Background: Concentration of antiretroviral (ARV) drug found in plasma, and amounts of drug excreted into breastmilk, may affect HIV viral load and potentially perinatal HIV transmission.
Methods: In this cohort study with 2-phase sampling, we included mothers randomized to postpartum maternal ARVs or daily infant nevirapine during 28 weeks of breastfeeding in the Breastfeeding, Antiretrovirals, and Nutrition study. Among these, we included all mothers who transmitted HIV to their infants between 2 and 28 weeks and 15% of mothers who did not (n = 27 and 227, respectively). Spearman correlation coefficients (r) were used to assess the correlation between maternal plasma and breastmilk ARV concentration. Associations between the median effective drug concentration (EC50) and detectable maternal viral load (plasma: >40 copies per milliliter, breastmilk: >56 copies per milliliter) were assessed using mixed-effects models. Cox models were used to estimate the association between maternal or infant plasma drug concentration and breastmilk HIV transmission from 2 to 28 weeks.
Results: All ARV compounds exhibited substantial correlations between maternal plasma and breastmilk concentrations (r: 0.85-0.98, P-value <0.0001). Having plasma drug concentration above the EC50 was associated with lower odds of having detectable HIV RNA [maternal plasma odds ratio (OR) 0.64, 95% confidence interval (CI): 0.45 to 0.91; breastmilk OR 0.22, 95% CI: 0.14 to 0.35] and a reduced rate of breastmilk HIV transmission (hazard ratio 0.40, 95% CI: 0.18 to 0.93). Having breastmilk drug concentration above the EC50 was also associated with lower odds of having detectable maternal HIV RNA (plasma OR 0.62, 95% CI: 0.45 to 0.85; breastmilk OR 0.42, 95% CI: 0.29 to 0.59).
Conclusions: Ensuring adequate drug concentration is important for viral suppression and preventing breastmilk HIV transmission.