Efficacy and safety of tenofovir disoproxil fumarate in patients with chronic hepatitis B

Degradants of Tenofovir Disoproxil Fumarate Under Forced Yet Mild Thermal Stress: Isolation, Comprehensive Structural Elucidation, and Mechanism

In addition to understanding the mechanism of action for a specific drug candidate, information regarding degradation pathways/products under various stress conditions is essential to know about their short- and long-term effects on health and environment. In line with that, tenofovir disoproxil fumarate (TDF, a co-crystal form of the prodrug tenofovir with fumaric acid), particularly used as an antiretroviral drug for treatment of HIV and hepatitis-B among others, is subjected to primarily thermal and other ICH-prescribed forced degradation conditions and their various degradation products are identified. Upon thermal degradation at 60°C for 8 h, five different degradants (namely DP-1 to DP-5) are isolated, and their structures are unambiguously confirmed using advanced analytical and spectroscopic techniques including ultra-performance liquid chromatography-mass spectrometry (UPLC-MS), high-resolution mass spectrometry (HRMS), state-of-the-art 1- and 2-dimensional nuclear magnetic resonance (1D and 2D NMR), and Fourier-transform infrared spectroscopic (FT-IR) techniques. Among fully characterized five degradants, two new degradants (DP-2 and DP-4) are identified which can potentially impact the stability of TDF via different pathways. Plausible mechanisms leading to all five thermal degradation products are also proposed including the generation of carcinogenic formaldehyde for some cases. The present systematic structural study especially combining MS and advanced NMR investigations unequivocally confirms the structures of the degradants and opens opportunities for connecting the various degradation pathways especially for the TDF-related pharmaceutical candidates.

HIV-HBV Coinfection-Current Challenges for Virologic Monitoring

HIV-HBV coinfected patients have higher rates of liver-related morbidity, hospitalizations, and mortality compared to HBV or HIV mono-infected ones. Clinical studies have shown an accelerated progression of liver fibrosis and an increased incidence of HCC, resulting from the combined action of HBV replication, immune-mediated hepatocytolysis, and HIV-induced immunosuppression and immunosenescence. Antiviral therapy based on dually active antiretrovirals is highly efficient, but late initiation, global disparities in accessibility, suboptimal regimens, and adherence issues may limit its impact on the development of end-stage liver disease. In this paper, we review the mechanisms of liver injuries in HIV-HBV coinfected patients and the novel biomarkers that can be used for treatment monitoring in HIV-HBV coinfected persons: markers that assess viral suppression, markers for liver fibrosis evaluation, and predictors of oncogenesis.

Significant perspectives on various viral infections targeted antiviral drugs and vaccines including COVID-19 pandemicity

A virus enters a living organism and recruits host metabolism to reproduce its own genome and proteins. The viral infections are intricate and cannot be completely removed through existing antiviral drugs. For example, the herpes, influenza, hepatitis and human immunodeficiency viruses are a few dreadful ones amongst them. Significant studies are needed to understand the viral entry and their growth in host cells to design effective antivirals. This review emphasizes the range of therapeutical antiviral drugs, inhibitors along with vaccines to fight against viral pathogens, especially for combating COVID-19. Moreover, we have provided the basic and in depth information about viral targets, drugs availability, their mechanisms of action, method of prevention of viral diseases and highlighted the significances of anticoagulants, convalescent plasma for COVID-19 treatment, scientific details of airborne transmission, characteristics of antiviral drug delivery using nanoparticles/carriers, nanoemulsions, nanogels, metal based nanoparticles, alike the future nanosystems through nanobubbles, nanofibers, nanodiamonds, nanotraps, nanorobots and eventually, the therapeutic applications of micro- and nanoparticulates, current status for clinical development against COVID-19 together with environmental implications of antivirals, gene therapy etc., which may be useful for repurposing and designing of novel antiviral drugs against various dreadful diseases, especially the SARS-CoV-2 and other associated variants.

Hepatitis B Core-Related Antigen Is Useful for Predicting Phase and Prognosis of Hepatitis B e Antigen-Positive Patients

The role of hepatitis B core-related antigen (HBcrAg) level in defining clinical phase and predicting prognosis of chronic hepatitis B (CHB) has not been fully studied. CHB patients who had undergone liver biopsy in Korea University Medical Center were included. Patients with liver cirrhosis were excluded. The associations of HBcrAg level with CHB phase, and nucleos(t)ide analogue (NA)-induced hepatitis B e antigen (HBeAg) seroconversion were analyzed. In total, 387 patients (median follow-up of 82.4 months) were included. The CHB phases of patients were defined histologically as immune-tolerant (IT, n = 32, 8.3%), HBeAg-positive and immune-active (PIA, n = 211, 54.5%), HBeAg-negative and immune-active (n = 125, 32.3%), and inactive (n = 19, 4.9%), respectively. In HBeAg-positive patients, the mean HBV DNA levels were comparable between the two groups (p = 0.990). However, the mean HBsAg (7.4 log IU/mL and 6.9 log IU/mL, p = 0.002) and HBcrAg levels (8.2 log U/mL vs. 7.6 log U/mL, p < 0.001) of IT patients were significantly higher than that of PIA patients. In multivariate analysis, younger age (odds ratio [OR] 0.949, p = 0.025), lower alanine aminotransferase (OR 0.988, p = 0.002) and higher HBcrAg level (OR = 2.745 p = 0.022) were independent predictors of the IT phase. Of the patients in the PIA phase, 194 received NA after liver biopsy, and 61 (31.4%) had achieved HBeAg seroconversion after antiviral therapy. In Cox regression analysis, the higher HBcrAg level was the only independent predictor of the NA-induced HBeAg seroconversion (hazard ratio 1.285, p = 0.028). The HBcrAg level is useful for predicting clinical phase of CHB and NA-induced HBeAg seroconversion in HBeAg-positive patients.

