Tenofovir Alafenamide: A Review in Chronic Hepatitis B. Drugs. 2017;77:1017-1028. [PMID: 28493172 DOI: 10.1007/s40265-017-0754-9]

Deviated binding of anti-HBV nucleoside analog E-CFCP-TP to the reverse transcriptase active site attenuates the effect of drug-resistant mutations

While certain human hepatitis B virus-targeting nucleoside analogs (NAs) serve as crucial anti-HBV drugs, HBV yet remains to be a major global health threat. E-CFCP is a 4'-modified and fluoromethylenated NA that exhibits potent antiviral activity against both wild-type and drug-resistant HBVs but less potent against human immunodeficiency virus type-1 (HIV-1). Here, we show that HIV-1 with HBV-associated amino acid substitutions introduced into the RT's dNTP-binding site (N-site) is highly susceptible to E-CFCP. We determined the X-ray structures of HBV-associated HIV-1 RT mutants complexed with DNA:E-CFCP-triphosphate (E-CFCP-TP). The structures revealed that exocyclic fluoromethylene pushes the Met184 sidechain backward, and the resultant enlarged hydrophobic pocket accommodates both the fluoromethylene and 4'-cyano moiety of E-CFCP. Structural comparison with the DNA:dGTP/entecavir-triphosphate complex also indicated that the cyclopentene moiety of the bound E-CFCP-TP is slightly skewed and deviated. This positioning partly corresponds to that of the bound dNTP observed in the HIV-1 RT mutant with drug-resistant mutations F160M/M184V, resulting in the attenuation of the structural effects of F160M/M184V substitutions. These results expand our knowledge of the interactions between NAs and the RT N-site and should help further design antiviral NAs against both HIV-1 and HBV.

Five-year Treatment with Tenofovir Alafenamide Achieves High Rates of Viral Suppression, Alanine Aminotransferase Normalization, and Favorable Bone and Renal Safety in Chinese Chronic Hepatitis B Patients

Background and Aims

After 3-years (144 week) of double-blind treatment in Chinese chronic hepatitis B patients in two ongoing phase 3 studies, tenofovir alafenamide (TAF) showed similar efficacy to tenofovir disoproxil fumarate (TDF), with improved renal and bone safety. In this study, we aimed to report the 5-year results from 2 years into the open-label TAF treatment phase.

Methods

All participants completing the 144-week double-blind treatment were eligible to receive open-label TAF 25 mg once daily up to week 384. Serial analysis of viral suppression (hepatitis B virus DNA <29 IU/mL), alanine aminotransferase normalization, serological responses, and safety outcomes at year 5 (week 240) was performed.

Results

The open-label phase included 93% (311/334) of the enrolled participants, which included 212 who switched from double-blind TAF to open-label TAF (TAF-TAF) and 99 who switched from double-blind TDF to open-label TAF (TDF-TAF). Baseline characteristics were comparable. Week 240 viral suppression rates were similar between groups [93.4% vs. 93.9%; difference: -1.5%, (95% CI: -6.4 to -3.5), p=0.857]. Alanine aminotransferase normalization and serological response rates were higher in the TAF-TAF group than in the TDF-TAF group. The frequencies of adverse events and laboratory abnormalities were low and similar between groups. Both groups had similar small numerical declines from baseline in estimated glomerular filtration rate at year 5 (week 240, -2.85 mL/min vs. -3.29 mL/min, p=0.910). The greater declines in renal and bone parameters in the TDF-TAF group through week 144 improved after switching to TAF.

Conclusions

The 5-year TAF treatment efficacy was high and similar to that of 3-year TDF followed by 2-year TAF in Chinese chronic hepatitis B patients. Favorable effects on bone and renal parameters were sustained with TAF treatment alone and were observed following the switch from TDF to TAF.

Cell-Dependent Activation of ProTide Prodrugs and Its Implications in Antiviral Studies

The ProTide prodrug design is a powerful tool to improve cell permeability and enhance the intracellular activation of nucleotide antiviral analogues. Previous in vitro studies showed that the activation of ProTide prodrugs varied in different cell lines. In the present study, we investigated the activation profiles of two antiviral prodrugs tenofovir alafenamide (TAF) and sofosbuvir (SOF) in five cell lines commonly used in antiviral research, namely, Vero E6, Huh-7, Calu-3, A549, and Caco-2. We found that TAF and SOF were activated in a cell-dependent manner with Vero E6 being the least efficient and Huh-7 being the most efficient cell line for activating the prodrugs. We also demonstrated that TAF was activated at a significantly higher rate than SOF. We further analyzed the protein expressions of the activating enzymes carboxylesterase 1, cathepsin A, histidine triad nucleotide-binding protein 1, and the relevant drug transporters P-glycoprotein and organic anion-transporting polypeptides 1B1 and 1B3 in the cell lines using the proteomics data extracted from the literature and proteome database. The results revealed significant differences in the expression patterns of the enzymes and transporters among the cell lines, which might partially contribute to the observed cell-dependent activation of TAF and SOF. These findings highlight the variability of the abundance of activating enzymes and transporters between cell lines and emphasize the importance of selecting appropriate cell lines for assessing the antiviral efficacy of nucleoside/nucleotide prodrugs.

Asymmetric Synthesis of US-FDA Approved Drugs over Five Years (2016–2020): A Recapitulation of Chirality

Chirality is a major theme in the design, discovery, and development of new drugs. Historically, pharmaceuticals have been synthesized as racemic mixtures. However, the enantiomeric forms of drug molecules have distinct biological properties. One enantiomer may be responsible for the desired therapeutic effect (eutomer), whereas the other may be inactive, interfere with the therapeutic form, or exhibit toxicity (distomer). Classical chemical synthesis usually leads to a racemic mixture unless stereospecific synthesis is employed. To meet the requirements of single-enantiomeric drugs, asymmetric synthesis has evolved at the forefront of drug discovery. Asymmetric synthesis involves the conversion of an achiral starting material into a chiral product. This review emphasizes the methods used for synthesizing FDA-approved chiral drugs during 2016–2020, with a special focus on asymmetric synthesis by means of chiral induction, resolution, or chiral pool.

Organocatalytic asymmetric synthesis of P-stereogenic molecules

P-chirality broadly appears in natural and synthetic functional molecules. The catalytic synthesis of organophosphorus compounds bearing P-stereogenic centers is still challenging, due to the lack of efficient catalytic systems. This review summarizes the key achievements in organocatalytic methodologies for the synthesis of P-stereogenic molecules. Different catalytic systems are emphasized for each strategy class (desymmetrization, kinetic resolution, and dynamic kinetic resolution) with examples cited to illustrate the potential applications of the accessed P-stereogenic organophosphorus compounds.

