Scarsi KK, et al. - Researchers examined alteration in plasma concentrations of vaginally administered etonogestrel and ethinylestradiol following the administration of antiretroviral therapy (ART) containing either efavirenz or ritonavir-boosted atazanavir and evaluated changes in ART concentrations during the use of an intravaginal ring. At HIV clinics in Asia (two sites), South America (five), sub-Saharan Africa (three), and the USA (11), a parallel, three-group, pharmacokinetic evaluation was conducted between Dec 30, 2014, and Sept 12, 2016. Women with HIV who were either ART-naive (control group; n = 25), receiving efavirenz-based ART (n = 25), or receiving atazanavir–ritonavir-based ART (n = 24) were included. On day 21 of intravaginal ring use, participants receiving efavirenz vs the control group had 79% lower etonogestrel and 59% lower ethinylestradiol concentrations. By contrast, participants receiving ritonavir-boosted atazanavir vs the control group had 71% higher etonogestrel, yet 38% lower ethinylestradiol. Findings thereby indicated significantly lower hormone exposure when an intravaginal ring contraceptive was combined with efavirenz-based ART.