fraction of gauche conformers of N,N-dimethylsuccinamic acid (1) and
its Li+, Na+, K+, Mg2+, Ca2+, and N(Bu)4+ salts were estimated
in DMSO and D2O solution by comparing the experimental
vicinal proton–proton couplings determined by 1H
NMR spectroscopy with those calculated using the Haasnoot, de Leeuw,
and Altona (HLA) equation. In DMSO, the gauche preferences
were found to increase with decreasing Ahrens ionic radius of the
metal counterion. The same trend was not seen in D2O, where
the gauche fraction for all of the metallic salts
were estimated to be approximately statistical or less. This highlights
the importance of metal chelation on the conformation of organic molecules
in polar aprotic media, which has implications for protein folding.
Young men who have sex with men (MSM) and MSM of color have the highest HIV incidence in the US. To explore possible explanations for these disparities and known individual risk factors we analyzed the per-contact risk (PCR) of HIV seroconversion in the early highly active antiretroviral therapy era.
Data from three longitudinal studies of MSM, HIVNET Vaccine Preparedness Study, EXPLORE behavioral efficacy trial, and VAX004 vaccine efficacy trial were pooled. The analysis included visits where participants reported unprotected receptive anal intercourse (URA), protected receptive anal intercourse (PRA), or unprotective insertive anal intercourse (UIA) with an HIV seropositive, unknown HIV serostatus, or an HIV seronegative partner. We used regression standardization to estimate average PCRs for each type of contact, with bootstrap confidence intervals.
The estimated PCR was highest for URA with an HIV seropositive partner (0.73%; 95%BCI 0.45%-0.98%) followed by URA with a partner of unknown HIV serostatus (0.49%; 95%BCI 0.32%-0.62%). The estimated PCR for PRA and UIA with an HIV seropositive partner was 0.08% (95%BCI 0.0%-0.19%) and 0.22% (95%BCI 0.05%-0.39%) respectively. Average PCRs for URA and UIA with HIV seropositive partners were higher by 0.14-0.34% among younger participants and higher by 0.08% for UIA among Latino participants compared to White participants. Estimated PCRs increased with increasing number of sexual partners, use of methamphetamines or poppers, and history of sexually transmitted infection.
Susceptibility or partner factors may explain the higher HIV conversion risk for younger MSM, some MSM of color, and those reporting individual risk factors.
HIV; MSM; USA; per contact risk
In 2010, the iPrEx study demonstrated efficacy of daily emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) pre-exposure prophylaxis (PrEP) in reducing HIV acquisition among men who have sex with men. Adherence to study product was critical for PrEP efficacy, and varied considerably, with FTC/TDF detection rates highest in the United States. We conducted a qualitative study to gain insights into the experiences of iPrEx participants in San Francisco (SF) where there was high confirmed adherence, to understand individual and contextual factors influencing study product use in this community. In 2009 and 2011, we conducted focus groups and in-depth interviews in 36 and 16 SF iPrEx participants, respectively. Qualitative analyses indicate that participants joined the study out of altruism. They had a clear understanding of study product use, and pill taking was facilitated by establishing or building on an existing routine. Participants valued healthcare provided by the study and relationships with staff, whom they perceived as nonjudgmental, and found client-centered counseling to be an important part of the PrEP package. This facilitated pill taking and accurate reporting of missed doses. Adherence barriers included changes in routine, side effects/intercurrent illnesses, and stress. Future PrEP adherence interventions should leverage existing routines and establish client-centered relationships/ environments to support pill taking and promote accurate reporting.
To evaluate for changes in sexual behaviors associated with daily pill-use among MSM participating in a PrEP trial.
Randomized, double-blind, placebo-controlled trial. Participants were randomized 1:1:1:1 to receive tenofovir disoproxil fumarate or placebo at enrollment or after a 9-month delay and followed for 24 months.
400 HIV-negative MSM reporting anal sex with a man in the past 12 months and meeting other eligibility criteria enrolled in San Francisco, Atlanta, and Boston. Sexual risk was assessed at baseline and quarterly visits using Audio Computer-Assisted Self-Interview. The association of pill-taking with sexual behavior was evaluated using logistic and negative-binomial regression for repeated measures.
