Adolescent decision making about participation in a hypothetical HIV vaccine trial

Purpose The purpose of this study was to examine the process of adolescent decision-making about participation in an HIV vaccine clinical trial, comparing it to adult models of informed consent with attention to developmental differences. Methods As part of a larger study of preventive misconception in adolescent HIV vaccine trials, we interviewed 33 male and female 16–19-year-olds who have sex with men. Participants underwent a simulated HIV vaccine trial consent process, and then completed a semistructured interview about their decision making process when deciding whether or not to enroll in and HIV vaccine trial. An ethnographic content analysis approach was utilized. Results Twelve concepts related to adolescents' decision-making about participation in an HIV vaccine trial were identified and mapped onto Appelbaum and Grisso's four components of decision making capacity including understanding of vaccines and how they work, the purpose of the study, trial procedures, and perceived trial risks and benefits, an appreciation of their own situation, the discussion and weighing of risks and benefits, discussing the need to consult with others about participation, motivations for participation, and their choice to participate. Conclusion The results of this study suggest that most adolescents at high risk for HIV demonstrate the key abilities needed to make meaningful decisions about HIV vaccine clinical trial participation

Vitamin D3 Supplementation Increases Fibroblast Growth Factor-23 in HIV-Infected Youths Treated with Tenofovir Disoproxil Fumarate

BackgroundTenofovir (TDF) is associated with phosphaturia and elevated 1,25 dihydroxy vitamin D (1,25-OH(2)D). Fibroblast growth factor 23 (FGF23) causes phosphaturia and increases in response to elevated 1,25-OH(2)D. Vitamin D-binding protein (VDBP) binds to 1,25-OH(2)D, decreasing its biological activity, and is elevated in individuals with higher plasma tenofovir concentrations. We compared FGF23 and VDBP before and after vitamin D3 (VITD) supplementation in youths treated with combination antiretroviral therapy (cART) containing or not containing TDF.MethodsA randomized controlled trial in HIV-positive youths aged 18-25 years enrolled participants based on cART treatment with TDF (TDF; n=118) or without TDF (no-TDF; n=85), and randomized within those groups to VITD (50,000 IU every 4 weeks) or placebo (PL). We measured FGF23 and VDBP and calculated free 1,25-OH(2)D at baseline and week 12, and compared changes by TDF treatment and VITD randomized group.ResultsAt baseline, serum FGF23 concentration showed a quadratic relationship with 1,25-OH(2)D most pronounced in the TDF group. At week 12, total and free 1,25-OH(2)D increased in the VITD but not PL groups, independent of TDF use. FGF23 increased in the TDF group receiving VITD, but there was no FGF23 change in the no-TDF group receiving VITD or the PL groups. The adjusted mean change in FGF23 from baseline to week 12 was 7.7 pg/ml in the TDF/VITD group, compared with -1.7 (no-TDF/VITD, P=0.010), -1.3 (TDF/PL, P=0.006) and 1.1 (no-TDF/PL, P=0.035).ConclusionsThese results suggest that TDF-containing cART may alter the FGF23 response to vitamin D supplementation in HIV-infected youths. Clinical trials number: NCT00490412

Association of Higher Plasma Vitamin D Binding Protein and Lower Free Calcitriol Levels with Tenofovir Disoproxil Fumarate Use and Plasma and Intracellular Tenofovir Pharmacokinetics: Cause of a Functional Vitamin D Deficiency?