Over 40 Years of Fosmidomycin Drug Research: A Comprehensive Review and Future Opportunities

To address the continued rise of multi-drug-resistant microorganisms, the development of novel drugs with new modes of action is urgently required. While humans biosynthesize the essential isoprenoid precursors isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) via the established mevalonate pathway, pathogenic protozoa and certain pathogenic eubacteria use the less well-known methylerythritol phosphate pathway for this purpose. Important pathogens using the MEP pathway are, for example, Plasmodium falciparum, Mycobacterium tuberculosis, Pseudomonas aeruginosa and Escherichia coli. The enzymes of that pathway are targets for antiinfective drugs that are exempt from target-related toxicity. 2C-Methyl-D-erythritol 4-phosphate (MEP), the second enzyme of the non-mevalonate pathway, has been established as the molecular target of fosmidomycin, an antibiotic that has so far failed to be approved as an anti-infective drug. This review describes the development and anti-infective properties of a wide range of fosmidomycin derivatives synthesized over the last four decades. Here we discuss the DXR inhibitor pharmacophore, which comprises a metal-binding group, a phosphate or phosphonate moiety and a connecting linker. Furthermore, non-fosmidomycin-based DXRi, bisubstrate inhibitors and several prodrug concepts are described. A comprehensive structure-activity relationship (SAR) of nearly all inhibitor types is presented and some novel opportunities for further drug development of DXR inhibitors are discussed.

A carrier-free metal-organic hybrid nanoassembly with combination anti-viral and hepato-protective activity for hepatitis B treatment

Hepatitis B represents a major global public health burden, which is caused by the hepatitis B virus (HBV) with a high infection rate. Although several anti-HBV drugs have been developed for clinical treatment of hepatitis B, the current therapeutic strategies still suffer from undeniable adverse effects, insufficient efficacy after systemic administration and chronic inflammation. Here, we develop a carrier-free metal-organic hybrid nanoassembly that is co-loaded with tenofovir (TFV), an anti-viral agent and phosphorylated glycyrrhetinic acid (GAP), an anti-inflammatory compound (TFV/GAP/NA) to enhance the anti-HBV effect and alleviate the inflammatory response for hepatitis B treatment. The nanoassembly is easily prepared through the ionic interactions between the anionic phosphonate/phosphate groups from TFV/GAP and the zirconium cation, which has a stable nanostructure and a high drug-loading capacity. The nanoassembly prolongs the circulation time with reduced drug leakage in the blood and elevates drug accumulation in the liver after intravascular administration. After internalization mediated by the GAP ligand-GA receptor interaction, TFV/GAP/NA disassembles by the phosphatase-triggered degradation of the phosphate ester bonds in GAP and releases TFV, GAP and GA within the HBV-positive hepatocytes. The released TFV interferes with the HBV polymerase to inhibit the viral DNA replication, while the released GAP and GA suppress the pro-inflammatory protein expression. In mouse models, treatment with TFV/GAP/NA inhibits HBV production and alleviates inflammation-mediated liver injury.

HBV/HIV Coinfection: Impact on the Development and Clinical Treatment of Liver Diseases

Hepatitis B virus (HBV) infection is a common contributor to chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Approximately 10% of people with human immunodeficiency virus (HIV) also have chronic HBV co-infection, owing to shared transmission routes. HIV/HBV coinfection accelerates the progression of chronic HBV to cirrhosis, end-stage liver disease, or hepatocellular carcinoma compared to chronic HBV mono-infection. HBV/HIV coinfection alters the natural history of hepatitis B and renders the antiviral treatment more complex. In this report, we conducted a critical review on the epidemiology, natural history, and pathogenesis of liver diseases related to HBV/HIV coinfection. We summarized the novel therapeutic options for these coinfected patients.

Diverse synthetic approaches towards C1'-branched acyclic nucleoside phosphonates

Acyclic nucleoside phosphonates (ANPs) represent a significant class of antiviral, anticancer, and antiprotozoal compounds. It is therefore highly desirable to have diverse synthetic routes leading towards these molecules. In the past, many structural modifications were explored, but surprisingly, the field of C1'-branched ANPs has been neglected with only a handful of articles reporting their synthesis. Herein we describe and compare five convenient approaches leading to key synthetic 6-chloropurine ANPs bearing the 9-phosphonomethoxyethyl (PME) moiety branched at the C1' position. These intermediates can be further vastly diversified into target C1'-branched ANPs bearing either natural or unnatural nucleobases. The importance of C1'-branched ANPs is emphasized by their analogy with C1'-substituted cyclic nucleotides (such as remdesivir, a broad-spectrum antiviral agent) and evaluation of their biological activity (e.g. antiviral, antineoplastic, and antiprotozoal) will be a tempting subject of further research.

An original pronucleotide strategy for the simultaneous delivery of two bioactive drugs

The synthesis and in vitro anti-HIV activity of a novel series of phosphoramidate pronucleotides including a S-pivaloyl-2-thioethyl (tBuSATE) group as biolabile phosphate protecting group are reported. Such constructs, obtained through different phosphorus chemistries, are characterized by the association of two different anti-HIV nucleoside analogues linked to the phosphorus atom respectively by the sugar residue and the exocyclic amino function of the nucleobase. In vitro, comparative anti-HIV evaluation demonstrates that such original prodrugs are able to allow the efficient intracellular combination release of a 5'-mononucleotide as well as another nucleoside analogue. In human T4-lymphoblastoid cells, the pronucleotide 1 shows remarkable antiviral activity with an EC₅₀ in the nanomolar range (0.6 ηM) and without additional cytotoxicity. In addition, these two pronucleotide models exhibit higher selectivity index than the equimolar mixture of their constitutive nucleoside analogues opening the way to further studies with regard to the current use of drug combinations.