Overall indices of behavioral risk declined or remained stable during follow-up. Mean numbers of partners and proportion reporting unprotected anal sex (UAS) declined during follow-up (p<0.05), and mean UAS episodes remained stable. During the initial 9 months, changes in risk practices were similar in the group that began pills immediately vs. those in the delayed arm. These indices of risk did not differ significantly after initiation of pill-use in the delayed arm or continuation of study medication in the immediate arm. Use of poppers, amphetamines, and sexual performance-enhancing drugs were independently associated with one or more indices of sexual risk.
There was no evidence of risk compensation among HIV-uninfected MSM in this clinical trial. Monitoring for risk compensation should continue now that PrEP has been shown to be efficacious in MSM and other populations and will be provided in open-label trials and other contexts.
risk compensation; behavioral disinhibition; sexual risk behavior; PrEP; MSM
Combination HIV prevention is a high priority for increasing the impact of partially efficacious HIV prevention interventions for specific populations and settings. Developing the package requires critical review of local epidemiology of HIV infection regarding populations most impacted and most at risk, drivers of HIV infection, and available interventions to address these risk factors. Interventions should be considered in terms of the evidence basis for efficacy, potential synergies, feasibility of delivery at scale, which is important in order to achieve high coverage and impact, coupled with high acceptability to populations, which will impact uptake, adherence, and retention. Evaluation requires process measures of uptake, adherence, retention, and outcome measures of reduction in HIV infectiousness and acquisition. Three examples of combination prevention concepts are summarized for men who have sex with men (MSM) in the Americas, young women in sub-Saharan Africa, and HIV-1 serodiscordant couples.
Combination HIV prevention; integrated prevention; men who have sex with men; young women in Africa; HIV-1 serodiscordant couples
Pre-exposure prophylaxis (PrEP), in which HIV-uninfected persons with ongoing HIV risk use antiretroviral medications to reduce their risk of acquiring HIV infection, is an efficacious and promising new HIV prevention strategy. The past two years have seen significant new advances in knowledge regarding PrEP, including definitive demonstration that PrEP reduces the risk of HIV acquisition, regulatory approval of combination oral emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) as the first PrEP agent with a label indication for sexual HIV prevention, and the development of normative guidance for clinical prescribing of PrEP. In PrEP clinical trials, HIV protection was strongly correlated with PrEP adherence; therefore understanding and supporting adherence to PrEP are key to maximizing its public health impact. As would be expected for any new HIV prevention approach, questions remain, including how to motivate uptake of and sustain adherence to PrEP for HIV prevention in high-risk populations, how much use is sufficient to achieve HIV protection, and the potential of “next-generation” PrEP agents to improve this effective prevention strategy. At this important transition point – from demonstration of efficacy in clinical trials to thinking about implementation and effectiveness – this review addresses where we have been and where we are going with PrEP for HIV prevention.
HIV prevention; pre-exposure prophylaxis; sexual HIV transmission
Syphilis infection was associated with HIV incidence in an HIV-prevention trial that randomized participants to once-daily emtricitabine/tenofovir (FTC/TDF) vs placebo. FTC/TDF had no effect on the association between incident syphilis and HIV acquisition; syphilis infection did not decrease FTC/TDF efficacy.
Background. Syphilis infection may potentiate transmission of human immunodeficiency virus (HIV). We sought to determine the extent to which HIV acquisition was associated with syphilis infection within an HIV preexposure prophylaxis (PrEP) trial and whether emtricitabine/tenofovir (FTC/TDF) modified that association.
Methods. The Preexposure Prophylaxis Initiative (iPrEx) study randomly assigned 2499 HIV-seronegative men and transgender women who have sex with men (MSM) to receive oral daily FTC/TDF or placebo. Syphilis prevalence at screening and incidence during follow-up were measured. Hazard ratios for the effect of incident syphilis on HIV acquisition were calculated. The effect of FTC/TDF on incident syphilis and HIV acquisition was assessed.
Results. Of 2499 individuals, 360 (14.4%) had a positive rapid plasma reagin test at screening; 333 (92.5%) had a positive confirmatory test, which did not differ between the arms (FTC/TDF vs placebo, P = .81). The overall syphilis incidence during the trial was 7.3 cases per 100 person-years. There was no difference in syphilis incidence between the study arms (7.8 cases per 100 person-years for FTC/TDF vs 6.8 cases per 100 person-years for placebo, P = .304). HIV incidence varied by incident syphilis (2.8 cases per 100 person-years for no syphilis vs 8.0 cases per 100 person-years for incident syphilis), reflecting a hazard ratio of 2.6 (95% confidence interval, 1.6–4.4; P < .001). There was no evidence for interaction between randomization to the FTC/TDF arm and incident syphilis on HIV incidence.
