A 29-year-old woman, G2P1, presents to the labor and delivery unit at 39 weeks of gestation in active labor. She reports spontaneous rupture of membranes approximately 12 hours ago and has had mild intermittent contractions over the past 6 hours. Key History: Positive GBS screening at 36 weeks gestation. Stable maternal vitals, reassuring fetal heart rate. Cervical exam: 4 cm dilation, 80% effacement, -1 station. The obstetric team decides to initiate intrapartum GBS antibiotic prophylaxis due to her positive GBS status and prolonged rupture of membranes. What is the first-line antibiotic for intrapartum GBS prophylaxis?
