Choices for antibiotics include the following: For women without penicillin allergy: Penicillin G 5 million units IV followed by 2.5 million units every 4 hours or ampicillin 2 g IV followed by 1 g every 4 hours For women with penicillin allergy but a low risk of anaphylaxis (eg, maculopapular rash with prior use): Cefazolin 2 g IV followed by 1 g every 8 hours For women with penicillin allergy and an increased risk of anaphylaxis (eg, bronchospasm, angioneurotic edema, or hypotension with prior use, particularly within 30 minutes of exposure): Clindamycin 900 mg IV every 8 hours if anovaginal cultures show susceptibility; if cultures document resistance or results are unavailable, vancomycin 20 mg / kg IV every 8 hours (maximum dose of 2 g) Tocolytics If the cervix dilates, tocolytics (drugs that stop uterine contractions) can usually delay labor for at least 48 hours so that corticosteroids can be given to reduce risks to the fetus.