Conclusions. In HIV-seronegative MSM, syphilis infection was associated with HIV acquisition in this PrEP trial; a syphilis diagnosis should prompt providers to offer PrEP unless otherwise contraindicated.
chemoprophylaxis; HIV prevention; MSM; preexposure prophylaxis; syphilis
In addition to protecting against HIV acquisition, antiretroviral preexposure prophylaxis (PrEP) using topical 1% tenofovir gel reduced Herpes simplex virus type 2 (HSV-2) acquisition by 51% among women in the CAPRISA 004 study. We examined the effect of daily oral emtricitabine/tenofovir (FTC/TDF) PrEP on HSV-2 seroincidence and ulcer occurrence among men who have sex with men (MSM) in the iPrEx trial.
HSV-2 serum testing was performed at screening and every six months. Among HSV-2-seronegative individuals, we used Cox regression models to estimate hazard ratios (HRs) of HSV-2 seroincidence associated with randomization to FTC/TDF. We used multiple imputation and Cox regression to estimate HRs for HSV-2 seroincidence accounting for drug exposure. We assessed ulcer occurrence among participants with prevalent or incident HSV-2 infection.
Of the 2,499 participants, 1383 (55.3%) tested HSV-2-seronegative at baseline, 892 (35.7%) tested positive, 223 (8.9%) had indeterminate tests, and one test was not done. Of the 1,347 HSV-2-seronegative participants with follow-up, 125 (9.3%) had incident HSV-2 infection (5.9 per 100 person-years). Compared with participants receiving placebo, there was no difference in HSV-2 seroincidence among participants receiving FTC/TDF (HR 1.1, 95% CI: 0.8–1.5; P = 0.64) or among participants receiving FTC/TDF with a concentration of tenofovir diphosphate >16 per million viable cells (HR 1.0, 95% CI: 0.3–3.5; P = 0.95). Among participants with HSV-2 infection, the proportion with ≥1 moderate or severe ulcer adverse event was twice as high in the placebo vs. active arm (5.9% vs. 2.9%, P = 0.02), but there were no differences in the proportions with ≥1 clinical examination during which perianal or groin ulcers were identified.
Tenofovir in daily oral FTC/TDF PrEP may reduce the occurrence of ulcers in individuals with HSV-2 infection but does not protect against HSV-2 incidence among MSM.
Albert Liu and colleagues report early experiences with uptake and delivery of pre-exposure prophylaxis(PrEP)for HIV prevention in three different settings in San Francisco. PrEP can be an important component of a comprehensive HIV prevention program and can complement efforts to increase HIV testing, linkage to care, and early initiation of antiretroviral therapy.
Please see later in the article for the Editors' Summary
Pre-exposure prophylaxis (PrEP) trials using tenofovir-based regimens have demonstrated that high levels of adherence are required to evaluate efficacy; the incorporation of objective biomarkers of adherence in trial design has been essential to interpretation, given the inaccuracy of self-report. Antiretroviral measurements in scalp hair have been useful as a marker of long-term exposure in the HIV treatment setting, and hair samples are relatively easy and inexpensive to collect, transport, and store for analysis. To evaluate the relationship between dose and tenofovir concentrations in hair, we examined the dose proportionality of tenofovir in hair in healthy, HIV-uninfected adults.
A phase I, crossover pharmacokinetic study was performed in 24 HIV-negative adults receiving directly-observed oral tenofovir tablets administered 2, 4, and 7 doses/week for 6 weeks, with a ≥3-week break between periods. Small samples of hair were collected after each six-week period and analyzed for tenofovir concentrations. Geometric-mean-ratios compared levels between each pair of dosing conditions. Intensive plasma pharmacokinetic studies were performed during the daily-dosing period to calculate areas-under-the-time-concentration curves (AUCs).
Over 90% of doses were observed per protocol. Median tenofovir concentrations in hair increased monotonically with dose. A log-linear relationship was seen between dose and hair levels, with an estimated 76% (95% CI 60–93%) increase in hair level per 2-fold dose increase. Tenofovir plasma AUCs modestly predicted drug concentrations in hair.
