Pharmacokinetics of oral tenofovir disoproxil fumarate in pregnancy and lactation: a systematic review

Challenges, risks, and opportunities of antiretroviral drugs in women of reproductive potential

INTRODUCTION

The HIV/AIDS epidemic has been one of the greatest challenges in global health, significantly affecting women of reproductive potential. Considerable advances in antiretroviral therapy for women living with HIV have contributed to improvements in quality of life, better reproductive and birth outcomes, and a reduced risk of perinatal transmission.

AREAS COVERED

Despite the progress made, persistent challenges in access and adherence to antiretroviral drugs may limit their benefits for some women. More pharmacokinetic and safety studies in pregnant and lactating women are urgently needed, as are prospective surveillance systems to evaluate associations between fetal and infant antiretroviral exposures, drug-drug interactions, and pregnancy outcomes.

EXPERT OPINION

Multipurpose technologies, such as combined HIV and other STI or unintended pregnancy prevention, and innovative delivery methods, such as the development of long-acting antiretrovirals, have the potential to reduce adherence challenges and enhance quality of life for women with HIV. Parallel advances in drug safety testing and surveillance are needed to ensure the health and safety of women with or at risk for HIV and children at risk for perinatal transmission.

Profiling the Interaction between Human Serum Albumin and Clinically Relevant HIV Reverse Transcriptase Inhibitors

Tenofovir (TFV) is the active form of the prodrugs tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF), both clinically prescribed as HIV reverse transcriptase inhibitors. The biophysical interactions between these compounds and human serum albumin (HSA), the primary carrier of exogenous compounds in the human bloodstream, have not yet been thoroughly characterized. Thus, the present study reports the interaction profile between HSA and TFV, TDF, and TAF via UV-Vis, steady-state, and time-resolved fluorescence techniques combined with isothermal titration calorimetry (ITC) and in silico calculations. A spontaneous interaction in the ground state, which does not perturb the microenvironment close to the Trp-214 residue, is classified as weak. In the case of HSA/TFV and HSA/TDF, the binding is both enthalpically and entropically driven, while for HSA/TAF, the binding is only entropically dominated. The binding constant (Ka) and thermodynamic parameters obtained via ITC assays agree with those obtained using steady-state fluorescence quenching measurements, reinforcing the reliability of the data. The small internal cavity known as site I is probably the main binding pocket for TFV due to the low steric volume of the drug. In contrast, most external sites (II and III) can better accommodate TAF due to the high steric volume of this prodrug. The cross-docking approach corroborated experimental drug-displacement assays, indicating that the binding affinity of TFV and TAF might be impacted by the presence of different compounds bound to albumin. Overall, the weak binding capacity of albumin to TFV, TDF, and TAF is one of the main factors for the low residence time of these antiretrovirals in the human bloodstream; however, positive cooperativity for TAF and TDF was detected in the presence of some drugs, which might improve their residence time (pharmacokinetic profile).

Comparing a point-of-care urine tenofovir lateral flow assay to self-reported adherence and their associations with viral load suppression among adults on antiretroviral therapy

BACKGROUND

Point-of-care (POC) lateral flow assays (LFA) to detect tenofovir (TFV) in urine have been developed to measure short-term ART adherence. Limited data exist from people living with HIV in routine care.

METHODS

Adults on TFV-containing regimens, having a routine viral load (VL) at an HIV clinic in Cape Town, South Africa were enrolled in a cross-sectional study. Patients recalled missed ART doses in the past three and 7 days and urine was tested using a POC TFV LFA. VL on the day was abstracted from medical records.

RESULTS

Among 314 participants, 293 (93%) had VL <1000 copies/mL, 20 (6%) had no TFV detected and 24 (8%) reported ≥1 missed dose in the past 3 days. Agreement between VL ≥1000 and undetectable TFV was higher compared to 3-day recall of ≥1 missed dose (Kappa 0.504 vs. 0.163, p = 0.015). The AUC to detect VL ≥1000 was 0.747 (95% CI 0.637-0.856) for undetectable TFV. This was statistically significantly better than for 7-day recall (0.571 95% CI 0.476-0.666, p = 0.040) but not for 3-day recall (0.587 95% CI 0.492-0.681, p = 0.071) of ≥1 missed dose.