Non-Inferior Efficacy of Tenofovir Disoproxil to Tenofovir Disoproxil Fumarate in Virologically Suppressed Chronic Hepatitis B Patients

PURPOSE

Tenofovir disoproxil (TD), modified from tenofovir disoproxil fumarate (TDF), was developed as a salt-free formulation, removing fumarate to improve the ease of oral intake by reducing the tablet's size. We evaluated the maintenance of antiviral effects and overall safety profile of TD 245 mg after switching from TDF 300 mg in patients with chronic hepatitis B (CHB).

PATIENTS AND METHODS

CHB patients with HBV-DNA <69 IU/mL after ≥24 weeks of TDF therapy were enrolled. The primary efficacy endpoint was the HBV-DNA suppression rate (HBV-DNA <69 IU/mL) at week 48; We evaluated the non-inferiority (10% margin) of TD to TDF in terms of efficacy. Safety was assessed based on adverse events (AEs), laboratory tests, bone mineral density, and renal function abnormalities.

RESULTS

Overall, 189 subjects were randomized in a 2:1 ratio, and 117 and 66 subjects in the TD and TDF groups, respectively, completed the study. In the per-protocol set, the HBV-DNA suppression rate at week 48 was 99.1% and 100% in the TD and TDF groups, respectively. The lower limit of the 97.5% one-sided confidence interval for the intergroup difference in HBV-DNA suppression rate was -2.8%, which was greater than the prespecified margin of non-inferiority. The changes in creatinine clearance from baseline to week 48 was significantly less in the TD group and in the TDF group; -0.8 ± 9.8 versus -2.4 ± 12.8 mL/min, respectively (P=0.017).

CONCLUSION

TD was non-inferior to TDF for maintaining viral suppression in CHB patients, showing the less decline of renal function.

Overview of Biologically Active Nucleoside Phosphonates

The use of the phosphonate motif featuring a carbon-phosphorous bond as bioisosteric replacement of the labile P–O bond is widely recognized as an attractive structural concept in different areas of medicinal chemistry, since it addresses the very fundamental principles of enzymatic stability and minimized metabolic activation. This review discusses the most influential successes in drug design with special emphasis on nucleoside phosphonates and their prodrugs as antiviral and cancer treatment agents. A description of structurally related analogs able to interfere with the transmission of other infectious diseases caused by pathogens like bacteria and parasites will then follow. Finally, molecules acting as agonists/antagonists of P2X and P2Y receptors along with nucleotidase inhibitors will also be covered. This review aims to guide readers through the fundamentals of nucleoside phosphonate therapeutics in order to inspire the future design of molecules to target infections that are refractory to currently available therapeutic options.

Discontinuation of nucleos(t)ide analogues is not associated with a higher risk of HBsAg seroreversion after antiviral-induced HBsAg seroclearance: a nationwide multicentre study

OBJECTIVE

Direct comparison of the clinical outcomes between nucleos(t)ide analogue (NA) discontinuation versus NA continuation has not been performed in patients with chronic hepatitis B who achieved HBsAg-seroclearance. Whether NA discontinuation was as safe as NA continuation after NA-induced surface antigen of HBV (HBsAg) seroclearance was investigated in the present study.

DESIGNS

This multicentre study included 276 patients from 16 hospitals in Korea who achieved NA-induced HBsAg seroclearance: 131 (47.5%) discontinued NA treatment within 6 months after HBsAg seroclearance (NA discontinuation group) and 145 (52.5%) continued NA treatment (NA continuation group). Primary endpoint was HBsAg reversion and secondary endpoints included serum HBV DNA redetection and development of hepatocellular carcinoma (HCC).

RESULTS

During follow-up (median=26.9 months, IQR=12.2-49.2 months), 10 patients (3.6%) experienced HBsAg reversion, 6 (2.2%) showed HBV DNA redetection and 8 (2.9%) developed HCC. Compared with NA continuation, NA discontinuation was not associated with HBsAg reversion in both univariable (HR=0.45, 95% CI=0.12 to 1.76, log-rank p=0.24) and multivariable analyses (adjusted HR=0.65, 95% CI=0.16 to 2.59, p=0.54). The cumulative probabilities of HBsAg reversion at 1, 3 and 5 years were 0.8%, 2.3% and 5.0% in the NA discontinuation group, and 1.5%, 6.3% and 8.4% in the NA continuation group, respectively. NA discontinuation was not associated with higher risk of either HBV redetection (HR=0.83, 95% CI=0.16 to 4.16, log-rank p=0.82) or HCC development (HR=0.53, 95% CI=0.12 to 2.23, log-rank p=0.38).

CONCLUSION

The discontinuation of NA was not associated with a higher risk of either HBsAg reversion, serum HBV DNA redetection or HCC development compared with NA continuation among patients who achieved HBsAg seroclearance with NA.

