Characterizing HIV-Preventive, Plasma Tenofovir Concentrations-A Pooled Participant-level Data Analysis From Human Immunodeficiency Virus Preexposure Prophylaxis Clinical Trials

Adherence and HIV Protection Thresholds for Emtricitabine and Tenofovir Disoproxil Fumarate Preexposure Prophylaxis among Cisgender Women: A Systematic Review

PURPOSE OF REVIEW

Adherence-concentration-efficacy benchmarks have not been fully characterized for cisgender women using emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) oral daily pre-exposure prophylaxis (PrEP) for HIV prevention.

RECENT FINDINGS

We conducted a systematic review to investigate current evidence on the adherence-concentration-efficacy relationship of tenofovir-diphosphate (TFV-DP) derived from FTC/TDF PrEP in dried blood spots (DBS) and peripheral mononuclear cells (PBMC) in cisgender women without HIV, including during pregnancy. We searched for completed and ongoing studies published before May 2024 in PubMed, Embase, Cochrane Library, CINAHL, and clinicaltrial.gov.  Overall, 11 studies assessing adherence benchmarks focusing on (n = 5) or involving (n = 6) cisgender women were included. Women-specific median steady-state TFV-DP concentration for daily dosing ranged from 17 to 51 fmol/106 in PBMC and 1389 to 1685 fmol/punch in DBS in non-pregnant women; 50 to 71 fmol/106 in PBMC and 583 to 965 fmol/punch in DBS in pregnant women; and 618 to 1406 fmol/punch in DBS in postpartum women. DBS TFV-DP levels were 14-43% lower in pregnancy versus postpartum or non-pregnant periods, but PBMC TFV-DP levels appear to be comparable. Clinical and modeling studies demonstrate effective HIV protection for women taking at least four doses/week of oral TDF-based PrEP, and emerging evidence suggests that systemic drug levels are more likely to be predictive of efficacy than local tissue levels at the site of exposure. The preponderance of emerging evidence points to comparable efficacy and similar adherence requirement for women as men among those with detectable drug levels, although there was an indication that the highest achievable efficacy may be reached at a lower adherence level in men than women. In this review, we found evidence that women-specific TFV-DP adherence benchmarks in DBS and PBMC are within range of US-based historical thresholds derived from healthy men and women. Emerging evidence suggests that imperfect but adequate adherence to oral FTC/TDF PrEP with at least four doses/week provides sufficient HIV protection in cisgender women as it does in MSM, but more data are still needed to refine intrinsic achievable efficacy estimates for cisgender women.

HIV Preexposure Prophylaxis With Emtricitabine and Tenofovir Disoproxil Fumarate Among Cisgender Women

Importance

Emtricitabine and tenofovir disoproxil fumarate (F/TDF) for HIV preexposure prophylaxis (PrEP) is highly effective in cisgender men who have sex with men (MSM) when adherence is high (>4 doses/week). Real-world effectiveness and adherence with F/TDF for PrEP in cisgender women is less well characterized.

Objective

To characterize the effectiveness of F/TDF for PrEP and its relationship with adherence in cisgender women.

Design, Setting, and Participants

Data were pooled from 11 F/TDF PrEP postapproval studies conducted in 6 countries that included 6296 cisgender women aged 15 to 69 years conducted from 2012 to 2020. HIV incidence was evaluated according to adherence level measured objectively (tenofovir diphosphate concentration in dried blood spots or tenofovir concentration in plasma; n = 288) and subjectively (electronic pill cap monitoring, pill counts, self-report, and study-reported adherence scale; n = 2954) using group-based trajectory modeling.

Exposures

F/TDF prescribed orally once a day. HIV incidence was analyzed in subgroups based on adherence trajectory.

Main Outcomes and Measures

HIV incidence.

Results

Of the 6296 participants, 46% were from Kenya, 28% were from South Africa, 21% were from India, 2.9% were from Uganda, 1.6% were from Botswana, and 0.8% were from the US. The mean (SD) age at PrEP initiation across all studies was 25 (7) years, with 61% of participants being younger than 25 years. The overall HIV incidence was 0.72 per 100 person-years (95% CI, 0.51-1.01; 32 incident HIV diagnoses among 6296 participants). Four distinct groups of adherence trajectories were identified: consistently daily (7 doses/week), consistently high (4-6 doses/week), high but declining (from a mean of 4-6 doses/week and then declining), and consistently low (less than 2 doses/week). None of the 498 women with consistently daily adherence acquired HIV. Only 1 of the 658 women with consistently high adherence acquired HIV (incidence rate, 0.13/100 person-years [95% CI, 0.02-0.92]). The incidence rate was 0.49 per 100 person-years (95% CI, 0.22-1.08) in the high but declining adherence group (n = 1166) and 1.27 per 100 person-years (95% CI, 0.53-3.04) in the consistently low adherence group (n = 632).

