• Proportion of patients with viral NNRTI mutations detectable during the 4 month follow-up compared with the incidence observed in the PHPT-2 clinical trial, who received the same antiretroviral prophylaxis but no post-partum regimen [ Time Frame: Within 4 months postpartum ] [ Designated as safety issue: No ]
  

Drug: Zidovudine (ZDV)
Zidovudine 300 mg, twice daily, for one month postpartum. Note: after July 03, 2005, all women received 200 mg, twice daily, for the same duration.
Drug: Didanosine (ddI)
250 mg ddI-EC (400 mg if body weight >60 kg) once daily, starting at the onset of labor and for one month postpartum

A single nevirapine dose to the mother, with or without a dose to the child, in addition to oral ZDV prophylaxis starting from 28 weeks gestation has been proven to be highly effective in reducing further mother-to-child HIV transmission (PMTCT).

However, post exposure nevirapine resistance mutations are observed in the mother's viral population. These mutations detectable very early after exposure tend to disappear over time.

Nevertheless, they may be associated with decrease in efficacy of non-nucleoside reverse transcriptase inhibitor (NNRTI) containing regimens subsequently given to the women for their own health.

Therefore, there is a need for research to prevent selection of resistance in the first place or to overcome the resistance in subsequent treatment of the infected mother or infant.

Nevirapine plasma levels above IC50 have been detected in women exposed to a single 200 mg dose of nevirapine in a significant number of women during the third week postpartum.

We hypothesize that giving ZDV+ddI to women exposed to nevirapine for one month as soon as possible after exposure may prevent the selection of nevirapine resistance mutations.