Distinctive HBV Replication Capacity and Susceptibility to Tenofovir Induced by a Polymerase Point Mutation in Hepatoma Cell Lines and Primary Human Hepatocytes

Tenofovir disoproxil fumarate (TDF) has been regarded as the most potent drug for treating patients with chronic hepatitis B (CHB). However recently, viral mutations associated with tenofovir have been reported. Here, we found a CHB patient with suboptimal response after more than 4 years of TDF treatment. Clonal analysis of hepatitis B virus (HBV) isolated from sequential sera of this patient identified the seven previously reported TDF-resistant mutations (CYELMVI). Interestingly, a threonine to alanine mutation at the 301 amino acid position of the reverse-transcriptase (RT) domain, (rtT301A), was commonly accompanied with CYELMVI at a high rate (72.7%). Since the rtT301A mutation has not been reported yet, we investigated the role of this naturally occurring mutation on the viral replication and susceptibility to tenofovir in various liver cells (hepatoma cells as well as primary human hepatocytes). A cell-based phenotypic assay revealed that the rtT301A mutation dramatically impaired the replication ability with meaningful reduction in sensitivity to tenofovir in hepatoma cell lines. However, attenuated viral replication by the rtT301A mutation was significantly restored in primary human hepatocytes (PHHs). Our findings suggest that the replication capability and drug sensitivity of HBV is different between hepatoma cell lines and PHHs. Therefore, our study emphasizes that validation studies should be performed not only in the liver cancer cell lines but also in the PHHs to understand the exact viral fitness under antiviral pressure in patients.

Nucleos(t)ide Analogues for Reducing Hepatocellular Carcinoma in Chronic Hepatitis B Patients: A Systematic Review and Meta-Analysis

Background/Aims

Studies have shown that nucleos(t)ide analogue (NA) treatment can reduce the risk of hepatocellular carcinoma (HCC) in chronic hepatitis B (CHB) patients, but it is unclear which NA is most effective. We performed a meta-analysis and systematic review comparing the efficacies of NAs in CHB patients.

Methods

We searched literature databases for randomized controlled trials (RCTs) and observational studies that analyzed the hepatic biochemical response, virological response, seroconversion rate, drug resistance rate, and HCC incidence rate in CHB patients treated with NAs. Meta-analyses were performed with RevMan and Stata/SE software.

Results

Twelve cohort studies and one RCT were selected, in which entecavir (ETV), lamivudine (LAM), telbivudine (LdT), and/or tenofovir disoproxil fumarate (TDF) were evaluated in CHB patients. The meta-analysis showed that ETV was superior to LAM with regard to the HCC incidence (p<0.001), biochemical response (p=0.001), virological response (p=0.02), and drug resistance (p<0.001), and ETV was superior to LdT with regard to the virological response (p<0.001) and drug resistance (p<0.001). We found no significant difference between ETV and TDF with regard to the HCC incidence (p=0.08), biochemical response (p=0.39), virological response (p=0.31), serological conversion (p=0.38), or drug resistance (p=0.95). NA-treated patients with pre-existing cirrhosis had a 5.49 times greater incidence of HCC than those without cirrhosis (p<0.001).

Conclusions

ETV or TDF should be used for long-term first-line monotherapy in CHB patients according to the current guidelines. Standardized protocols are needed for future studies of ETV and TDF to facilitate conclusive comparisons. Patients with cirrhosis are at significantly elevated risk for HCC, despite the benefits of NA treatment.

Nucleos(t)ide Analogues for Reducing Hepatocellular Carcinoma in Chronic Hepatitis B Patients: A Systematic Review and Meta-Analysis

Background/Aims

Studies have shown that nucleos(t)ide analogue (NA) treatment can reduce the risk of hepatocellular carcinoma (HCC) in chronic hepatitis B (CHB) patients, but it is unclear which NA is most effective. We performed a meta-analysis and systematic review comparing the efficacies of NAs in CHB patients.

Methods

We searched literature databases for randomized controlled trials (RCTs) and observational studies that analyzed the hepatic biochemical response, virological response, seroconversion rate, drug resistance rate, and HCC incidence rate in CHB patients treated with NAs. Meta-analyses were performed with RevMan and Stata/SE software.

Results

Twelve cohort studies and one RCT were selected, in which entecavir (ETV), lamivudine (LAM), telbivudine (LdT), and/or tenofovir disoproxil fumarate (TDF) were evaluated in CHB patients. The meta-analysis showed that ETV was superior to LAM with regard to the HCC incidence (p<0.001), biochemical response (p=0.001), virological response (p=0.02), and drug resistance (p<0.001), and ETV was superior to LdT with regard to the virological response (p<0.001) and drug resistance (p<0.001). We found no significant difference between ETV and TDF with regard to the HCC incidence (p=0.08), biochemical response (p=0.39), virological response (p=0.31), serological conversion (p=0.38), or drug resistance (p=0.95). NA-treated patients with pre-existing cirrhosis had a 5.49 times greater incidence of HCC than those without cirrhosis (p<0.001).

Conclusions

ETV or TDF should be used for long-term first-line monotherapy in CHB patients according to the current guidelines. Standardized protocols are needed for future studies of ETV and TDF to facilitate conclusive comparisons. Patients with cirrhosis are at significantly elevated risk for HCC, despite the benefits of NA treatment.

Safety and efficacy of tenofovir alafenamide in liver transplant recipients: A single center experience

BACKGROUND

Tenofovir disoproxil fumarate (TDF) is frequently used for treatment of and prophylaxis against reactivation of hepatitis B virus (HBV) after liver transplant (LT). Because TDF can lead to renal impairment and a decrease in bone mineral density (BMD), the prodrug tenofovir alafenamide (TAF) may be considered a viable alternative with fewer adverse effects. Only limited information is available about the use of TAF for LT recipients. We report a European single-center experience with TAF as treatment for LT patients.

METHODS

This retrospective analysis involved 29 LT recipients receiving standard immunosuppressants (mainly calcineurin inhibitors). Demographic and clinical data were documented at baseline upon switch to TAF and at various time points thereafter.

RESULTS

None of the patients experienced HBV reactivation after the switch to TAF. Liver and renal function remained stable. Drug levels of immunosuppressive agents did not change significantly after the switch. After 1 year, 22 patients were still taking TAF; two patients had been lost to follow-up; one patient had died; and four patients had discontinued therapy because of TAF-related adverse effects. No serious adverse effects were reported.

CONCLUSIONS

Tenofovir alafenamide exhibits high antiviral efficacy and a good safety profile for LT recipients. Still, the safety and tolerability of TAF for organ transplant patients should be evaluated in larger cohorts.

