response to antiretroviral therapy after a single peripartum dose of nevirapine background a single dose of nevirapine during labor reduces perinatal transmission of human immunodeficiency virus type 1 hiv1 but often leads to viral nevirapine resistance mutations in mothers and infantsmethods we studied the response to nevirapinebased antiretroviral treatment among women and infants who had previously been randomly assigned to a single peripartum dose of nevirapine or placebo in a trial in botswana involving the prevention of the transmission of hiv1 from mother to child all women were treated with antenatal zidovudine the primary end point for mothers and infants was virologic failure by the 6month visit after initiation of antiretroviral treatment estimated within groups by the kaplanmeier methodresults of 218 women who started antiretroviral treatment 112 had received a single dose of nevirapine and 106 had received placebo by the 6month visit after the initiation of antiretroviral treatment 50 of the women who had received placebo had virologic failure as compared with 184 of those who had received a single dose of nevirapine p0002 among 60 women starting antiretroviral treatment within 6 months after receiving placebo or a single dose of nevirapine no women in the placebo group and 417 in the nevirapine group had virologic failure p0001 in contrast virologic failure rates did not differ significantly between the placebo group and the nevirapine group among 158 women starting antiretroviral treatment 6 months or more post partum 78 and 120 respectively p039 thirty infants also began antiretroviral treatment 15 in the placebo group and 15 in the nevirapine group virologic failure by the 6month visit occurred in significantly more infants who had received a single dose of nevirapine than in infants who had received placebo p0001 maternal and infant findings did not change qualitatively by 12 and 24 months after the initiation of antiretroviral treatmentconclusions women who received a single dose of nevirapine to prevent perinatal transmission of hiv1 had higher rates of virologic failure with subsequent nevirapinebased antiretroviral therapy than did women without previous exposure to nevirapine however this applied only when nevirapinebased antiretroviral therapy was initiated within 6 months after receipt of a single peripartum dose of nevirapine clinicaltrialsgov number nct00197587 clinicaltrialsgov