CONCLUSION

In this largely virally suppressed cohort, TFV in urine had better agreement with VL than self-reported adherence and was a better predictor of viraemia on two of three self-report measures. Used in combination with VL, the POC urine TFV LFA could flag patients with viraemia in the presence of ART. Further research is needed to understand the potential application in different populations on ART, including pregnant women.

Pharmacokinetics of Antiretroviral Agents in Pregnant Individuals Living With HIV: Current Status and Considerations for Study Design and Interpretation

Determining the appropriate dosing regimens of antiretroviral (ARV) drugs for pregnant individuals living with HIV-1 infection is critical to maximize maternal health and prevent perinatal HIV transmission. Throughout pregnancy, pharmacokinetics (PK) of ARVs can be significantly altered due to physiological, anatomic, and metabolic changes. As such, conducting PK studies of ARVs during pregnancy is crucial to optimize dosing regimens. In this article, we summarize available data, key issues, challenges, and considerations in interpreting results of ARV PK studies in pregnant individuals. Discussion topics include the choice of the reference population (postpartum vs historical control), pregnancy trimester-dependent changes in ARV PK, effects of pregnancy on once- versus twice-daily dosing, factors to consider for ARVs that are administered with a PK booster such as ritonavir and cobicistat, and considerations when evaluating the effects of pregnancy on unbound ARV concentrations. Common approaches for the translation of the results into clinical recommendations and rationales and considerations when making clinical recommendations are summarized. Currently, limited PK data in pregnancy are available with long-acting ARVs. Collection of PK data to characterize the PK profile of long-acting ARVs is an important goal shared by many stakeholders.

Plasma and breast milk pharmacokinetics of tenofovir alafenamide in mothers with chronic hepatitis B infection

BACKGROUND

Antenatal antiviral therapy (AVT) is effective in preventing mother-to-child transmission (MTCT) in chronic hepatitis B (CHB); tenofovir disoproxil fumarate (TDF) is the preferred agent. Tenofovir alafenamide (TAF) is a prodrug of tenofovir (TFV) similar to TDF, with improved bone and renal safety. There are no data on TAF breast milk pharmacokinetics and exposure to breastfeeding infants in CHB.

AIM

To assess the pharmacokinetics of TAF/TFV in breastfeeding women with CHB on TAF monotherapy.

METHODS

Pregnant women with CHB requiring AVT commenced TAF 25 mg daily at third trimester or postpartum. Sample collection occurred while breastfeeding and taking TAF for minimum 4 weeks. Maternal blood, breast milk and infant urine samples were collected. Drug concentrations were measured by LCMS/MS analyses using validated methods. Non-compartmental analyses were performed to quantify the pharmacokinetic parameters.

RESULTS

Eight women provided samples. In breast milk and plasma, median TAF half-life was 0.81 and 0.94 h, respectively, and C_max 1.69 and 120.5 ng/ml, respectively. Median maternal breast milk to plasma (M/P) ratio of TAF was 0.029; for and TFV it was 2.809. The relative infant dose of TAF was 0.005% of maternal dose, well below safety threshold of 5-10%. TFV was detectable in three out of seven infant urine samples with median steady-state concentration of 5 ng/ml being 300-2500 times less than reported adult steady-state urine concentrations in those taking TAF and TDF, respectively.

CONCLUSIONS

In this first pharmacokinetic study of TAF monotherapy in breastfeeding women with CHB, concentrations of TAF and TFV were low in breast milk with negligible infant exposure, supporting the use of TAF to prevent MTCT.

Pharmacological approaches to prevent vertical transmission of HIV and HBV

INTRODUCTION

Mother-to-child transmission (MTCT) is mainly responsible for the global pediatric HIV and HBV epidemic. Vertical transmission can be prevented and reduced through a series of interventions at the primary healthcare level, including extensive screening of pregnant women, administration of antivirals or immune-based treatments, counselling on type of delivery and breastfeeding.