Comparison of clinical practice guidelines for the management of chronic hepatitis B: When to start, when to change, and when to stop

Clinical practice guidelines are important for guiding the management of specific diseases by medical practitioners, trainees, and nurses. In some cases, the guidelines are utilized as a reference for health policymakers in controlling diseases with a large public impact. With this in mind, practice guidelines for the management of chronic hepatitis B (CHB) have been developed in the United States, Europe, and Asian-Pacific regions to suggest the best-fit recommendations for each social and medical circumstance. Recently, the Korean Association for the Study of the Liver published a revised version of its clinical practice guidelines for the management of CHB. The guidelines included updated information based on newly available antiviral agents, the most recent opinion on the initiation and cessation of treatment, and updates for the management of drug resistance, partial virological response, and side effects. Additionally, CHB management in specific situations was comprehensively revised. This review compares the similarities and differences among the various practice guidelines to identify unmet needs and improve future recommendations.

Extremely low risk of hepatocellular carcinoma development in patients with chronic hepatitis B in immune-tolerant phase

BACKGROUND

Anti-viral therapy is not indicated for patients with chronic hepatitis B (CHB) in the immune-tolerant phase.

AIMS

To investigate the cumulative incidence of phase change and hepatocellular carcinoma (HCC) and independent predictors for phase change in patients with CHB in immune-tolerant phase.

METHODS

In total, 946 patients in immune-tolerant phase, defined as hepatitis B e antigen positivity, HBV-DNA >20 000 IU/mL and alanine aminotransferase (ALT) ≤40 IU/L, between 1989 and 2017 were enrolled from eight institutes.

RESULTS

The mean age of study population (429 men and 517 women) was 36.7 years. The mean ALT and HBV-DNA levels were 24.6 IU/L and 8.50 log₁₀ IU/mL, respectively. Of the study population, 476 (50.3%) patients remained in immune-tolerant phase throughout the study period (median: 63.6 months). The cumulative incidence rates of phase change and HCC at 10 years were 70.7% and 1.7%, respectively. Multivariate analyses revealed that HBV-DNA level >10⁷  IU/mL was associated independently with a reduced risk of phase change (hazard ratio [HR] = 0.734, P = 0.008), whereas a high ALT level, above the cut-off recommended in the Korean Association for the Study of the Liver guidelines (34 IU/L for men and 30 IU/L for women), was associated independently with a greater risk of phase change (HR = 1.885, P < 0.001).

CONCLUSIONS

The criterion of HBV-DNA level > 10⁷  IU/mL may be useful to define immune-tolerant phase. In addition, an extremely low risk of HCC development was observed in patients with CHB in immune-tolerant phase.

Risk factors associated with hypophosphatemia in chronic Hepatitis B patients treated with tenofovir disoproxil fumarate

Tenofovir disoproxil fumarate (TDF) is thought to cause varying degrees of hypophosphatemia in patients with chronic hepatitis B (CHB). Therefore, we investigated factors that cause hypophosphatemia in patients treated with TDF and methods to increase serum phosphorus concentrations in clinical practice.We completed a retrospective review of patients with CHB treated with TDF initially at Kosin University Gospel Hospital, Busan, Korea from January 2012 to January 2017. Subclinical hypophosphatemia and hypophosphatemia were defined as serum phosphorus below 3.0 mg/dL and 2.5 mg/dL, respectively.We screened 206 patients with CHB treated with TDF, among which 135 were excluded for the following reasons: baseline malignancy (59), limited data (50), co-administered other antivirals (14), hypophosphatemia at baseline (7), and other reasons (5). The final study population comprised 71 patients. Subclinical hypophosphatemia developed in 43 (60.5%) patients. Hypophosphatemia occurred in 18 patients (25.3%). Liver cirrhosis was the most significant predictor of hypophosphatemia (P = .038, OR = 3.440, CI = 1.082-10.937) Patients diagnosed with subclinical hypophosphatemia were encouraged to increase their intake of nuts and dairy products (25 patients) or reduce their alcohol intake (2), dose reduction of TDF (4) or placed under observation (4). Among patients with subclinical hypophosphatemia, serum phosphorus concentrations were elevated (>3.0 mg/dL) in 23 of 36 patients (63.8%). Increased nut and dairy intake increased phosphorus concentrations to more than 3.0 mg/dl in 16 of 25 patients (64.0%).Entecavir or tenofovir alafenamide fumarate (TAF) should be considered rather than TDF in patients with liver cirrhosis because of the risk of hypophosphatemia. Instead of stopping TDF treatment, encouraging increased intake of phosphorus-rich foods could increase serum phosphorus concentrations in clinical practice.

