Family planning services, including hormone contraceptives, are critical for HIV-infected women, in whom prevention of unintended pregnancy not only decreases maternal and child mortality, but also reduces the risk of mother-to-child HIV transmission. Similarly, antiretroviral therapy (ART) is a lifesaving intervention that improves the health and economic status of HIV-infected women throughout the world. Therefore, it is of significant public health importance to guide the appropriate use these essential medications. To this end, millions of HIV-infected women in low and middle income countries (LMIC) currently use or are gaining access to subdermal progestin-containing implants as a preferred method of long-acting reversible contraception. These implants are often combined with ART despite the lack of critically needed pharmacokinetic (PK) drug-interaction data to inform their safe and effective concomitant use. Highlighting this concern are several case reports of unintended pregnancy that occurred in patients with subdermal progestin-containing implants concurrently receiving non-nucleoside reverse transcriptase inhibitor (NNRTI)-based ART, the most commonly used ART in LMICs. While NNRTIs are known to significantly decrease oral pill progestin concentrations, no data are available to inform healthcare providers of the impact of NNRTIs on progestin concentrations following release from subdermal implants. To fill this critical gap in knowledge, the overall aim of this proposal is to conduct a PK study to evaluate the combination of a levonorgestrel (LNG) implant and NNRTI (nevirapine or efavirenz)-based ART in HIV-infected Ugandan women. The investigators propose that lower LNG concentrations will be observed in patients on NNRTI-based ART and although the implant's efficacy may be retained initially, this negative interaction will jeopardize implant effectiveness near the end of its intended duration of use (5 years). The specific aims of this project are (1) to characterize the PK of LNG released from a subdermal implant over one year in HIV-infected women with and without NNRTI-based ART and (2) to evaluate the potential for a bidirectional drug-interaction resulting from the long-term impact of chronic progestin exposure on antiretroviral concentrations. To achieve these aims, this study will enroll 20 HIV-infected women into each of three study groups: a control group not receiving ART and two treatment arms consisting of patients receiving nevirapine- or efavirenz- based ART. Using sparse PK sampling strategies, LNG, nevirapine or efavirenz concentrations will be measured over one-year and compared between and within groups, as appropriate. The LNG data will also be used to develop a PK model that will predict LNG disposition over the following three years of intended use, allowing for identification of the safe duration of LNG implant use in women on NNRTI-based ART. At the conclusion of this project, the first evidence-based medical knowledge will be available to guide the safe and effective concomitant use of subdermal LNG implants and NNRTIs, thereby improving management of reproductive health in millions of HIV-infected women worldwide.