AREAS COVERED

In this narrative review, approved therapeutic options for the treatment of pregnant women living with HIV or HBV are discussed with special focus on efficacy and safety profiles of each agent or drug class examined. The search was performed using Medline (via PubMed), Web of Science, and Google Scholar to identify studies assessing vertical transmission of both HIV and HBV.

EXPERT OPINION

Elimination of MTCT of both infections is firmly endorsed by major global commitments and the integration of tailored preventive interventions into maternal and newborn health services is of strategical importance to achieve this critical target. However, further research centered on antiviral-based and immunization trials among pregnant women is urgently needed to mitigate the risk of maternal and neonatal adverse outcomes, effectively prevent transmission to the offspring and finally eliminate the pediatric HIV and HBV epidemic, one of the key global health challenges of our time.

Detectable HIV RNA in late pregnancy associated with low tenofovir hair levels at time of delivery among women living with HIV in the United States

OBJECTIVE

We evaluated peripartum tenofovir (TFV) exposure via hair measures among women living with HIV in the United States.

DESIGN

Observational cohort study.

METHODS

Hair samples were collected at or shortly after childbirth among mothers enrolled in the Surveillance Monitoring for Antiretroviral Therapy Toxicities Study of the Pediatric HIV/AIDS Cohort Study between 6/2014 and 7/2016. Among mothers receiving TFV disoproxil fumarate (TDF)-based regimens during pregnancy, TFV hair concentrations were analyzed using liquid chromatography/tandem mass spectrometry. Weight-normalized TFV concentrations were log10 transformed. Multivariable linear regression assessed correlates of TFV concentrations.

RESULTS

Overall, 121 mothers on TDF-based antiretroviral therapy during pregnancy had hair specimens tested for TFV concentrations and were included in the analysis. Median age at delivery was 31 years [interquartile range (IQR) 26-36]; 71% self-identified as non-Hispanic black, and 10% had unsuppressed viral loads in late pregnancy (HIV RNA ≥ 400 copies/ml). Median time from birth to hair collection was 3 days (IQR 1-14) and median TFV hair concentration was 0.02 ng/mg (IQR 0.01-0.04). In multivariable models, an unsuppressed viral load in late pregnancy was associated with 80% lower adjusted mean peripartum TFV concentrations than pregnancies with viral suppression (95% confidence interval: -90% to -59%, P < 0.001). Use of TDF only in the first trimester and attaining high school graduation were also associated with lower TFV hair concentrations.

CONCLUSION

Unsuppressed viral load during late pregnancy was strongly associated with lower maternal TFV hair concentrations at birth, though viremia was rare. Efforts to improve maternal virological outcomes and eliminate vertical HIV transmission could incorporate drug exposure monitoring using hair or other metrics.

Tenofovir diphosphate concentrations in dried blood spots from pregnant and postpartum adolescent and young women receiving daily observed pre-exposure prophylaxis in sub-Saharan Africa

Background

Intracellular tenofovir diphosphate (TFV-DP) concentration in dried blood spots (DBSs) is used to monitor cumulative pre-exposure prophylaxis (PrEP) adherence. We evaluated TFV-DP in DBSs following daily oral PrEP (emtricitabine 200 mg/tenofovir diphosphate 300 mg) among pregnant and postpartum adolescent girls and young women (AGYW).

Methods

Directly observed PrEP was administered for 12 weeks in a pregnancy (14–24 weeks’ gestation, n = 20) and postpartum (6–12 weeks postpartum, n = 20) group of AGYW aged 16–24 years in sub-Saharan Africa. Weekly DBS TFV-DP was measured by validated liquid chromatography–tandem mass spectrometry assay. Week 12 TFV-DP distributions were compared between groups with Wilcoxon test. Population pharmacokinetic models were fit to estimate steady-state concentrations and create benchmarks for adherence categories. Baseline correlates of TFV-DP were evaluated.

