Infant exposure to antiretroviral drugs and HIV RNA in breastmilk of women living with HIV

Background Treatment of women living with HIV with antiretroviral drugs significantly reduces the risk of HIV transmission via breastmilk. However, infant toxicity due to drug exposure through breastfeeding and breastmilk HIV RNA dynamics under sustained maternal viral suppression remains insufficiently characterized. Methods In a pragmatic study complemented by biobank data, paired maternal and infant plasma as well as breastmilk samples were collected during monthly follow-up. Drug concentrations were measured and used to calculate breastmilk to maternal blood plasma ratios, daily infant dose, and relative infant dose. HIV RNA was also measured in both infant and maternal plasma and breastmilk. Results 21 mother-infant pairs were included, and plasma and breastmilk concentrations were determined for nine different drugs. The breastmilk to plasma ratio varied per drug, but the relative infant dose was below the safety threshold of 10% for all drugs used in this cohort. The highest relative infant dose was 6.94 % for efavirenz. Infant plasma concentrations were either very low or too low to quantify (34.8% below the limit of quantification). HIV RNA was not detected in maternal plasma, in breastmilk, or in infant plasma during breastfeeding and after breastfeeding cessation. Conclusion Infant exposure to antiretroviral drugs is minimal, suggesting negligible toxicity risk. The absence of detectable HIV RNA in breastmilk samples supports current breastfeeding practices in comparable healthcare settings with sufficient monitoring opportunities.