Conclusions and Relevance

In a pooled analysis of 11 postapproval studies of F/TDF for PrEP among cisgender women, overall HIV incidence was 0.72 per 100 person-years; individuals with consistently daily or consistently high adherence (4-6 doses/week) to PrEP experienced very low HIV incidence.

A multicompartment population PK model to predict tenofovir and emtricitabine mucosal tissue concentrations for HIV prevention

A priori use of mathematical modeling and simulation to predict outcomes from incomplete adherence or reduced frequency dosing strategies may mitigate the risk of clinical trial failure with HIV pre-exposure prophylaxis regimens. We developed a semi-physiologic population pharmacokinetic model for two antiretrovirals and their active intracellular metabolites in three mucosal tissues using pharmacokinetic data from a phase I, dose-ranging study. Healthy female volunteers were given a single oral dose of tenofovir disoproxil fumarate (150, 300, or 600 mg) or emtricitabine (100, 200, or 400 mg). Simultaneous co-modeling of all data was performed on a Linux cluster. A 16 compartment, bolus input, linear kinetic model best described the data, containing 986 observations in 23 individuals across three matrices and four analytes. Combined with a defined efficacious concentration target in mucosal tissues, this model can be used to optimize the dose and dosing frequency through Monte-Carlo simulations.

Model-based predictions of protective HIV pre-exposure prophylaxis adherence levels in cisgender women

Most human immunodeficiency virus (HIV) infections occur in cisgender women in resource-limited settings. In women, self-protection with emtricitabine/tenofovir disoproxil fumarate pre-exposure prophylaxis (FTC/TDF-PrEP) constitutes a major pillar of HIV prevention. However, clinical trials in women had inconsistent outcomes, sparking uncertainty about adherence requirements and reluctance in evaluating on-demand regimens. We analyzed data from published FTC/TDF-PrEP trials to establish efficacy ranges in cisgender women. In a 'bottom-up' approach, we modeled hypotheses in the context of risk-group-specific, adherence-efficacy profiles and challenged those hypotheses with clinical data. We found that different clinical outcomes were related to the proportion of women taking the product, allowing coherent interpretation of the data. Our analysis showed that 90% protection was achieved when women took some product. We found that hypotheses of putative male/female differences were either not impactful or statistically inconsistent with clinical data. We propose that differing clinical outcomes could arise from pill-taking behavior rather than biological factors driving specific adherence requirements in cisgender women.

Clinical trial simulation to evaluate tenofovir disoproxil fumarate/emtricitabine HIV pre-exposure prophylaxis dosing during pregnancy

Objective

To evaluate upward-adjustment of tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC) pre-exposure prophylaxis (PrEP) dosing during pregnancy in order to maintain target plasma concentrations associated with HIV protection.

Design

Population pharmacokinetic (PK) modeling and clinical trial simulation (CTS).

Material and methods

We developed population pharmacokinetic models for TFV and FTC using data from the Partners Demonstration Project and a PK study of TDF/FTC among cisgender women by Coleman et al., and performed an in-silico simulation. Pregnancy-trimester was identified as a significant covariate on apparent clearance in the optimized final model. We simulated 1,000 pregnant individuals starting standard daily oral TDF/FTC (300 mg/200 mg) prior to pregnancy. Upon becoming pregnant, simulated patients were split into two study arms: one continuing standard-dose and the other receiving double standard-dose throughout pregnancy.

Results

Standard-dose trough TFV concentrations were significantly lower in pregnancy compared to pre-pregnancy, with 34.0%, 43.8%, and 65.1% of trough plasma concentrations below the lower bound of expected trough concentrations presumed to be the protective threshold in the 1st, 2nd, and 3rd trimesters, respectively. By comparison, in the simulated double-dose group, 10.7%, 14.4%, and 27.8% of trough concentrations fell below the estimated protective thresholds in the 1st, 2nd, and 3rd trimesters, respectively. The FTC trough plasma concentration during pregnancy was also lower than pre-pregnancy, with 45.2% of the steady-state trough concentrations below the estimated protective trough concentrations of FTC. In the pregnancy-adjusted double-dose group, 24.1% of trough plasma concentrations were lower than protective levels.