Efficacy and safety of telbivudine and tenofovir disoproxil fumarate in preventing hepatitis B vertical transmission: A real-life practice

Mother-to-child transmission (MTCT) is a major obstacle in the elimination of hepatitis B virus (HBV) infection. Telbivudine (LdT) and tenofovir disoproxil fumarate (TDF) are the two most common antiviral medicines for preventing MTCT. However, the efficacy and safety of LdT and TDF in preventing HBV vertical transmission during the second to third trimester have not been compared rigorously. Therefore, we carried out a prospective multicentre cohort study of chronic hepatitis B in mothers with HBV DNA > 10⁶  IU/mL, receiving LdT or TDF during the second to third trimester. Among the 893 mothers enrolled, 857 (LdT/TDF/untreated group (NTx) = 396/325/136) completed consecutive follow-up with 854 infants (LdT/TDF/NTx = 395/323/136). LdT and TDF treatment resulted in a similar decrease of HBV DNA in mothers at delivery. Multivariate analysis indicated that only HBsAg titre at the baseline correlated with viral DNA decrease (P = 0.015). With intention-to-treat analysis, MTCT rates in the LdT, TDF and NTx group were 4.41%, 2.42% and 22.08%, respectively. An increasing vertical transmission rate was found to be closely associated with higher HBsAg titre, 5.32% and 17.65% infection rate was estimated in infants born to mothers with HBsAg > 4 and >5 log₁₀ IU/mL, respectively. No serious side effects were reported in either mothers or infants. LdT and TDF treatments were well tolerated and showed comparable efficacy in reducing MTCT. Higher risk of MTCT was shown in pregnant women with HBsAg > 4 log₁₀ IU/mL.

Treatment Outcome and Renal Safety of 3-Year Tenofovir Disoproxil Fumarate Therapy in Chronic Hepatitis B Patients with Preserved Glomerular Filtration Rate

Background/Aims

To investigate the treatment efficacy and renal safety of long-term tenofovir disoproxil fumarate (TDF) therapy in chronic hepatitis B (CHB) patients with preserved renal function.

Methods

The medical records of 919 CHB patients who were treated with TDF therapy were reviewed. All patients had preserved renal function with an estimated glomerular filtration rate (eGFR) of at least 60 mL/min/1.73 m².

Results

A total of 426 patients (184 treatment-naïve and 242 treatment-experienced) were included for analysis. A virologic response (VR) was defined as achieving an undetectable serum hepatitis B virus (HBV) DNA level, and the overall VR was 74.9%, 86.7%, and 89.4% at the 1, 2, and 3-year follow-ups, respectively. Achieving a VR was not influenced by previous treatment experience, TDF combination therapy, or antiviral resistance. In a multivariate analysis, being hepatitis B e antigen positive at baseline and having a serum HBV DNA level ≥2,000 IU/mL at 12 months were associated with lower VR rates during the long-term TDF therapy. The overall renal impairment was 2.9%, 1.8%, and 1.7% at the 1, 2, and 3-year follow-ups, respectively. With regard to renal safety, underlying diabetes mellitus (DM) and an initial eGFR of 60 to 89 mL/min/1.73 m² were significant independent predictors of renal impairment.

Conclusions

TDF therapy appears to be an effective treatment option for CHB patients with a preserved GFR. However, patients with underlying DM and initial mild renal dysfunction (eGFR, 60 to 89 mL/min/1.73 m²) have an increased risk of renal impairment.

Pathologic femoral fracture due to tenofovir-induced Fanconi syndrome in patient with chronic hepatitis B: A case report

RATIONALE

We report a case of a hepatitis B virus (HBV)-positive patient with preexisting bone disease who developed tenofovir-induced Fanconi syndrome and subsequently sustained pathologic fracture. To our best knowledge, this is the first report in the English literature about pathologic femoral fracture due to tenofovir-induced Fanconi syndrome in patient with chronic hepatitis B (CHB). The present report describes detailed our experience with the diagnosis of pathologic femoral fracture due to tenofovir-induced Fanconi syndrome and treatment.

PATIENT CONCERNS

A 45-year-old man visited our hospital with pain in the right thigh region and gait disturbance which had started 3 months ago and worsened 1 week before admission. The patient was diagnosed with CHB in 2004. He was on lamivudine medication for 2 years. Medication for the patient was subsequently changed to adefovir in 2009 and tenofovir disoproxil fumarate (TDF) in 2013. He was on TDF since 2013.

DIAGNOSIS

His hip joint magnetic resonance imaging (MRI) revealed hypointensity lesions and cortical bone destruction in fat-saturated MR image at the iliopsoas muscle attachment site of the lesser trochanter of both femur. On blood test showed 25-OH vitamin D level at 6.42 ng/mL (normal range, >20 ng/mL) and U-deoxypyridinoline level at 7.60 nM/mMcr (normal range, 2.30-5.40 nM mMcr). However, osteocalcin and parathyroid hormone levels were within normal range. Based on these findings, the present case was concluded as tenoforvir-induced Fanconi syndrome.

INTERVENTIONS

TDF treatment was discontinued. After cooperation with internal medicine department, in order to prevent further fractures of the right lesser trochanter, internal fixation was performed under spinal anesthesia using compression hip nails (APIS, TDM, Korea).

OUTCOMES

Positive outcome by medication and operation demonstrates that his phosphorus and serum calcium levels were maintained within normal range and pain in the right thigh region was improved from visual analogue pain score (VAS) 7 before surgery to VAS 2 after surgery.

LESSONS

Physicians need to regularly monitor bone metabolism in patients with take in tenofovir for early diagnosis before its progression to pathologic fractures.