Co-crystals, Salts or Mixtures of Both? The Case of Tenofovir Alafenamide Fumarates

Tenofovir alafenamide fumarate (TAF) is the newest prodrug of tenofovir that constitutes several drug products used for the treatment of HIV/AIDS. Although the solid-state properties of its predecessor tenofovir disoproxil fumarate have been investigated and described in the literature, there are no data in the scientific literature on the solid state properties of TAF. In our report, we describe the preparation of two novel polymorphs II and III of tenofovir alafenamide monofumarate (TA MF2 and TA MF3). The solid-state structure of these compounds was investigated in parallel to the previously known tenofovir alafenamide monofumarate form I (TA MF1) and tenofovir alafenamide hemifumarate (TA HF). Interestingly, the single-crystal X-ray diffraction of TA HF revealed that this derivative exists as a co-crystal form. In addition, we prepared a crystalline tenofovir alafenamide free base (TA) and its hydrochloride salt (TA HCl), which enabled us to determine the structure of TA MF derivatives using ¹⁵N-ssNMR (¹⁵N-solid state nuclear magnetic resonance). Surprisingly, we observed that TA MF1 exists as a mixed ionization state complex or pure salt, while TA MF2 and TA MF3 can be obtained as pure co-crystal forms.

Current practice and contrasting views on discontinuation of nucleos(t)ide analog therapy in chronic hepatitis B

Introduction: Long-term, even indefinite treatment with nucleos(t)ide analogs (NAs) is the current first-line therapy for patients with chronic hepatitis B (CHB), regardless of its histological stage. Guidelines and recommendations on duration and endpoints of NA therapy in CHB are not identical and change over time.Areas covered: The authors review NA discontinuation approaches and views with an emphasis on HBeAg-negative patients based on published studies relevant to the topic, stressing on whether or not the optimal endpoint of HBsAg loss is practically achievable.Expert opinion: Discontinuation of NA therapy in HBeAg-negative noncirrhotic patients has to be considered after long-term effective treatment with controlled liver disease activity, undetectable viremia, and significant decline in serum HBsAg titers. Close post-treatment monitoring is required for early intervention in cases of severe clinical relapse. Immediate retreatment hampers the favorable outcome of HBsAg clearance (functional cure) and should be avoided in transient ALT flares. Predictors of such relapses are still under investigation and include viral and patient factors. For HBeAg-positive noncirrhotic patients, there is wide acceptance of the endpoint of HBeAg seroconversion, after a long consolidation period.

Structural features in common of HBV and HIV-1 resistance against chirally-distinct nucleoside analogues entecavir and lamivudine

Chronic hepatitis B virus (HBV) infection is a major public health problem that affects millions of people worldwide. Nucleoside analogue reverse transcriptase (RT) inhibitors, such as entecavir (ETV) and lamivudine (3TC), serve as crucial anti-HBV drugs. However, structural studies of HBV RT have been hampered due to its unexpectedly poor solubility. Here, we show that human immunodeficiency virus type-1 (HIV-1) with HBV-associated amino acid substitutions Y115F/F116Y/Q151M in its RT (HIV^{Y115F/F116Y/Q151M}) is highly susceptible to ETV and 3TC. Additionally, we experimentally simulated previously reported ETV/3TC resistance for HBV using HIV^{Y115F/F116Y/Q151M} with F160M/M184V (L180M/M204V in HBV RT) substituted. We determined crystal structures for HIV-1 RT^{Y115F/F116Y/Q151M}:DNA complexed with 3TC-triphosphate (3TC-TP)/ETV-triphosphate (ETV-TP)/dCTP/dGTP. These structures revealed an atypically tight binding conformation of 3TC-TP, where the Met184 side-chain is pushed away by the oxathiolane of 3TC-TP and exocyclic methylene of ETV-TP. Structural analysis of RT^{Y115F/F116Y/Q151M/F160M/M184V}:DNA:3TC-TP also demonstrated that the loosely bound 3TC-TP is misaligned at the active site to prevent a steric clash with the side chain γ-methyl of Val184. These findings shed light on the common structural mechanism of HBV and HIV-1 resistance to 3TC and ETV and should aid in the design of new agents to overcome drug resistance to 3TC and ETV.

A label-free immunosensor for the sensitive detection of hepatitis B e antigen based on PdCu tripod functionalized porous graphene nanoenzymes

Nanomaterials with enzyme properties possess excellent catalytic activity and stability. We prepared new nanoenzymes to construct a label-free electrochemical immunosensor for the detection of hepatitis B e antigen (HBe Ag). In this study, PdCu tripod (PdCu TP) functionalized porous graphene (PG) nanoenzymes (PdCu TPs/PG) were prepared through the in situ reduction of PdCu tripods onto porous graphene. The catalytic Michaelis-Menten kinetic parameters of PdCu TPs/PG are better than horseradish peroxidase (HRP) and show enhanced peroxidase-like activity. Therefore, we used PdCu TPs/PG to catalyse the electrochemically active matrix of H₂O₂ and generate the synergistically amplified current signal for the subsequent sensitive detection of HBe Ag. Due to the good conductivity, large specific surface area and synergistic amplification of PdCu TPs/PG, the quantitative detection of HBe Ag shows a detection limit of 20 fg·mL^-1 and linear range from 60 fg·mL^-1 to 100 ng·mL^-1. During the detection of human serum samples, PdCu TPs/PG shows good accuracy based on the standard addition method and a comparison with an ELISA. The prepared immunosensors exhibiting good selectivity, stability and reproducibility provide an important basis for determining the prognosis of hepatitis B and show potential applications in medical applications.

Hepatitis B Virus Reactivation: Risk Factors and Current Management Strategies

Hepatitis B virus (HBV) is a global disease with significant morbidity and mortality. Worldwide, ~257 million people are chronically infected with HBV, defined as having a positive hepatitis B surface antigen, but millions more have prior HBV exposure indicated by positive hepatitis B core antibody. Reactivation of hepatitis B implies a sudden increase in viral replication in a patient with chronic HBV infection or prior HBV exposure. Hepatitis B virus reactivation (HBVr) can occur spontaneously, but it is more commonly triggered by immunosuppressive therapies for cancer, immunologic diseases, or transplantation. Elimination of hepatitis C virus (HCV) in HBV-HCV coinfected individuals treated with direct-acting antivirals (DAAs) has also been identified as an important cause of HBVr. Hepatitis B virus reactivation is an underappreciated but important complication of common medical therapies that can delay treatment or result in clinical episodes of hepatitis, hepatic failure, or death. In this review, factors associated with HBVr, particularly medication-related risks, are explored. We review data involving rituximab and ofatumumab, doxorubicin, corticosteroids, tumor necrosis factor antagonists, tyrosine kinases, bortezomib, hematologic stem cell transplantation, and DAAs for HCV treatment. In addition, we discuss screening strategies, choice of antiviral prophylaxis, and the optimal duration of therapy for HBVr. With additional awareness, screening, and appropriate antiviral therapy, it is expected that most cases of HBVr can be prevented.

