Study design, participants’ sampling and selection
The study was implemented in all four PROMISE-EPI sites. In depth interviews selected in this analysis were conducted with different groups of participants: (1) PROMISE-EPI participants who experienced successively the two types of PNP, (2) Health care providers (HCP) contributing to the PMTCT program in the facilities where the study was implemented, and (3) PROMISE-EPI staff members. A purposive sampling approach was applied to select the participants in each group. Of the 87 PROMISE-EPI participants in Zambia eligible for lamivudine at either EPI-2 or 6 months, 56 could be contacted for this study because they previously consented at the inclusion to the PROMISE-EPI trial. Written informed consent were obtained from HCP and PROMISE-EPI staff members.We conducted both individual interviews and focus group discussions (FGD) with the three types of profiles to take advantage of the strengths of both group and individual data collection methods.Triangulation, through the involvement of the four sites, inclusion of three groups of participants and two types of data collection provided a clear picture of the barriers and facilitators of the two comparable PNP drug regimens and the extended use of lamivudine (