This study found a strong linear relationship between frequency of dosing and tenofovir levels in scalp hair. The analysis of quantitative drug levels in hair has the potential to improve adherence measurement in the PrEP field and may be helpful in determining exposure thresholds for protection and explaining failures in PrEP trials. Hair measures for adherence monitoring may also facilitate adherence measurement in real-world settings and merit further investigation in upcoming PrEP implementation studies and programs.
Preexposure prophylaxis (PrEP) with emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) reduced HIV acquisition in the iPrEx trial among men who have sex with men and transgender women. Self-reported sexual risk behavior decreased overall, but may be affected by reporting bias. We evaluated potential risk compensation using biomarkers of sexual risk behavior.
Design and methods
Sexual practices were assessed at baseline and quarterly thereafter; perceived treatment assignment and PrEP efficacy beliefs were assessed at 12 weeks. Among participants with ≥1 follow-up behavioral assessment, sexual behavior, syphilis, and HIV infection were compared by perceived treatment assignment, actual treatment assignment, and perceived PrEP efficacy.
Overall, acute HIV infection and syphilis decreased during follow-up. Compared with participants believing they were receiving placebo, participants believing they were receiving FTC/TDF reported more receptive anal intercourse partners prior to initiating drug (12.8 vs. 7.7, P = 0.04). Belief in receiving FTC/TDF was not associated with an increase in receptive anal intercourse with no condom (ncRAI) from baseline through follow-up (risk ratio [RR] 0.9, 95% confidence interval [CI]: 0.6–1.4; P = 0.75), nor with a decrease after stopping study drug (RR 0.8, 95% CI: 0.5–1.3; P = 0.46). In the placebo arm, there were trends toward lower HIV incidence among participants believing they were receiving FTC/TDF (incidence rate ratio [IRR] 0.8, 95% CI: 0.4–1.8; P = 0.26) and also believing it was highly effective (IRR 0.5, 95% CI: 0.1–1.7; P = 0.12).
There was no evidence of sexual risk compensation in iPrEx. Participants believing they were receiving FTC/TDF had more partners prior to initiating drug, suggesting that risk behavior was not a consequence of PrEP use.
Intermittent dosing of pre-exposure prophylaxis (iPrEP) has potential to decrease costs, improve adherence, and minimize toxicity. Practical event-based dosing of iPrEP requires men who have sex with men (MSM) to be sexually active on fewer than 3 days each week and plan for sexual activity. MSM who may be most suitable for event-based dosing were older, more educated, more frequently used sexual networking websites, and more often reported that their last sexual encounter was not with a committed partner. A substantial proportion of these MSM endorse high-risk sexual activity, and event-based iPrEP may best target this population.
intermittent pre-exposure prophylaxis (iPrEP); pre-exposure prophylaxis (PrEP); event-based dosing; men-who-have-sex-with-men (MSM); HIV; sexual frequency; sexual planning
Drug concentrations associated with protection from HIV-1 acquisition have not been determined. This study evaluated drug concentrations among men who have sex with men in a substudy of the iPrEx trial,(1) a randomized placebo controlled trial of daily oral emtricitabine/tenofovir disoproxil fumarate pre-exposure prophylaxis (PrEP). Any detectable drug in blood plasma and viably cryopreserved peripheral blood mononuclear cells (vPBMCs) was less frequent in HIV-infected cases at the visit when HIV was first discovered compared with controls at the matched time point of the study (8% vs 44%, P<0.001) and in the 90 days prior to that visit (11% vs 51%, P<0.001). An intracellular tenofovir-diphosphate (TFV-DP) concentration of 16 fmol per million vPBMCs was associated with a 90% reduction in HIV acquisition relative to the placebo arm. Directly observed dosing in a separate study, STRAND, yielded TFV-DP concentrations that, when analyzed with this iPrEx model, corresponded with HIV-1 risk reduction of 76% for 2 doses per week, 96% for 4 doses per week, 99% for 7 doses per week. Prophylactic benefits were observed over a range of doses and drug concentrations, suggesting ways to optimize PrEP regimens for this population.
Transient HIV infections have been invoked to account for the cellular immune responses detected in highly virus-exposed individuals who have remained HIV seronegative. We tested for very low levels of HIV RNA in 524 seronegative plasma samples from 311 highly exposed women and men from 3 longitudinal HIV cohorts.
