Purpose: Nevirapine is an antiretroviral agent given to HIV-infected women as a single dose for the prevention of mother-to-child transmission (PMTCT) of HIV in resource-poor settings. Although resistance to nevirapine after this single dose decreases the virologic response to later combination antiretroviral therapy (ART) that includes nevirapine, long term outcomes are unknown. Our objective was to evaluate the choice of ART regimen (nevirapine vs. protease inhibitor-based) on the life expectancy of HIV-infected South African women exposed to nevirapine for PMTCT.

   Methods: We developed a Markov model to compare the life expectancies of women previously exposed to nevirapine for PMTCT starting either nevirapine-based, or protease inhibitor-based combination ART. We assumed that women with the following CD4 cell distribution at baseline started ART once the CD4 count fell below 200 cells/ul: 30% >500 cells/ul, 30% 201-500 cells/ul, 30% 51-200 cells/ul, and 10% £50 cells/ul. We modeled decrease in efficacy of nevirapine-based therapy in the presence of drug resistance, and increased efficacy as time from delivery increased. Base case probabilities were from published literature and included 18% nevirapine resistance at 10 days post delivery, efficacy of viral suppression for those with and without nevirapine resistance of 80% and 87% at 3 months, and 68% and 80% at 6 months. We performed a wide range of sensitivity analyses on ART efficacy, prevalence of baseline nevirapine resistance and other parameters.

	Projected life expectancy (months)
ART regimen	Overall	NVP-resistance	No NVP-resistance
NVP-based	94.3	92.7	94.8
PI-based	95.9	95.8	96.3

   Results: For a single ART regimen, PI-based therapy increased overall projected life expectancy by 1.6 months (Table). Women starting nevirapine-based regimens with nevirapine resistance at baseline had lower projected life expectancy than women starting nevirapine therapy without resistance. Results were sensitive to the efficacy of antiretroviral regimens and the initial distribution of CD4 cell counts, but not sensitive to varying the prevalence of baseline nevirapine resistance from 5% to 72%.

   Conclusions: Life expectancy in South African women previously exposed to nevirapine is likely improved with protease inhibitor-based therapy. These results should be considered in developing guidelines for both initial and subsequent therapy for HIV in South Africa.