Tenofovir disoproxil fumarate (TDF) causes bone, endocrine, and renal changes by an unknown mechanism(s). Data are limited on tenofovir pharmacokinetics and these effects. Using baseline data from a multicenter study of HIV-infected youth on stable treatment with regimens containing TDF (n = 118) or lacking TDF (n = 85), we measured cross-sectional associations of TDF use with markers of renal function, vitamin D-calcium-parathyroid hormone balance, phosphate metabolism (tubular reabsorption of phosphate and fibroblast growth factor 23 [FGF23]), and bone turnover. Pharmacokinetic-pharmacodynamic associations with plasma tenofovir and intracellular tenofovir diphosphate concentrations were explored among those receiving TDF. The mean age was 20.9 (standard deviation [SD], 2.0) years; 63% were male; and 52% were African American. Compared to the no-TDF group, the TDF group showed lower mean estimated glomerular filtration rates and tubular reabsorption of phosphate, as well as higher parathyroid hormone and 1,25-dihydroxy vitamin D [1,25-OH(2)D] levels. The highest quintile of plasma tenofovir concentrations was associated with higher vitamin D binding protein, lower free 1,25-OH(2)D, higher 25-OH vitamin D, and higher serum calcium. The highest quintile of intracellular tenofovir diphosphate concentration was associated with lower FGF23. Higher plasma tenofovir concentrations were associated with higher vitamin D binding protein and lower free 1,25-OH(2)D, suggesting a functional vitamin D deficiency explaining TDF-associated increased parathyroid hormone. The finding of lower FGF23 accompanying higher intracellular tenofovir diphosphate suggests that different mechanisms mediate TDF-associated changes in phosphate handling. Separate pharmacokinetic properties may be associated with distinct TDF toxicities: tenofovir with parathyroid hormone and altered calcium balance and tenofovir diphosphate with hypophosphatemia and FGF23 regulation. (The clinical trial registration number for this study is NCT00490412 and is available online at http://clinicaltrials.gov/ct2/show/NCT00490412.)

Vitamin D3 Supplementation Increases Spine Bone Mineral Density in Adolescents and Young Adults With Human Immunodeficiency Virus Infection Being Treated With Tenofovir Disoproxil Fumarate: A Randomized, Placebo-Controlled Trial

BackgroundTenofovir disoproxil fumarate (TDF) decreases bone mineral density (BMD). We hypothesized that vitamin D3 (VITD3) would increase BMD in youth receiving TDF.MethodsThis was a randomized, double-blind, placebo-controlled trial of directly observed VITD3 vs placebo every 4 weeks for 48 weeks in youth aged 16-24 years with HIV, RNA load <200 copies/mL, taking TDF-containing combination antiretroviral therapy (TDF-cART) for ≥180 days. Participants (N = 214) received a daily multivitamin containing VITD3 400 IU and calcium 162 mg, plus monthly randomized VITD3 50000 IU (n = 109) or placebo (n = 105). Outcome was change from baseline to week 48 in lumbar spine BMD (LSBMD). Data presented are median (Q1, Q3).ResultsParticipants were aged 22.0 (21.0, 23.0) years, 84% were male, and 74% were black/African American. At baseline, 62% had 25-hydroxy vitamin D (25-OHD) <20 ng/mL. Multivitamin adherence was 49% (29%, 69%), and VITD3/placebo adherence 100% (100%, 100%). Vitamin D intake was 2020 (1914, 2168) and 284 (179, 394) IU/day, and serum 25-OHD concentration was 36.9 (30.5, 42.4) and 20.6 (14.4, 25.8) ng/mL at 48 weeks in VITD3 and placebo groups, respectively (P < .001). From baseline to week 48, LSBMD increased by 1.15% (-0.75% to 2.74%) in the VITD3 group (n = 99; P < .001) and 0.09% (-1.49% to 2.61%) in the placebo group (n = 89; P = .25), without between-group difference (P = .12). VITD3 group changes occurred with baseline 25-OHD <20 ng/mL (1.17% [-.82% to 2.90%]; P = .004) and ≥20 ng/mL (0.93% [-.26% to 2.15%]; P = .033).ConclusionsFor youth taking TDF-cART, LSBMD increased through 48 weeks with VITD3 plus multivitamin, but not with placebo plus multivitamin, independent of baseline vitamin D status.Clinical trials registrationNCT01751646