• Adverse experiences with a severity of Grade 3 or 4 and adverse pregnancy outcomes that cannot be directly attributed to a cause besides study treatment [ Time Frame: Throughout study ] [ Designated as safety issue: Yes ]
  

• Maternal viral load [ Time Frame: during active labor and 24 to 48 hours, 7 days, 6 to 8 weeks, and 12 weeks postpartum ] [ Designated as safety issue: No ]
  
• viral resistance to emtricitabine/tenofovir disoproxil fumarate using bulk sequencing [ Time Frame: at Weeks 1, 6, and 12 postpartum ] [ Designated as safety issue: No ]
  
• infant HIV DNA PCR [ Time Frame: at 24 to 48 hours, 6 to 8 weeks, 4 months, and 6 months of life ] [ Designated as safety issue: No ]
  

The majority of perinatally infected infants are infected during the labor and delivery process, but recent studies suggest that additional factors, such as postexposure prophylaxis, are likely to be involved in the prevention of MTCT of HIV. It is possible that antiretroviral dosing only during labor and short-term dosing to newly born infants would be sufficiently effective to prevent MTCT of HIV. TDF is a nucleoside reverse transcriptase inhibitor that has demonstrated significant effectiveness in preventing MTCT of simian immunodeficiency virus (SIV) in a primate model of HIV. FTC/TDF is a combination of two NRTIs being studied because this combination has the potential to prevent MTCT, while protecting the mother from developing resistance that may develop with single drug therapy. This study will evaluate the safety, tolerance, and pharmacokinetics (PK) of single doses of TDF and FTC/TDF in both HIV infected pregnant women and their newborn infants.

Cohort 1 is now closed. Each participant in Cohort 1 received a single 600 mg oral dose of TDF at the start of active labor or 4 hours prior to C-section, with concurrent administration of standard intravenous zidovudine (ZDV) prophylaxis and/or other antiretrovirals prescribed by her physician. The infants from Cohort 1 received only the standard 6 weeks of oral ZDV prophylaxis postpartum. PK blood samples were taken from mothers at predose and 1, 2, 4, 8, 12, and 24 hours postdose and at the time of delivery; PK blood samples were taken from infants at 12, 24, and 36 hours after birth.

Pregnant women with HIV infection entering this study will be assigned to Cohort 2, as all infants in Cohort 1 have completed the 6 to 8 week study visit and all Cohort 1 data have been reviewed. Mothers in Cohort 2 will receive a single dose of 900 mg of TDF combined with 600 mg emtricitabine, along with standard ZDV prophylaxis and/or other antiretrovirals prescribed by her physician. Infants will receive a single dose of TDF at 4 mg/kg combined with 3 mg/kg emtricitabine as soon as possible after delivery and within 6 hours of age as well as the standard 6 weeks of oral ZDV prophylaxis after birth. Blood samples from mothers and infants will be taken as for Cohort 1.

Mothers will be followed for 12 weeks postpartum or for 2 years after giving birth if viral resistance to TDF or FTC/TDF is demonstrated at Weeks 1, 6, or 12. In addition to the PK studies, blood collection will occur around the time of delivery, at screening, study entry, at delivery, and after delivery at various times up to Week 12. Physical exams will be done at screening, study entry, at delivery, and after delivery at various times up to Week 8. Infants will be followed until age 2. Blood will be collected and physical exams will be done at birth and at various times up to Week 96. Mothers are encouraged to coenroll in PACTG P1025, Pharmacokinetic Study of Anti-HIV Drugs During Pregnancy.