[A Case of Tenofovir-associated Fanconi Syndrome in Patient with Chronic Hepatitis B]

Tenofovir disoproxil fumarate (TDF) is one of the most widely used treatment options for human immunodeficiency virus (HIV) and HBV infections. Despite its efficacy and safety, some cases of nephrotoxicity have been reported in the treatment of HIV patients. Even more recently, very few cases of Fanconi syndrome associated with tenofovir therapy in HBV monoinfection have been reported. Herein, we report a case of a 47-year-old male with an HBV monoinfection, who developed Fanconi syndrome and a secondary osteomalacia with multiple bone pain. After TDF withdrawal and supplementation of calcitriol, his renal function was reverted. Although the overall risk of TDF-associated nephrotoxicity is very low, both glomerular and tubular function should be monitored in patients undergoing TDF treatment.

Clinical impact of the early alanine amininotransferase flare during tenofovir monotherapy in treatment-naïve patients with chronic hepatitis B

BACKGROUND/AIMS

Little is known about the effect of early flares on response during first-line tenofovir disoproxil fumarate (TDF) treatment for chronic hepatitis B (CHB). The aim of this study was to investigate the incidence and outcome of early alanine aminotransferase (ALT) flare in treatment-naive patients with CHB during long-term TDF monotherapy.

METHODS

One hundred eighty-one treatment-naive CHB patients were treated with a 300-mg once-daily dose of TDF for more than 12 weeks. Virological markers of hepatitis B virus (HBV) and biochemical data were measured at baseline and every 4-12 weeks during the therapy. The proportion of patients with undetectable HBV DNA level (< 100 copies/mL) was noted.

RESULTS

The median age was 48.3 years and 122 patients (67.4%) were men. Hepatitis B envelope antigen (HBeAg) was positive in 101 patients (55.8%). No patient had cirrhosis. The median follow-up duration was 45 weeks (12-155 weeks). ALT flare (>5 × upper limit of the normal range) occurred in seven patients (3%) without viral breakthrough within the first 8 weeks after the start of TDF monotherapy. Among them, six patients were HBeAg-positive and one patient was HBeAg-negative. All cases of early ALT flares resolved within 4 weeks and virologic response was observed in all patients without interruption or discontinuation of treatment.

CONCLUSIONS

Continuous TDF monotherapy was effective and safe in treatment-naive patients with CHB who experienced early ALT flares followed by a decrease in HBV DNA level.

Efficacy and safety of entecavir versus tenofovir treatment in chronic hepatitis B patients: A randomized controlled trial

AIM

Entecavir (ETV) and tenofovir disoproxil fumarate (TDF) are considered among the most potent antiviral agents for the treatment of chronic hepatitis B infection. We aimed to compare treatment efficacy and safety of ETV and TDF in nucleoside-naïve chronic hepatitis B patients.

METHODS

Inclusion criteria were compensated chronic hepatitis B patients who were either hepatitis B e antigen (HBeAg)-positive or HBeAg-negative. Exclusion criteria were co-infection with hepatitis C virus and/or HIV, concurrent malignancy, and decompensated cirrhosis. Virological, biochemical, and serological end-points at week 96 and 144 were compared. Of 400 patients, 200 patients received ETV and 200 received TDF.

RESULTS

There were no significant differences between the two groups in baseline characteristics including age (41.6 ± 11.5 vs. 41.2 ± 11.6, mean baseline hepatitis B virus DNA (5.91 ± 1.79 vs. 5.94 ± 1.68 log₁₀ IU/mL), mean baseline alanine aminotransferase (68.1 ± 64.1 vs. 76.8 ± 79.8 U/L), and cirrhosis (15.5% vs. 14.5%). At week 144 of treatment, 91 and 94% of the ETV and TDF groups, respectively, achieved undetectable hepatitis B virus DNA. In HBeAg-positive patients, HBeAg seroconversion could be achieved in 27.4% and 33.7% at week 144 for ETV and TDF groups, respectively. Quantitative hepatitis B surface antigen dropped significantly over 144 weeks of treatment period but only 1.0 to 1.5% experienced hepatitis B surface antigen loss. Safety profiles were consistent with previous reports of monotherapy.

CONCLUSION

Both ETV and TDF showed potent antiviral activity against hepatitis B. Either ETV or TDF can be recommended as a treatment of choice for patients with chronic hepatitis B. Both drugs were safe and well tolerated.

Effect of Entecavir and Tenofovir Treatment on Noninvasive Fibrosis Scores: Which One Is Better?

Liver biopsy is the best method for detecting fibrosis grade of the liver in chronic hepatitis B. However, the invasiveness of liver biopsy complicates its routine use in follow-up of treatment. We planned to determine the usage of fibrosis predicting noninvasive scores in the follow-up of the treatment of patients with chronic hepatitis B treated with entecavir or tenofovir. Two hundred twenty-eight patients with hepatitis B with liver biopsy were included in the study. Fibrosis grade was determined by Ishak score. The laboratory data at months 0, 12, and 24 during treatment were collected and noninvasive fibrosis scores (aspartate aminotransferase to alanine aminotransferase ratio [AAR], aspartate aminotransferase to platelet ratio index [APRI], fibrosis index based on the 4 factors [FIB-4] and red cell distribution width to platelet ratio [RPR]) were calculated. Statistically significant increase in all scores and decrease in platelet count were observed as the fibrosis level increased. For differentiation of patients with fibrosis ≥grade 2, the highest sensitivity and specificity rates were shown by APRI score (sensitivity 67%, specificity 69%, and cutoff ≥0.5). FIB-4 was the most successful score for differentiation of patients with fibrosis ≥grade 3 (sensitivity 83%, specificity 74%, and cutoff ≥1.45). A significant decrease in all noninvasive fibrosis scores was observed at months 12 and 24 during treatment with both entecavir and tenofovir (P < 0.001). Among these, only the improvement in APRI score was found better in entecavir group with statistical significance (P < 0.05). APRI score was effective in demonstrating early-stage fibrosis. FIB-4, RPR, and platelet count were better in demonstrating advanced fibrosis. Although noninvasive scores cannot replace liver biopsy for diagnosis, they can be used for monitoring the response to treatment.