Conclusions

Our simulation shows >50% of research participants on standard dosing would have 3rd trimester trough plasma TFV concentrations below levels associated with protection. This simulation provides the quantitative basis for the design of prospective TDF/FTC studies during pregnancy to evaluate the safety and appropriateness of pregnancy-adjusted dosing.

Factors that influence adolescent girls and young women's re-initiation or complete discontinuation from daily oral PrEP use: a qualitative study from Eastern Cape Province, South Africa

INTRODUCTION

Adolescent girls and young women (AGYW) face barriers that jeopardize their prevention-effective use of daily oral pre-exposure prophylaxis (PrEP). We sought to understand factors that influence AGYW's prolonged breaks in PrEP use, and their decisions to re-initiate or discontinue using PrEP in the context of a community-based adherence support intervention.

METHODS

In-depth interviews (IDIs) were conducted between December 2019 and April 2021 with purposively selected AGYW (aged 16-25) enrolled in the Community PrEP Study (CPS) in Buffalo City Metro Health District, Eastern Cape Province, South Africa. AGYW were offered monthly PrEP for 24 months at two community-based study sites. Interview guides were informed by the Information-Motivation-Behavioural Skills Model, and data were analysed using illustrative code reports and a case analysis.

RESULTS

A total of 603 participants were enrolled and initiated on PrEP in the parent study. Fifty-three IDIs were conducted with 50 CPS participants. Findings revealed that external factors (e.g. local movement, school holidays and medication side-effects) and social conflicts (e.g. discretion and partner mistrust) directly influenced breaks in PrEP usage. A decrease in one's self-perception of HIV risk prolonged the duration of these "PrEP breaks." Once PrEP refill visits were missed, some AGYW delayed returning for refills out of fear of being scolded by study staff. The differences between those participants who eventually re-initiated PrEP and those who disengaged from PrEP use can be attributed to social support and encouragement, level of familiarity with PrEP, risk perceptions, self-initiated discussions with staff and diminishing side effects.

CONCLUSIONS

Despite implementing a community-based PrEP delivery platform and behavioural intervention that included support for daily oral PrEP adherence and disclosure, participants struggled with consistent daily oral PrEP use. Unpredictable life events, including local movement and schooling schedules, in addition to being judged for their perceived behaviours, pose a challenge for consistent pill pick-up for AGYW and habit formation. Long-acting injectable PrEP may mitigate a number of these external barriers. Interventions that integrate long-term planning skills, how to navigate existing social judgements and how to access sources of social support may further improve habit formation for PrEP use, regardless of its formulation.

Human Immunodeficiency Virus Seroconversion Among Men Who Have Sex With Men Who Use Event-Driven or Daily Oral Pre-Exposure Prophylaxis (CohMSM-PrEP): A Multi-Country Demonstration Study From West Africa

BACKGROUND

Data on human immunodeficiency virus (HIV) seroconversion among men who have sex with men (MSM) using pre-exposure prophylaxis (PrEP) in West Africa are needed. This study aimed to document HIV seroconversion and associated determinants, PrEP adherence, plasma drug concentrations, and HIV drug resistance in MSM using event-driven or daily PrEP in Burkina Faso, Côte d'Ivoire, Mali, and Togo.

METHODS

A prospective cohort study was conducted in 2017-2021 among HIV-seronegative MSM aged 18 or over who were at high risk of HIV infection. Participants could choose between event-driven and daily PrEP, switch regimens, and discontinue or restart PrEP. The determinants of HIV incidence were investigated using a multivariate mixed-effects Poisson regression analysis.

RESULTS

A total of 647 participants were followed for a total time of 1229.3 person-years. Of 5371 visits, event-driven PrEP was chosen in 3873 (72.1%), and daily PrEP in 1400 (26.1%). HIV incidence was 2.4 per 100 person-years (95% confidence interval [CI] 1.5-3.6) for event-driven PrEP, and 0.6 per 100 person-years (95% CI .1-2.3) for daily PrEP (adjusted incidence rate ratio 4.40, 95% CI 1.00-19.36, P = .050). Adequate adherence was lower with event-driven than daily PrEP (44.3% vs 74.9%, P < .001). Plasma drug concentrations were undetectable in 92 (97.9%) of the 94 measures taken for 23 participants who seroconverted. Only 1 participant had resistance to PrEP drugs.

