Study Design and Participants
CHAPAS-4 (ISRCTN22964075) is an open-label, multicenter, 4 × 2 factorial randomized trial evaluating efficacy and safety of 4 anchor drugs combined with 2 backbone regimens to optimize the second-line treatment of HIV in children aged 3–15 years failing first-line treatment and to better harmonize with adult ART. In this article, we report the pharmacokinetic parameters of TAF and TFV gained from intensive pharmacokinetic substudies nested within the CHAPAS-4 trial. We enrolled children weighing ≥14 kg randomized to FTC/TAF backbone, from 4 sites in Uganda, Zambia, and Zimbabwe. Local ethics committees approved the main trial and pharmacokinetic substudies.Children were enrolled if their parents/caretakers provided written consent to participate in the CHAPAS-4 trial and the pharmacokinetic substudy; verbal consent was reconfirmed before initiating the pharmacokinetic sampling. Older children provided written assent, as per local country guidelines. The consent and assent documents were translated into local languages. Children weighing 14 to <25 kg received 120/15 mg FTC/TAF; those weighing ≥25 kg received 200/25 mg, both as FDC tablets. FTC/TAF was used in combination with 1 of 4 randomized anchor drugs (ie, DTG, ATV/r, DRV/r, or LPV/r) dosed in weight bands (see Daily Dose of Anchor Drugs taken by CHAPAS-4 participants in World Health Organization–Recommended Weight BandsAbbreviations: ATV/r, atazanavir/ritonavir; DRV/r, darunavir/ritonavir; DTG, dolutegravir; LPV/r, lopinavir/ritonavir; QD, once daily; RTV, ritonavir.