2073 transcription mediated amplification (TMA) HIV RNA tests were performed for an average of 3.95 TMA assays per plasma sample. Quadruplicate TMA assays, analyzing a total of 2 ml of plasma, provided an estimated sensitivity of 3.5 HIV RNA copies/ml.
Four samples from subjects who did not sero-convert within the following six months were positive for HIV RNA. For one sample, human polymorphism DNA analysis indicated a sample mix up. Borderline HIV RNA detection signals were detected for the other three positive samples and further replicate TMA testing yielded no positive results. Nested PCR assays (n=254) for HIV proviral DNA on PBMC from these 3 subjects were negative.
Transient viremia was not reproducibly detected in highly HIV exposed seronegative men and women. If transient infections do occur, plasma HIV RNA levels may remain below the detection limits of the sensitive assay used here, be of very short duration, or viral replication may be restricted to mucosal surfaces or their draining lymphoid tissues.
Pre-exposure prophylaxis (PrEP) trials are evaluating regimens containing tenofovir-disoproxil fumarate (TDF) for HIV prevention. We determined the baseline prevalence of low bone mineral density (BMD) and the effect of TDF on BMD in men who have sex with men (MSM) in a PrEP trial in San Francisco.
We evaluated 1) the prevalence of low BMD using Dual Energy X-ray Absorptiometry (DEXA) in a baseline cohort of 210 HIV-uninfected MSM who screened for a randomized clinical trial of daily TDF vs. placebo, and 2) the effects of TDF on BMD in a longitudinal cohort of 184 enrolled men. Half began study drug after a 9-month delay to evaluate changes in risk behavior associated with pill-use. At baseline, 20 participants (10%) had low BMD (Z score≤−2.0 at the L2–L4 spine, total hip, or femoral neck). Low BMD was associated with amphetamine (OR = 5.86, 95% CI 1.70–20.20) and inhalant (OR = 4.57, 95% CI 1.32–15.81) use; men taking multivitamins, calcium, or vitamin D were less likely to have low BMD at baseline (OR = 0.26, 95% CI 0.10–0.71). In the longitudinal analysis, there was a 1.1% net decrease in mean BMD in the TDF vs. the pre-treatment/placebo group at the femoral neck (95% CI 0.4–1.9%), 0.8% net decline at the total hip (95% CI 0.3–1.3%), and 0.7% at the L2–L4 spine (95% CI −0.1–1.5%). At 24 months, 13% vs. 6% of participants experienced >5% BMD loss at the femoral neck in the TDF vs. placebo groups (p = 0.13).
Ten percent of HIV-negative MSM had low BMD at baseline. TDF use resulted in a small but statistically significant decline in BMD at the total hip and femoral neck. Larger studies with longer follow-up are needed to determine the trajectory of BMD changes and any association with clinical fractures.
Antiretroviral chemoprophylaxis before exposure is a promising approach for the prevention of human immunodeficiency virus (HIV) acquisition.
We randomly assigned 2499 HIV-seronegative men or transgender women who have sex with men to receive a combination of two oral antiretroviral drugs, emtricitabine and tenofovir disoproxil fumarate (FTC–TDF), or placebo once daily. All subjects received HIV testing, risk-reduction counseling, condoms, and management of sexually transmitted infections.
The study subjects were followed for 3324 person-years (median, 1.2 years; maximum, 2.8 years). Of these subjects, 10 were found to have been infected with HIV at enrollment, and 100 became infected during follow-up (36 in the FTC–TDF group and 64 in the placebo group), indicating a 44% reduction in the incidence of HIV (95% confidence interval, 15 to 63; P = 0.005). In the FTC–TDF group, the study drug was detected in 22 of 43 of seronegative subjects (51%) and in 3 of 34 HIV-infected subjects (9%) (P<0.001). Nausea was reported more frequently during the first 4 weeks in the FTC–TDF group than in the placebo group (P<0.001). The two groups had similar rates of serious adverse events (P = 0.57).
Oral FTC–TDF provided protection against the acquisition of HIV infection among the subjects. Detectable blood levels strongly correlated with the prophylactic effect. (Funded by the National Institutes of Health and the Bill and Melinda Gates Foundation; ClinicalTrials.gov number, NCT00458393.)
