Organism-specific antibiotic therapy The recommended initial treatment for GBS meningitis in neonates < 1 week of age is penicillin G 100, 000 units / kg IV every 6 hours or ampicillin 100 mg / kg IV every 8 hours for infants ≤ 7 days or 75 mg / kg every 6 hours for infants > 7 days.