Three-drug combination of antiretroviral regimens has been used increasingly in HIV-infected pregnant women worldwide, both for the prevention of mother to child transmission of HIV (PMTCT) and for women's own health. Use of these drugs in pregnant women solely for PMTCT means that these drugs will need to be discontinued in the majority of women after delivery.

Certain antiretroviral regimens contain drugs with long half-life (drugs that stay in the body for a longer period of time after discontinuation than other drugs in the same regimen), such as nevirapine (NVP). HIV can easily develop resistance to NVP when NVP is the only drug left in the body (similar to monotherapy). Given two other drugs for up to 1 week after discontinue NVP (to mimic three-drug regimen while waiting for NVP elimination) can help reduce, but not eliminate, the development of resistant virus.

Unfortunately, NVP-containing regimens are the most widely used regimens for pregnant women in developing countries due to its low cost and its availability in fixed-dose combinations. These study will explore how fast NVP is eliminated from women after delivery and to see if given zidovudine/lamivudine (AZT/3TC) for 1 or 2 weeks after NVP discontinuation can help reduce the development of NVP resistant virus.

Inclusion Criteria:

1. Willing and able to provide 2 separated written informed consents to take part in the Thai Red Cross PMTCT program and in the study
2. Female and aged between 18-45 years
3. Documented HIV-1 infection
4. Pregnant for a maximum of 36 weeks at the first dose of study medication
5. Baseline CD4 cell count >250 cells/mm3
6. Intend to discontinue ART after delivery

Exclusion Criteria:

1. History of significant reaction or allergy to the drugs that may be used in the study
2. Antiretroviral (ARV)-experienced including previous ARV use for the prevention of mother-to-child transmission of HIV
3. Documented NVP- or 3TC-resistant HIV-1 strains
4. Concomitant use of medications that interfere with NVP plasma level
5. Serum aspartate transaminase (AST) or alanine transaminase (ALT) >1.25 times the upper limit of normal
6. Inability to understand the nature and extent of the trial procedures required
7. Pregnant woman, in the opinion of the investigator, should not participate in the study