Synthesis of fluorinated acyclic nucleoside phosphonates with 5-azacytosine base moiety

With respect to the strong antiviral activity of (S)-1-[3-hydroxy-2-(phosphonomethoxy)propyl]-5-azacytosine various types of its side chain fluorinated analogues were prepared. The title compound, (S)-1-[3-fluoro-2-(phosphonomethoxy)propyl]-5-azacytosine (FPMP-5-azaC) was synthesised by the condensation reaction of (S)-2-[(diisopropoxyphosphoryl)methoxy)-3-fluoropropyl p-toluenesulfonate with a sodium salt of 5-azacytosine followed by separation of appropriate N¹ and O² regioisomers and ester hydrolysis. Transformations of FPMP-5-azaC to its 5,6-dihydro-5-azacytosine counterpart, amino acid phosphoramidate prodrugs and systems with an annelated five-membered imidazole ring, i.e. imidazo [1,2-a][1,3,5]triazine derivatives were also carried out. 1-(2-Phosphonomethoxy-3,3,3-trifluoropropyl)-5-azacytosine was prepared from 5-azacytosine and trifluoromethyloxirane to form 1-(3,3,3-trifluoro-2-hydroxypropyl)-5-azacytosine which was treated with diisopropyl bromomethanephosphonate followed by deprotection of esters. Antiviral activity of all newly prepared compounds was studied. FPMP-5-azaC diisopropyl ester inhibited the replication of herpes viruses with EC₅₀ values that were about three times higher than that of the reference anti-HCMV drug ganciclovir without displaying cytotoxicity.

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5-Azacytosine acyclic nucleoside phosphonates fluorinated in the aliphatic side chain have been synthesized.

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Stabilized analogues with 5,6-dihydro arrangement and/or with an annelated five-membered ring were also prepared.

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Diisopropyl phosphonate esters were converted to amino acid amidate prodrugs.

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In most cases, antiviral activity of the compounds was only marginal.

Switching from entecavir to tenofovir alafenamide versus maintaining entecavir for chronic hepatitis B

Tenofovir alafenamide (TAF) is a newly developed prodrug of tenofovir (TFV). We divided 48 chronic hepatitis B patients who had taken entecavir (ETV) for ≥2 years into two groups: the ETV continuation (n = 24) and the TAF switching (n = 24) groups, and compared the antiviral effects and safety until 48 weeks after the start of the study. There were no significant differences in the alterations in the serum levels of HBs antigen (HBsAg) level between the ETV continuation and the TAF switching groups at 24 or 48 weeks. We also examined the effect of baseline HBsAg level on the decrease of HBsAg during the treatment; in the TAF switching group, the decrease of HBsAg level at 48 weeks was more significant in patients with low baseline HBsAg (<800 IU/mL) than those with high baseline HBsAg ( >800 IU/mL) (change of HBsAg; - 0.029 vs - 0.132 for high and low baseline HBsAg, respectively, P = .007). Also, the effect on renal function was found to be comparable between the TAF switch group and the ETV continuation group. In this study, switching from ETV to TAF may represent higher efficacy for a decrease of HBsAg than a continuation of ETV among the patients with low baseline HBsAg level.

Patient-Reported Symptoms Over 48 Weeks Among Participants in Randomized, Double-Blind, Phase III Non-inferiority Trials of Adults with HIV on Co-formulated Bictegravir, Emtricitabine, and Tenofovir Alafenamide versus Co-formulated Abacavir, Dolutegravir, and Lamivudine

Background

Integrase strand transfer inhibitors (INSTIs) are recommended for first-line antiretroviral therapy in combination with two nucleos(t)ide reverse transcriptase inhibitors. Co-formulated bictegravir, emtricitabine, and tenofovir alafenamide (B/F/TAF), a novel, INSTI-based regimen, is currently approved in the US and EU for the treatment of HIV-1 infection and recommended as first-line treatment in current guidelines. In our current analysis, we aimed to determine changes in patient-reported symptoms over time among HIV-1-infected adults who initiated or switched to B/F/TAF versus another INSTI-based regimen, co-formulated abacavir, dolutegravir, and lamivudine (ABC/DTG/3TC).

Methods

A planned secondary analysis of patient-reported outcomes was conducted for two double-blind, randomized, phase III studies in HIV-1-infected adults comparing B/F/TAF with ABC/DTG/3TC: one in treatment-naïve individuals (GS-US-380-1489, ClinicalTrials.gov NCT02607930) and the other in virologically suppressed participants (GS-US-380-1844, ClinicalTrials.gov NCT02603120). In both studies, the HIV symptoms distress module (HIV-SI) was administered at baseline (BL) and weeks 4, 12, and 48. Responses to each of the 20 items were dichotomized as bothersome or not bothersome. Treatment differences were assessed using unadjusted and adjusted logistic regression models (adjusted for BL HIV-SI count, age, sex, BL Veterans Aging Cohort Study [VACS] Index, medical history of serious mental illness, BL Short Form [SF]-36 Physical Component Summary [PCS], BL SF-36 Mental Component Summary [MCS], and, for virologically suppressed participants only, years since HIV diagnosis). We conducted longitudinal modeling of bothersome symptoms using a generalized mixed model including treatment, time, time-by-treatment, and additional covariates from the adjusted logistic regression model as described above. The Pittsburgh Sleep Quality Index (PSQI) was administered at the same frequency as the HIV-SI, and the total score was dichotomized as good or poor sleep quality. Similar models to those used for HIV-SI were applied, using BL sleep quality and BL SF-36 MCS as covariates. Statistical significance was assessed using p < 0.05.

Results

Across both studies, bothersome symptoms were reported by fewer participants on B/F/TAF than those on ABC/DTG/3TC. In treatment-naïve adults, fatigue/loss of energy, nausea/vomiting, dizzy/lightheadedness, and difficulty sleeping were reported significantly less with B/F/TAF at two or more time points. Fatigue and nausea were also significantly less common for those receiving B/F/TAF in longitudinal models. In virologically suppressed participants, nausea/vomiting, sad/down/depressed, nervous/anxious, and poor sleep quality (from the PSQI) were reported significantly less with B/F/TAF at two or more time points, as well as in longitudinal models.

Conclusions

B/F/TAF was associated with lower prevalence of bothersome symptoms than ABC/DTG/3TC in both treatment-naïve and virologically suppressed adults.