Pre-exposure prophylaxis (PrEP) for HIV prevention is a promising experimental approach currently being tested globally. A number of PrEP trials are evaluating the safety and effectiveness of PrEP in men who have sex with men (MSM) and other populations at risk for HIV, and results will be available from this first generation of efficacy trials over the next few years. Here we review the rationale for orally-administered antiretrovirals for prevention, and outline issues the first generation trials will address as well as questions that may be addressed in future studies. We also describe the rationale for combination prevention approaches that may combine PrEP with other prevention modalities as part of a larger prevention package.
Pre-exposure prophylaxis; Clinical trials; HIV prevention; Combination prevention
Tenofovir disoproxil fumarate (TDF) pre-exposure prophylaxis decreases sexual acquisition of HIV infection. We sought to evaluate the renal safety of TDF in HIV-uninfected persons.
Design and methods:
The Iniciativa Profilaxis Pre-Exposición (iPrEx) study randomly assigned 2499 HIV-seronegative men and transgender women who have sex with men (MSM) to receive oral daily TDF coformulated with emtricitabine (FTC/TDF) or placebo. Serum creatinine and phosphorus during randomized treatment and after discontinuation were measured, and creatinine clearance (CrCl) was estimated by the Cockcroft–Gault equation. Indicators of proximal renal tubulopathy (fractional excretion of phosphorus and uric acid, urine protein, and glucose) were measured in a substudy.
There was a small but statistically significant decrease in CrCl from baseline in the active arm, compared to placebo, which was first observed at week 4 (mean change: −2.4 vs. −1.1 ml/min; P = 0.02), persisted through the last on-treatment visit (mean change: +0.3 vs. +1.8 ml/min; P = 0.02), and resolved after stopping pre-exposure prophylaxis (mean change: −0.1 vs. 0.0 ml/min; P = 0.83). The effect was confirmed when stratifying by drug detection. The effect of FTC/TDF on CrCl did not vary by race, age, or history of hypertension. There was no difference in serum phosphate trends between the treatment arms. In the substudy, two participants receiving placebo had indicators of tubulopathy.
In HIV-seronegative MSM, randomization to FTC/TDF was associated with a very mild nonprogressive decrease in CrCl that was reversible and managed with routine serum creatinine monitoring.
chemoprophylaxis; HIV prevention; MSM; pre-exposure prophylaxis; renal; side effects; tenofovir
Supplemental Digital Content is Available in the Text.
The efficacy of pre-exposure prophylaxis (PrEP) in HIV will diminish with poor adherence; pharmacologic measures of drug exposure have proven critical to PrEP trial interpretation. We assessed drug exposure in hair against other pharmacologic and more routinely used measures to assess pill-taking.
Participants were randomized to placebo, daily PrEP, or intermittent PrEP to evaluate safety and tolerability of daily versus intermittent tenofovir/emtricitabine (TFV/FTC) in 2 phase II PrEP clinical trials conducted in Africa. Different measures of drug exposure, including self-report, medication event monitoring system (MEMS)-caps openings, and TFV/FTC levels in hair and other biomatrices were compared.
At weeks 8 and 16, self-reported pill-taking, MEMS-caps openings, and TFV/FTC levels in hair, plasma, and peripheral blood mononuclear cells (PBMCs) were measured. Regression models evaluated predictors of TFV/FTC concentrations in the 3 biomatrices; correlation coefficients between pharmacologic and nonpharmacologic measures were calculated. Both trials were registered on ClinicalTrials.gov (NCT00931346/NCT00971230).
Hair collection was highly feasible and acceptable (100% in week 8; 96% in week 16). In multivariate analysis, strong associations were seen between pharmacologic measures and MEMS-caps openings (all P < 0.001); self-report was only weakly associated with pharmacologic measures. TFV/FTC hair concentrations were significantly correlated with levels in plasma and PBMCs (correlation coefficients, 0.41–0.86, all P < 0.001).
Measuring TFV/FTC exposure in small hair samples in African PrEP trials was feasible and acceptable. Hair levels correlated strongly with PBMC, plasma concentrations, and MEMS-caps openings. As in other PrEP trials, self-report was the weakest measure of exposure. Further study of hair TFV/FTC levels in PrEP trials and demonstration projects to assess adherence/exposure is warranted.
tenofovir; pre-exposure prophylaxis (PrEP); hair; self-report; HIV; medication adherence