Results

Median age was 20 (IQR, 19–22) years. Of 3360 doses, 3352 (>99%) were directly observed. TFV-DP median (IQR) half-life was 10 (7–12) days in pregnancy and 17 (14–21) days postpartum, with steady state achieved by 5 and 8 weeks, respectively. Observed median (IQR) steady-state TFV-DP was 965 fmol/punch (691–1166) in pregnancy versus 1406 fmol/punch (1053–1859) postpartum (P = .006). Modeled median steady-state TFV-DP was 881 fmol/punch (667–1105) in pregnancy versus 1438 fmol/punch (1178–1919) postpartum. In pooled analysis, baseline creatinine clearance was associated with observed TFV-DP concentrations.

Conclusions

TFV-DP in African AGYW was approximately one-third lower in pregnancy than postpartum. These Population-specific benchmarks can be used to guide PrEP adherence support in pregnant/postpartum African women.

Clinical Trials Registration

NCT03386578

Prevention of mother-to-child transmission of hepatitis B virus: protocol for a one-arm, open-label intervention study to estimate the optimal timing of tenofovir in pregnancy

INTRODUCTION

Hepatitis B virus (HBV) remains a public health threat and the main route of transmission is from mother to child (MTCT). Tenofovir disoproxil fumarate (TDF) treatment can reduce MTCT of HBV although the optimal timing to attain undetectable HBV DNA concentrations at delivery is unknown. This protocol describes the procedures following early initiation of maternal TDF prior to 20 weeks gestation to determine efficacy, safety and feasibility of this approach in a limited-resource setting.

METHODS AND ANALYSES

One hundred and seventy pregnant women from the Thailand-Myanmar border between 12 and <20 weeks gestational age will be enrolled into a one-arm, open-label, TDF treatment study with cessation of TDF 1 month after delivery. Sampling occurs monthly prenatal, at birth and at 1, 2, 4 and 6 months post partum. Measurement of tenofovir concentrations in maternal and cord plasma is anticipated in 10-15 women who have detectable HBV DNA at delivery and matched to 20-30 women with no detectable HBV DNA. Infant HBsAg status will be determined at 2 months of age and HBV DNA confirmed in HBsAg positive cases. Adverse events including risk of flare and adherence, based on pill count and questionnaire, will be monitored. Infants will receive HBV vaccinations at birth, 2, 4 and 6 months and hepatitis B immunoglobulin at birth if the mother is hepatitis B e antigen positive. Infant growth and neurodevelopment at 6 months will be compared with established local norms.

ETHICS AND DISSEMINATION

This study has ethical approval by the Ethics Committee of the Faculty of Tropical Medicine, Mahidol University (FTM ECF-019-06), Johns Hopkins University (IRB no: 00007432), Chiang Mai University (FAM-2559-04227), Oxford Tropical Research Ethics Committee (OxTREC Reference: 49-16) and by the local Tak Community Advisory Board (TCAB-02/REV/2016). The article will be published as an open-access publication.

TRIAL REGISTRATION NUMBER

NCT02995005, Pre-results.

Drug dosing during pregnancy-opportunities for physiologically based pharmacokinetic models

Drugs can have harmful effects on the embryo or the fetus at any point during pregnancy. Not all the damaging effects of intrauterine exposure to drugs are obvious at birth, some may only manifest later in life. Thus, drugs should be prescribed in pregnancy only if the expected benefit to the mother is thought to be greater than the risk to the fetus. Dosing of drugs during pregnancy is often empirically determined and based upon evidence from studies of non-pregnant subjects, which may lead to suboptimal dosing, particularly during the third trimester. This review collates examples of drugs with known recommendations for dose adjustment during pregnancy, in addition to providing an example of the potential use of PBPK models in dose adjustment recommendation during pregnancy within the context of drug-drug interactions. For many drugs, such as antidepressants and antiretroviral drugs, dose adjustment has been recommended based on pharmacokinetic studies demonstrating a reduction in drug concentrations. However, there is relatively limited (and sometimes inconsistent) information regarding the clinical impact of these pharmacokinetic changes during pregnancy and the effect of subsequent dose adjustments. Examples of using pregnancy PBPK models to predict feto-maternal drug exposures and their applications to facilitate and guide dose assessment throughout gestation are discussed.