Electronic supplementary material

The online version of this article (10.1007/s40271-018-0322-8) contains supplementary material, which is available to authorized users.

Unmet need in chronic hepatitis B management

Despite all these exciting developments, there remain some unmet needs in the management for patients with chronic hepatitis B (CHB). As majority of CHB patients are going to use oral nucleos(t)ide analogues (NAs) for decades, Safety profile of NAs is of no doubt an important issue. The newest nucleotide analogue tenofovir alafenamide is potent in terms of viral suppression, together with favourable renal and bone safety profile. Biochemical response as reflected by alanine aminotransferase (ALT) normalization is recently found to be prognostically important. Patients who achieved ALT normalization have reduced the risk of hepatic events by 49%. Functional cure as reflected by hepatitis B surface antigen seroclearance not only implies patients may stop NA treatment, it also confers to a reduced risk of hepatocellular carcinoma and other hepatic events. Hence functional cure should be the ultimate treatment goal in CHB patients. Preemptive antiviral treatment may reduce mother-to-child transmission of hepatitis B virus, especially if birth dose of vaccination cannot be given in the first two hours after delivery. Lastly, despite the currently first-line NAs have high-genetic barrier to drug resistance mutations, there are still are many patients who were previously treated with low barrier of resistance including lamivudine, telbivudine or adefovir dipivoxil which could lead to antiviral resistance and affecting the choice of NAs.

Switching to peginterferon for chronic hepatitis B patients with hepatitis B e antigen seroconversion on entecavir - A prospective study

Nucleos(t)ide analogues (NA) are effective in suppressing hepatitis B virus (HBV) replication, but most patients require long-term treatment. This study aimed to investigate switching to peginterferon as a strategy to stop NA. Hepatitis B e antigen (HBeAg)-positive chronic hepatitis B patients who developed HBeAg seroconversion during NA treatment were studied. All patients received open-label peginterferon alfa-2a 180 μg/wk for 48 weeks, and NA was stopped at week 4 of peginterferon treatment. The primary endpoint was sustained response, which was defined as negative HBeAg, positive anti-HBe and HBV DNA <2000 IU/mL at week 72. Other secondary endpoints including HBsAg loss at week 72 were also studied. Forty-one patients treated with entecavir for 56 ± 23 months were recruited. Sustained response was achieved in 30 patients (73%, 95% confidence interval 58%-84%). At week 72, 31 (76%) patients had HBeAg seroconversion, 56 (23%) patients had undetectable HBV DNA, 31 (76%) patients had normal ALT, and 6 patients (15%) had HBsAg loss. Baseline HBsAg level was the best predictor for both sustained response and HBsAg loss; the best HBsAg cut-off for sustained response was <1500 IU/mL and that for HBsAg loss was <500 IU/mL by receiver operating characteristic curve analysis. Twenty-two of 25 (88%) patients with baseline HBsAg <1500 IU/mL had sustained response. Five of 10 (50%) patients with baseline HBsAg <500 IU/mL developed HBsAg loss. Switching to peginterferon can be considered as a treatment option in NA-treated patients with HBeAg seroconversion, particularly among those with lower HBsAg levels.

Normal on-treatment ALT during antiviral treatment is associated with a lower risk of hepatic events in patients with chronic hepatitis B

BACKGROUND & AIMS

Recent studies reveal that the rate of normal on-treatment alanine aminotransferase (ALT) appears different for different nucleos(t)ide analogues (NAs); yet its clinical significance is unclear. We aimed to evaluate the impact of normal on-treatment ALT during antiviral treatment with entecavir (ETV) or tenofovir disoproxil fumarate (TDF) in patients with chronic hepatitis B (CHB).

METHODS

A territory-wide cohort of patients with CHB who received ETV and/or TDF in 2005-2016 was identified. Serial on-treatment ALT levels were collected and analyzed. Normal on-treatment ALT (ALT-N) was defined as ALT <30 U/L in males and <19 U/L in females. The primary and secondary outcomes were composite hepatic events (including hepatocellular carcinoma) based on diagnostic codes. Patients with hepatic events before or during the first year of antiviral treatment or follow-up <1 year were excluded.

RESULTS

A total of 21,182 patients with CHB (10,437 with and 10,745 without ALT-N at 12 months after antiviral treatment) were identified and followed for 4.0 ± 1.7 years. Patients with and without ALT-N differed in baseline ALT (58 vs. 61 U/L), hepatitis B virus DNA (4.9 vs. 5.1 log10 IU/ml) and cirrhosis status (8.8% vs. 10.5%). A total of 627 (3.0%) patients developed composite hepatic events. Compared to no ALT-N, ALT-N at 3, 6, 9 and 12 months reduced the risk of hepatic events, after adjustment for baseline ALT and other important covariates, with adjusted hazard ratios (95% CI) of 0.61 (0.49-0.77), 0.55 (0.45-0.67), 0.54 (0.44-0.65) and 0.51 (0.42-0.61) respectively (all p <0.001). The cumulative incidence (95% CI) of composite hepatic events at six years was 3.51% (3.06%-4.02%) in ALT-N and 5.70% (5.15%-6.32%) in the no ALT-N group (p <0.001).

CONCLUSIONS

Normal on-treatment ALT is associated with a lower risk of hepatic events in patients with CHB receiving NA treatment, translating into improved clinical outcomes in these patients.

LAY SUMMARY

We investigated 21,182 patients with chronic hepatitis B receiving antiviral treatment. Alanine aminotransferase is a laboratory marker of liver function, with raised levels indicating liver dysfunction and in severe cases hepatitis. Normal on-treatment alanine aminotransferase during the first year of treatment in patients with CHB is associated with a lower risk of hepatic events.

Patient-Reported Symptoms Over 48 Weeks Among Participants in Randomized, Double-Blind, Phase III Non-inferiority Trials of Adults with HIV on Co-formulated Bictegravir, Emtricitabine, and Tenofovir Alafenamide versus Co-formulated Abacavir, Dolutegravir, and Lamivudine

BACKGROUND

Integrase strand transfer inhibitors (INSTIs) are recommended for first-line antiretroviral therapy in combination with two nucleos(t)ide reverse transcriptase inhibitors. Co-formulated bictegravir, emtricitabine, and tenofovir alafenamide (B/F/TAF), a novel, INSTI-based regimen, is currently approved in the US and EU for the treatment of HIV-1 infection and recommended as first-line treatment in current guidelines. In our current analysis, we aimed to determine changes in patient-reported symptoms over time among HIV-1-infected adults who initiated or switched to B/F/TAF versus another INSTI-based regimen, co-formulated abacavir, dolutegravir, and lamivudine (ABC/DTG/3TC).

