Pharmacokinetics and Safety of Bictegravir in Pregnant and Postpartum Persons With HIV and Their Infants

Background: Limited data exist on bictegravir pharmacokinetics in pregnancy among persons with HIV (PWH) and infant washout. Setting: Nonrandomized, open-label, multicenter phase-IV prospective study of bictegravir pharmacokinetics and safety in pregnant PWH and their infants. Methods: Steady-state 24-hour pharmacokinetic sampling of oral bictegravir 50 mg once daily (a component of fixed-dose combination bictegravir/emtricitabine/tenofovir alafenamide) during the second and third trimesters and postpartum was performed. Cord blood and infant washout samples were collected. Total and free bictegravir concentrations were measured by validated liquid chromatography with tandem mass spectrometry methods. Within-participant geometric mean ratios (GMR) with 90% confidence intervals (CI) were calculated to compare pharmacokinetics between second and third trimester versus postpartum. Infant HIV testing results were obtained. Results: Twenty-seven maternal–infant pairs were enrolled. Bictegravir area under the concentration–time curve from time 0 through 24 hours post-dose was 46% lower in the second trimester (n = 12; P = 0.002; GMR 0.54; 90% CI: 0.43 to 0.69) and 52% lower in the third trimester (n = 24; P, 0.0001; GMR 0.48; 90% CI: 0.43 to 0.55), compared with postpartum. C₂₄ concentrations were above the estimated bictegravir protein-adjusted 95% effective concentration of 0.162 mg/mL. The median ratio of cord-to-maternal blood concentration was 1.38 (n = 17; quartiles: 1.17–1.63). Median T_1/2 for infant bictegravir washout was 33.2 hours (quartiles: 25.7–45.9) with a C_max of 2.06 mg/mL (quartiles: 1.37–2.72). Overall, 88%–92% of participants maintained suppression, 40 copies/mL throughout pregnancy and postpartum. All available infant HIV testing results were negative. The safety profile for pregnant PWH and infants was acceptable. Conclusions: Bictegravir exposure was lower during pregnancy compared with postpartum, yet C₂₄ concentrations were greater than the bictegravir protein-adjusted 95% effective concentration.