Review article: long-term safety of nucleoside and nucleotide analogues in HBV-monoinfected patients

BACKGROUND

Nucleos(t)ide analogues (NUCs) for chronic hepatitis B treatment achieve high rates of viral suppression and are generally well tolerated. Entecavir (ETV) and tenofovir disoproxil fumarate (TDF) are the currently preferred first-line agents. The safety of these agents in clinical practice is particularly relevant since long-term treatment is usually required.

AIM

To summarise and critically discuss recent real-world evidence on the safety of treatment with ETV or TDF in hepatitis B virus (HBV)-monoinfected patients.

METHODS

PubMed and conference proceedings up to 15th June 2015 were searched using the terms ((((Hepatitis_B) OR HBV) AND ((tenofovir) OR entecavir)) AND (((lactic_acidosis) OR bone) OR renal)).

RESULTS

In selected populations included in registration studies, both ETV and TDF were well tolerated with no clinically significant renal toxicity or lactic acidosis. Growing 'real-world' clinical experience with these agents includes some reports of ETV-associated lactic acidosis and TDF-associated renal impairment; however, evidence from cohort studies appears to be conflicting. In the case of ETV-related lactic acidosis, a small number of cases have been reported, all in patients with decompensated cirrhosis. The degree of association between TDF treatment and changes in markers of renal function varies between studies: discrepancies may result from the use of different definitions and cut-offs for reporting renal toxicities, and differences in patient populations.

CONCLUSIONS

Pre-treatment and on-treatment monitoring of eGFR and phosphorus, with prompt appropriate dose adjustment or treatment switch can minimise the impact of NUC renal toxicity. Standardisation of measures of renal impairment and identification of early molecular markers remain an unmet need.

Tenofovir-associated nephrotoxicity in patients with chronic hepatitis B: two cases

Tenofovir disoproxil fumarate (TDF) is effective against chronic hepatitis B (CHB) infection and its use is increasing rapidly worldwide. However, it has been established that TDF is associated with renal toxicity in human immunodeficiency virus-infected patients, while severe or symptomatic TDF-associated nephrotoxicity has rarely been reported in patients with CHB. Here we present two patients with TDF-associated nephrotoxicity who were being treated for CHB infection. The first patient was found to have clinical manifestations of proximal renal tubular dysfunction and histopathologic evidence of acute tubular necrosis at 5 months after starting TDF treatment. The second patient developed acute kidney injury at 17 days after commencing TDF, and he was found to have membranoproliferative glomerulonephritis with acute tubular injury. The renal function improved in both patients after discontinuing TDF. We discuss the risk factors for TDF-associated renal toxicity and present recommendations for monitoring renal function during TDF therapy.

Comparison of renal safety and efficacy of telbivudine, entecavir and tenofovir treatment in chronic hepatitis B patients: real world experience

This study aims to assess the nephrotoxicity and efficacy of tenofovir disoproxil fumarate (tenofovir), telbivudine and entecavir. A retrospective study of 587 patients with chronic hepatitis B treated with tenofovir (n = 170), telbivudine (n = 184) and entecavir (n = 233) for at least 1 year. Renal function and efficacy were assessed. The estimated glomerular filtration rate (eGFR) decreased significantly in the tenofovir group after a mean of 17 months treatment (from 92.2 to 85.6 mL/min/1.73 m(2), p < 0.001), but increased in the telbivudine group after a mean of 32 months of treatment (from 86.1 to 95 mL/min/1.73 m(2), p < 0.001). There was no significant change in eGFR in the entecavir group after a mean of 44 months. By multivariate analysis, pre-existing renal insufficiency (p = 0.003), tenofovir (p = 0.007) and diuretic treatment (p = 0.001) were independent predictors for renal function deterioration. Cumulative virological breakthrough was 0% in tenofovir after 2 years, 3.4% in entecavir after 7 years and 22.9% in telbivudine after 5 years. Liver cirrhosis (p = 0.008) and virological breakthrough (p = 0.040) were independently associated with increased risk of hepatocellular carcinoma development. Tenofovir may lead to deterioration in renal function as assessed by serial eGFR measurements. Although telbivudine appeared to be associated with an improvement in eGFR, it was associated with high rates of virological breakthrough, which was an independent risk factor for HCC development. With low rates of virological breakthrough and preservation of renal function, entecavir could be the best choice among these three agents.