METHODS

A planned secondary analysis of patient-reported outcomes was conducted for two double-blind, randomized, phase III studies in HIV-1-infected adults comparing B/F/TAF with ABC/DTG/3TC: one in treatment-naïve individuals (GS-US-380-1489, ClinicalTrials.gov NCT02607930) and the other in virologically suppressed participants (GS-US-380-1844, ClinicalTrials.gov NCT02603120). In both studies, the HIV symptoms distress module (HIV-SI) was administered at baseline (BL) and weeks 4, 12, and 48. Responses to each of the 20 items were dichotomized as bothersome or not bothersome. Treatment differences were assessed using unadjusted and adjusted logistic regression models (adjusted for BL HIV-SI count, age, sex, BL Veterans Aging Cohort Study [VACS] Index, medical history of serious mental illness, BL Short Form [SF]-36 Physical Component Summary [PCS], BL SF-36 Mental Component Summary [MCS], and, for virologically suppressed participants only, years since HIV diagnosis). We conducted longitudinal modeling of bothersome symptoms using a generalized mixed model including treatment, time, time-by-treatment, and additional covariates from the adjusted logistic regression model as described above. The Pittsburgh Sleep Quality Index (PSQI) was administered at the same frequency as the HIV-SI, and the total score was dichotomized as good or poor sleep quality. Similar models to those used for HIV-SI were applied, using BL sleep quality and BL SF-36 MCS as covariates. Statistical significance was assessed using p < 0.05.

RESULTS

Across both studies, bothersome symptoms were reported by fewer participants on B/F/TAF than those on ABC/DTG/3TC. In treatment-naïve adults, fatigue/loss of energy, nausea/vomiting, dizzy/lightheadedness, and difficulty sleeping were reported significantly less with B/F/TAF at two or more time points. Fatigue and nausea were also significantly less common for those receiving B/F/TAF in longitudinal models. In virologically suppressed participants, nausea/vomiting, sad/down/depressed, nervous/anxious, and poor sleep quality (from the PSQI) were reported significantly less with B/F/TAF at two or more time points, as well as in longitudinal models.

CONCLUSIONS

B/F/TAF was associated with lower prevalence of bothersome symptoms than ABC/DTG/3TC in both treatment-naïve and virologically suppressed adults.

Current evidence on the management of hepatitis B in pregnancy

Hepatitis B virus (HBV) infection is one of the main public health problems across the globe, since almost one third of the world population presents serological markers of contact with the virus. A profound impact on the epidemiology has been exerted by universal vaccination programmes in many countries, nevertheless the infection is still widespread also in its active form. In the areas of high endemicity (prevalence of hepatitis B surface antigen positivity > 7%), mother-to-child transmission represents the main modality of infection spread. That makes the correct management of HBV in pregnancy a matter of utmost importance. Furthermore, the infection in pregnancy needs to be carefully assessed and handled not only with respect to the risk of vertical transmission but also with respect to gravid women health. Each therapeutic or preventive choice deserves to be weighed upon attentively. On many aspects evidence is scarce or controversial. This review will highlight the latest insights into the paramount steps in managing HBV in pregnancy, with particular attention to recommendations from recent guidelines and data from up-do-date research syntheses.

Discovery of the Novel Entecavir-Resistant Hepatitis B Virus Reverse Transcriptase A181C Substitution From an Integrated Genotypic Analysis

Entecavir (ETV) is a first-line therapy for chronic hepatitis B virus (HBV), demonstrating potent suppression of HBV DNA and a high barrier to viral resistance. Previous studies revealed that ETV-resistant (ETVr) HBV DNA resulted from substitutions in the HBV reverse transcriptase (RT) at positions rtT184, rtS202, or rtM250 in combination with lamivudine resistance (LVDr) substitutions rtM204I/V±rtL180M. In vitro, viral variants exhibit varying degrees of ETV susceptibility and replication capacity depending on specific resistance substitutions. To explore the potential for additional pathways to ETVr, HBV RT sequences from 982 evaluable patients enrolled in 17 ETV clinical studies were analyzed. Thirty novel emergent substitutions at amino acid positions not previously associated with HBV nucleos(t)ide drug resistance were observed in at least 2 patients and were identified in patient-derived HBV with a wild-type, LVDr, or ETVr RT sequence. Phenotypic analysis of these substitutions indicated that they had no effect on ETV susceptibility. Phenotypic analysis was also performed on patient-derived HBV RT sequences from 10 LVD-naive and 13 LVD-experienced patients with virologic breakthrough and emergent novel substitutions while on ETV treatment. One LVD-experienced patient-derived HBV RT harboring LVDr substitutions rtL180M+rtM204V with rtA181C displayed reduced ETV susceptibility (122-fold greater than wild-type HBV) and remained susceptible to adefovir and tenofovir. HBV harboring the rtA181C substitution without LVDr substitutions rtL180M+rtM204V remained susceptible to inhibition by ETV, adefovir, and tenofovir, although cross-resistance to LVD and telbivudine was observed. Conclusion: An integrated genotypic analysis of HBV RT sequences from patients with chronic HBV treated with ETV led to the discovery of the novel ETVr substitution rtA181C. This substitution was always detected in combination with LVDr substitutions rtL180M+rtM204V in ETV-treated patients.

Expedient synthesis and biological evaluation of alkenyl acyclic nucleoside phosphonate prodrugs

The importance of phosphonoamidate prodrugs (ProTides) of acyclic nucleoside phosphonate (ANPs) is highlighted by the approval of Tenofovir Alafenamide Fumarate for the treatment of HIV and HBV infections. In the present paper we are reporting an expedient, one-pot, two-steps synthesis of allyl phosphonoamidates and diamidates that offers a time saving strategy when compared to literature methods. The use of these substrates in the cross metathesis reactions with alkenyl functionalised thymine and uracil nucleobases is reported. ANPs prodrugs synthesized via this methodology were evaluated for their antiviral activities against DNA and RNA viruses. It is anticipated that the use of 5,6,7,8-tetrahydro-1-napthyl as aryloxy moiety is capable to confer antiviral activity among a series of otherwise inactive uracil ProTides.