CONCLUSIONS

HIV seroconversions mainly occurred in participants who chose event-driven PrEP. The study's data highlighted major difficulties with adherence to this regimen. Improving adherence to event-driven PrEP constitutes a major research and public health priority in this context.

Pharmacokinetic Model of Tenofovir and Emtricitabine and Their Intracellular Metabolites in Patients in the ANRS 134-COPHAR 3 Trial Using Dose Records

Tenofovir (TFV) and emtricitabine (FTC) are part of the recommended highly active antiretroviral therapy (ART). Both molecules show a large interindividual pharmacokinetic (PK) variability. Here, we modeled the concentrations of plasma TFV and FTC and their intracellular metabolites (TFV diphosphate [TFV-DP] and FTC triphosphate [FTC-TP]) collected after 4 and 24 weeks of treatment in 34 patients from the ANRS 134-COPHAR 3 trial. These patients received daily (QD) atazanavir (300 mg), ritonavir (100 mg), and a fixed-dose combination of coformulated TFV disoproxil fumarate (300 mg) and FTC (200 mg). Dosing history was collected using a medication event monitoring system. A three-compartment model with absorption delay (Tlag) was selected to describe the PK of, respectively, TFV/TFV-DP and FTC/FTC-TP. TFV and FTC apparent clearances, 114 L/h (relative standard error [RSE] = 8%) and 18.1 L/h (RSE = 5%), respectively, were found to decrease with age. However, no significant association was found with the polymorphisms ABCC2 rs717620, ABCC4 rs1751034, and ABCB1 rs1045642. The model allows prediction of TFV-DP and FTC-TP concentrations at steady state with alternative regimens.

Episodic Use of Pre-Exposure Prophylaxis Among Young Cisgender Women in Siaya County, Kenya

The concept "seasons of risk" promotes use of pre-exposure prophylaxis (PrEP) only during periods of HIV risk. PrEP guidelines are aligned on daily use in women having vaginal sex during a risk period, and daily use for 28 days after the last potential exposure is recommended. However, when starting a "season of risk," guidelines vary on "time to protection," and unknowns remain in pharmacological research on PrEP protection in this population. During our iterative research on PrEP persistence using photovoice and in-depth interviews, we identified an ineffective pattern of PrEP use based on current guidelines-that is, routine, episodic use-among young cisgender women (YCW) in Siaya County, Kenya. Through same-group (n = 33 participants) and mixed-group (n = 31 participants) photovoice activities with YCW taking PrEP and female peers, participants explained that YCW associate their HIV risk with the sexual behaviors of their male partners who frequently travel from home. PrEP is considered unnecessary when partners are away because of no perceived risk. YCW re-start PrEP on or around the day of their partners' return because of heightened risk perceptions. Among the YCW interviewed (n = 18), nearly all of their partners traveled for about 1 week to 1 month at a time; about one-third of these women reported stopping PrEP during their partners' absence and re-starting it soon before or immediately upon their partners' arrival home. Additional research is critically needed to better inform PrEP guidelines and the decisions adolescent girls and young women make on how to use PrEP based on their risk context. In the interim, counseling on current dosing guidance when stopping and re-starting PrEP within a "season of risk" is needed.

Modeling the Probability of HIV Infection over Time in High-Risk Seronegative Participants Receiving Placebo in Five Randomized Double-Blind Placebo-Controlled HIV Pre-Exposure Prophylaxis Trials: A Patient-Level Pooled Analysis

The World Health Organization recommends pre-exposure prophylaxis (PrEP) for individuals at substantial risk of HIV infection. The aim of this analysis is to quantify the individual risk of HIV infection over time, using a large database of high-risk individuals (n = 5583). We used data from placebo recipients in five phase III PrEP trials: iPrEx, conducted in men who have sex with men and transgender women; VOICE, conducted in young women at high sexual risk; Partners PrEP, conducted in HIV serodiscordant heterosexual couples; TDF2, conducted in high-risk heterosexual men and women; and BTS, conducted in persons who inject drugs. The probability of HIV infection over time was estimated using NONMEM7.4. We identified predictors of HIV risk and found a substantial difference in the risk of infection among and within trial populations, with each study including a mix of low, moderate, and high-risk individuals (p < 0.05). Persons who were female at birth were at a higher risk of HIV infection than people who were male at birth. Final models were integrated in a tool that can assess person-specific risk and simulate cumulative HIV risk over time. These models can be used to optimize future PrEP clinical trials by identifying potential participants at highest risk.