Evaluations of HIV-1 resistance patterns in trials of pMTCT have demonstrated nevirapine resistant HIV-1 isolates in approximately 15-20% of mothers 4-6 weeks after receiving either a single or two dose 200mg nevirapine regimen. Although the ability to detect these genotypic mutations decreases to 0% by about 18 months, it is not clear whether this resistance is clinically significant.(HIVNET 012).