Tenofovir versus entecavir in treatment of chronic hepatitis B virus with severe acute exacerbation

Tenofovir disoproxil fumarate (TDF) and entecavir (ETV) are effective antivirals recommended as first-line monotherapies for treatment of chronic hepatitis B (CHB) infection. This study aimed to compare the short-term efficacies of TDF and ETV in the treatment of CHB with severe acute exacerbation. From 2008 to 2013, 189 consecutive treatment-naive CHB patients receiving TDF (n = 41) or ETV (n = 148) for severe acute exacerbation were enrolled. The primary endpoint was overall mortality or receipt of liver transplantation by week 24. The baseline characteristics were comparable between these two groups. By week 24, 8 (19% [95% confidence interval {CI}, 7% to 32%]) patients in the TDF group and 26 (18% [95% CI, 11 to 24%]) patients in the ETV group died (n = 30) or received liver transplantation (n = 4) (P = 0.749). The two groups of patients developed similar rates of liver-related complications and achieved comparable biochemical and virological responses at week 24. Cox regression analysis showed that baseline viral DNA level (P = 0.002), hypertension (P = 0.002), model for end-stage liver disease (MELD) score (P = 0.01), platelet count (P = 0.005), early presence (within 4 weeks) of ascites (P = 0.005), hepatic encephalopathy (P = 0.002), and hepatorenal syndrome (P < 0.001) were independent factors for mortality or liver transplantation. Among the patients who survived by week 24, there was no difference between the two groups in the percentage of patients who had a serum creatinine increase of ≥0.5 mg/dl from baseline (6.7% [95% CI, 0% to 16%] versus 2.0% [95% CI, 0% to 4.8%] in the TDF and ETV groups, respectively; P = 0.231), whereas a significant reduction in the estimated glomerular filtration rate (eGFR) was found in the two groups (P = 0.001 for both). In conclusion, TDF and ETV produce a similar treatment response and clinical outcome in patients with severe acute exacerbation of CHB.

Entecavir has high efficacy and safety in white patients with chronic hepatitis B and comorbidities

OBJECTIVES

The aim of this study was to evaluate the efficacy and safety of entecavir monotherapy in nucleos(t)ide-naive chronic hepatitis B patients and to analyse the influence of the comorbidity burden on therapy outcome.

METHODS

We retrospectively analysed data from 237 nucleos(t)ide-naive chronic hepatitis B white patients treated with entecavir (0.5 mg/day) at 23 Spanish centres. For the efficacy and safety analyses, patients were grouped according to their baseline comorbidities.

RESULTS

The mean age of the cohort was 43 years (range: 19-82 years); 73% were male, 83% were white, and 33% were hepatitis B e antigen (HBeAg) positive. At baseline, the median hepatitis B virus DNA level was 6.20 log10 IU/ml. Of the patients, 18% had cirrhosis, 9.7% had diabetes, 16.3% had hypertension, and 15.7% had obesity; 13.4% of patients had more than one comorbid condition. Virological and biochemical responses at month 36 were obtained independently of the patients' baseline comorbid condition. Of 10 HBeAg-positive patients who discontinued treatment after HBeAg seroconversion, those who had not also cleared HBsAg (six) experienced virological recurrence in a median 5.6 months. There were no treatment discontinuations due to adverse events. Three patients were diagnosed with hepatocellular carcinoma at months 12, 30 and 54, and six experienced hepatic decompensation during follow-up. The median serum creatinine levels did not increase after 36 months of treatment, even in patients with comorbidities.

CONCLUSION

Entecavir is safe, well tolerated, and highly effective, even in patients with comorbid condition(s). Discontinuation of treatment in patients who have not been cleared of HBsAg may lead to virological recurrence.

Tenofovir disoproxil fumarate monotherapy for nucleos(t)ide-naïve chronic hepatitis B patients in Korea: data from the clinical practice setting in a single-center cohort

BACKGROUND/AIMS

This study assessed the antiviral efficacy and safety of tenofovir disoproxil fumarate (TDF) for up to 12 months in Korean treatment-naïve chronic hepatitis B (CHB) patients.

METHODS

A total of 411 treatment-naïve CHB patients who had been treated with TDF for at least 3 months (median 5.6) were consecutively enrolled. Clinical, biochemical, virological parameters and treatment adherence were routinely assessed every 3 months.

RESULTS

The median age was 51.3 years, 63.0% of the patients were male, 49.6% were HBeAg (+), and 210 patients had liver cirrhosis. The median baseline HBV DNA was 5.98 (SD 1.68) log10 IU/mL. Among the patients completing week 48, 83.3% had a complete virologic response (CVR, <12 IU/mL by HBV PCR assay), and 88.2% had normalized levels of alanine aminotransferase (ALT). The cumulative probabilities of CVR at 3, 6, 9 and 12 months were 22.8%, 53.1%, 69.3% and 85.0%. During the follow-up period, 9.8% patients achieved HBeAg loss and 7.8% patients achieved HBeAg seroconversion. There was no virological breakthrough after initiating TDF. The most common TDF-related adverse event was gastrointestinal upset, and three patients discontinued TDF therapy. However, no serious life-threatening side effect was noted.

CONCLUSIONS

In a clinical practice setting, TDF was safe and highly effective when administered for 12 months to Korean treatment-naïve CHB patients.

Efficacy and safety of tenofovir disoproxil fumarate in pregnancy to prevent perinatal transmission of hepatitis B virus

BACKGROUND & AIMS

Perinatal transmission of hepatitis B virus still occurs despite immunoprophylaxis in approximately 9% of children from highly viraemic mothers. Antiviral therapy in this setting has been suggested, however with limited evidence to direct agent choice.

METHODS

We conducted a multi-centre, prospective, opt-in observational study of antiviral safety and efficacy in pregnant women with high viral load (>7 log IU/ml); lamivudine was used from 2007 to 2010 and tenofovir disoproxil fumarate (TDF) from late 2010. Outcomes of treated and untreated cohorts were compared.

