Frequency of differential placental transfer to twins of maternal antiretroviral medications.

Background: Placental passage of drugs in twins is poorly understood, and is unknown regarding antiretrovirals (ARVs). In the event of large differences in the exposure of 2 twins to the same maternal therapy, this could have a clinical impact in terms of prevention of perinatal HIV transmission or adverse effects.

Objective: To describe the frequency of differential transplacental passage of antiretrovirals between twins.

Study Design: The study was performed retrospectively, on data from women included in a multicenter perinatal HIV cohort study. All twin pairs for which the mother received antiretroviral therapy and for which drug concentrations in both of the umbilical cords after cord clamping at delivery were studied. We considered that a difference in concentrations of more than 50 % between twins was a substantial difference (ratios below 0.67 or above 1.50).

Results: We analyzed 29 twin pairs, 27 dichorionic and 2 monochorionic diamniotic. Cord blood concentrations differed between the 2 twins by more than 50 % for at least one ARV in 9 twin pairs, 8 dichorionic and 1 monochorionic. Discordant concentrations were observed in one or more cases for several nucleoside reverse transcriptase inhibitors (tenofovir, emtricitabine, lamivudine, zidovudine) and protease inhibitors (atazanavir, lopinavir, saquinavir et ritonavir); within individual twin pairs placental transfer was discordant for one or more ARVs, but identical for others.

Conclusion: Concentrations differed in nearly one third of twin pairs. This may be due to interindividual genetic variability of placental transporters between dizygotic twins as well as physiological differences between twins.