Switching to fixed-dose bictegravir, emtricitabine, and tenofovir alafenamide from dolutegravir plus abacavir and lamivudine in virologically suppressed adults with HIV-1: 48 week results of a randomised, double-blind, multicentre, active-controlled, phase 3, non-inferiority trial

BACKGROUND

Bictegravir, co-formulated with emtricitabine and tenofovir alafenamide, has shown good efficacy and tolerability, and similar bone, renal, and lipid profiles to dolutegravir, abacavir, and lamivudine, in treatment-naive adults with HIV-1 infection, without development of treatment-emergent resistance. Here, we report 48-week results of a phase 3 study investigating switching to bictegravir, emtricitabine, and tenofovir alafenamide from dolutegravir, abacavir, and lamivudine in virologically suppressed adults with HIV-1 infection.

METHODS

In this multicentre, randomised, double-blind, active-controlled, non-inferiority, phase 3 trial, HIV-1-infected adults were enrolled at 96 outpatient centres in nine countries. Eligible participants were aged 18 years or older and on a regimen of 50 mg dolutegravir, 600 mg abacavir, and 300 mg lamivudine (fixed-dose combination or multi-tablet regimen); had an estimated glomerular filtration rate of 50 mL/min or higher; and had been virologically suppressed (plasma HIV-1 RNA <50 copies per mL) for 3 months or more before screening. We randomly assigned participants (1:1), using a computer-generated randomisation sequence, to switch to co-formulated bictegravir (50 mg), emtricitabine (200 mg), and tenofovir alafenamide (25 mg; herein known as the bictegravir group), or to remain on dolutegravir, abacavir, and lamivudine (herein known as the dolutegravir group), once daily for 48 weeks. The investigators, participants, study staff, and individuals assessing outcomes were masked to treatment assignment. The primary endpoint was the proportion of participants with plasma HIV-1 RNA of 50 copies per mL or higher at week 48 (according to the US Food and Drug Administration snapshot algorithm); the prespecified non-inferiority margin was 4%. The primary efficacy and safety analyses included all participants who received at least one dose of study drug. This study is ongoing but not actively recruiting participants and is in the open-label extension phase, wherein participants are given the option to receive bictegravir, emtricitabine, and tenofovir alafenamide for an additional 96 weeks. This trial is registered with ClinicalTrials.gov, number NCT02603120.

FINDINGS

Between Nov 11, 2015, and July 6, 2016, 567 participants were randomly assigned and 563 were treated (282 received bictegravir, emtricitabine, and tenofovir alafenamide, and 281 received dolutegravir, abacavir, and lamivudine). Switching to the bictegravir regimen was non-inferior to remaining on dolutegravir, abacavir, and lamivudine for the primary outcome: three (1%) of 282 in the bictegravir group had HIV-1 RNA of 50 copies per mL or higher at week 48 versus one (<1%) of 281 participants in the dolutegravir group (difference 0·7%, 95·002% CI -1·0 to 2·8; p=0·62). Treatment-related adverse events were recorded in 23 (8%) participants in the bictegravir group and 44 (16%) in the dolutegravir group. Treatment was discontinued because of adverse events in six (2%) participants in the bictegravir group and in two (1%) participants in the dolutegravir group.

INTERPRETATION

The fixed-dose combination of bictegravir, emtricitabine, and tenofovir alafenamide might provide a safe and efficacious option for ongoing treatment of HIV-1 infection.

FUNDING

Gilead Sciences.

Synthesis and antiviral evaluation of cyclopentyl nucleoside phosphonates

The synthesis of both 2'-hydroxy-3'-deoxy and 2'-deoxy-3'-hydroxy cyclopentyl nucleoside phosphonates with the natural nucleobases adenine, thymine, cytosine and guanine from a single precursor has been performed. The guanine containing analogues showed antiviral activity. Especially the 3'-deoxy congener 23 was active, displaying an EC₅₀ of 5.35 μM against TK⁺ VZV strain and an EC₅₀ of 8.83 μM against TK^- VZV strain, besides lacking cytotoxicity. However, the application of phosphonodiamidate prodrug strategy did not lead to a boost in antiviral activity.

INASL Position Statements on Prevention, Diagnosis and Management of Hepatitis B Virus Infection in India: The Andaman Statements

Hepatitis B Virus (HBV) infection is one of the major causes of morbidity, mortality and healthcare expenditure in India. There are no Indian consensus guidelines on prevention, diagnosis and management of HBV infection. The Indian National Association for Study of the Liver (INASL) set up a taskforce on HBV in 2016, with a mandate to develop consensus guidelines for diagnosis and management of HBV infection, relevant to disease patterns and clinical practices in India. The taskforce first identified contentious issues on various aspects of HBV management, which were allotted to individual members of the taskforce who reviewed them in detail. A 2-day round table discussion was held on 11th and 12th February 2017 at Port Blair, Andaman & Nicobar Islands, to discuss, debate, and finalize the consensus statements. The members of the taskforce reviewed and discussed the existing literature threadbare at this meeting and formulated the 'INASL position statements' on each of the issues. The evidence and recommendations in these guidelines have been graded according to the Grading of Recommendations Assessment Development and Evaluation (GRADE) system with minor modifications. The strength of recommendations (strong: 1, weak: 2) thus reflects the quality (grade) of underlying evidence (A, B, C, D). We present here the INASL position statements on prevention, diagnosis and management of HBV in India.

Role of tenofovir alafenamide (TAF) in the treatment and prophylaxis of HIV and HBV infections

Tenofovir (TFV) is the cornerstone of the treatment and prophylaxis of HIV infections. It has been routinely used in its prodrug form TDF (tenofovir disoproxil fumarate) combined with emtricitabine ((-)FTC) and other antiretroviral agents. TDF has now been replaced by TAF (tenofovir alafenamide) which allows better uptake by the lymphoid tissue. In combination with elvitegravir (E), cobicistat (C), emtricitabine (F), TAF can be advocated as an STR (single tablet regimen, Genvoya®) for the treatment of HIV infections. In this combination, E and C may in the future be replaced by bictegravir. The prophylaxis of HIV infection is momentarily based upon Truvada®, the combination of F with TDF, which in the future may also be replaced by TAF. TAF (Vemlidy®) has also replaced TDF (Viread®) for the treatment of hepatitis B virus (HBV) infections. Both TDF and TAF offer little or no risk for virus-drug resistance. As compared to TDF, TAF limits the risk for nephrotoxicity and loss of bone mineral density. What remains to be settled, however, before the universal use of TAF could be recommended, is its safety during pregnancy and its applicability in the treatment of tuberculosis, in combination with rifampicin.