and five months after giving birth. However, when investigators measured levels of cell-associated HIV (pro-viral DNA in HIV-infected cells) in the women's breastmilk, there were no significant differences between the two groups of women. It is unknown how much of a transmission risk cell-associated DNA poses to infants. No HIV transmissions were observed in any of the mother-infant pairs during this study. ^[1]

ARV treatment of the mother after delivery may have an added protective benefit to the infant through the delivery of prophylactic ART via breastmilk. In the Mashi trial, Investigators measured the nevirapine, 3TC, and AZT levels in the breastmilk of 20 mothers receiving the three-drug combination and in their infants. In the infants, they found blood levels of nevirapine 40 times the 50% inhibitory concentration (IC₅₀) of 24ng/ml in the infant's blood. (IC₅₀ is the drug concentration that has been shown to inhibit HIV replication by 50%.) This concentration is similar to the level achieved by a single dose of 2mg/kg nevirapine, the dose commonly used for infant prophylaxis. In contrast to nevirapine, 3TC levels were just 5% of the IC₅₀ at a median of 28ng/ml. Median AZT levels were 123ng/ml, 25 times the drug's IC₅₀, but all infants were also receiving oral AZT. Had there been any cases of mother-to-child HIV transmission (MTCT) in this study, any infant not receiving direct ARV therapy (in addition to that received via breastmilk) might have faced the risk of resistance to any or all three drugs.

A report from the DITRAME study showed that AZT monotherapy given for the last two to four weeks of pregnancy and the first week after childbirth reduced HIV levels in breastmilk. Unfortunately, stopping treatment could result in a burst of viral load. This finding suggests that continued ARV therapy for the mother might be well justified until the cessation of breastfeeding.^[2]

The HIVNET 012 study demonstrated that single-dose nevirapine, given at the onset of labour for PMTCT, is more likely to decrease breastmilk viral loads than twice-daily AZT. Six weeks after delivery, there was a four-fold lower transmission rate to infants. However, the 7% transmission rate was higher than that found in the Mashi study.^[3] Use of single-dose nevirapine can also lead to the presence of nevirapine-resistant HIV in the breastmilk that can develop independently of resistance in the blood.^[4] These findings indicate that sustained combination therapy, as in the Mashi study, is required to prevent HIV transmission from mothers who have no alternative to breastfeeding.

The following section presents information from studies that have looked at the strategies of short-term breastfeeding with maternal ART, breastfeeding or formula feeding after short-term ART, extended ART for breastfeeding mothers, and extended infant post-exposure prophylaxis.