The study design is a prospective phase I pharmacokinetic study focused on dosing of 500 mg oral amoxicillin administration in pregnant women in the 2nd and 3rd trimester.

Twenty adult pregnant women in good health who are admitted for preterm premature rupture of membranes (24-34 weeks gestational age) will be enrolled in this intensive pharmacokinetic study. Basic information will be collected from the medical record including age, weight, height, pregnancy dating, medications, and allergies.

Inclusion Criteria:

1. Pregnant, engaged in prenatal care with a medical provider (at least one visit)
2. Estimated gestational age 24-34 weeks
3. Able to provide informed consent
4. English speaking

Exclusion Criteria:

1. Receipt of amoxicillin within the past 7 days. (Routine GBS prophylaxis with ampicillin or other antibiotic and routine surgical prophylaxis prior to cesarean with cephalexin and azithromycin 500 mg IV is allowed).
2. Known hypersensitivity or intolerance of amoxicillin, penicillin, other beta lactam or cephalosporin antibiotics.
3. Known renal impairment (serum creatinine ≥1.2 mg/dL).
4. Active concomitant medications known to interact with amoxicillin: allopurinol, methotrexate, mycophenolate, immune checkpoint inhibitors (ie. pembrolizumab), tetracyclines (ie. doxycycline), vitamin K antagonists (ie. warfarin), aminoglycosides (ie. gentamicin).