RESULTS

120 women with 130 pregnancies used TDF (58), lamivudine (52 including four who switched due to TDF intolerance) and no therapy (20). 96% were HBeAg positive, with baseline viral load mean 7.8 log IU/ml (±0.72) and ALT median 25 U/L (18.75-33). Duration of antiviral theraphy before birth was mean 58 days (±19) TDF and 53 (±14) lamivudine. Viral load declined by 3.64 log IU/ml (±0.9) TDF and 2.81 log IU/ml (±1.33) lamivudine. Virologic failure (birth viral load >7 IU/ml) occurred in 3% and 18% respectively. Congenital abnormality rate and neonatal growth centiles were similar across cohorts. Perinatal transmission reduced significantly to 2% and 0% in TDF and lamivudine cohorts, compared with 20% in untreated.

CONCLUSIONS

TDF in this setting is safe, effective and more potent than lamivudine. Antiviral therapy did not adversely impact obstetric or infant parameters. More TDF intolerance occurred than expected. Perinatal transmission was significantly reduced in antiviral therapy cohorts.

Comparison of efficacy and safety of tenofovir and entecavir in chronic hepatitis B virus infection: a systematic review and meta-analysis

OBJECTIVE

Tenofovir (TDF) and entecavir (ETV) are both potent antiviral agents for the treatment of chronic hepatitis B virus (HBV) infection. Multiple studies have compared efficacy and safety of these two agents, but yielded inconsistent results. Hence, we conducted a meta-analysis to discern comparative efficacy and safety.

METHODS

Published data relevant to a comparison of TDF and ETV used in HBV were included. HBV DNA suppression rate, ALT normalization rate, and HBeAg seroconversion rate at 24 weeks and 48 weeks were reviewed. Drug safety profiles and resistance were also discussed.

RESULTS

Seven articles met entry criteria. Four and six articles included data for 24 and 48-week HBV DNA suppression rates, respectively, and no significant differences for the rates between the two drugs were found in chronic HBV patients (TDF vs. ETV: relative risk [RR] = 1.10, 95% CI = 0.91-1.33 and RR = 1.07, 95% CI = 0.99-1.17 for 24 weeks and 48 weeks, respectively). For the ALT normalization rate (three studies for 24 weeks, four articles for 48 weeks) and HBeAg seroconversion rate (two and four studies for 24 weeks and 48 weeks, respectively), no difference was observed between TDF and ETV. Additionally, no significant distinction in short term safety was found for CHB patients.

CONCLUSIONS

TDF and ETV are similarly effective and safe in chronic HBV patients after 24 weeks and 48 weeks of anti-viral therapy. Nevertheless, the long-term efficacy and safety of TDF and ETV should be monitored in prolonged therapy.

A cost-utility analysis of drug treatments in patients with HBeAg-positive chronic hepatitis B in Thailand

BACKGROUND

Only lamivudine has been included for patients with chronic hepatitis B (CHB) in the National List of Essential Drugs (NLED), a pharmaceutical reimbursement list in Thailand. There have also been no economic evaluation studies of CHB drug treatments conducted in Thailand yet. In order to fill this gap in policy research, the objective of this study was to compare the cost-utility of each drug therapy (Figure 1) with palliative care in patients with HBeAg-positive CHB.

METHODS

A cost-utility analysis using an economic evaluation model was performed to compare each drug treatment for HBeAg-positive CHB patients. A Markov model was used to estimate the relevant costs and health outcomes during a lifetime horizon based on a societal perspective. Direct medical costs, direct non-medical costs, and indirect costs were included, and health outcomes were denoted in life years (LYs) and quality-adjusted life years (QALYs). The results were presented as an incremental cost effectiveness ratio (ICER) in Thai baht (THB) per LY or QALY gained. One-way sensitivity and probabilistic sensitivity analyses were applied to investigate the effects of model parameter uncertainties.

RESULTS

The ICER values of providing generic lamivudine with the addition of tenofovir when drug resistance occurred, generic lamivudine with the addition of tenofovir based on the road map guideline, and tenofovir monotherapy were -14,000 (USD -467), -8,000 (USD -267) , and -5,000 (USD -167) THB per QALY gained, respectively. However, when taking into account all parameter uncertainties in the model, providing generic lamivudine with the addition of tenofovir when drug resistance occurred (78% and 75%) and tenofovir monotherapy (18% and 24%) would yield higher probabilities of being cost-effective at the societal willingness to pay thresholds of 100,000 (USD 3,333) and 300,000 (USD 10,000) THB per QALY gained in Thailand, respectively.

CONCLUSIONS

Based on the policy recommendations from this study, the Thai government decided to include tenofovir into the NLED in addition to generic lamivudine which is already on the list. Moreover, the results have shown that the preferred treatment regimen involves using generic lamivudine as the first-line drug with tenofovir added if drug resistance occurs in HBeAg-positive CHB patients.

Ester prodrugs of acyclic nucleoside thiophosphonates compared to phosphonates: synthesis, antiviral activity and decomposition study

9-[2-(Thiophosphonomethoxy)ethyl]adenine [S-PMEA, 8] and (R)-9-[2-(Thiophosphonomethoxy)propyl]adenine [S-PMPA, 9] are acyclic nucleoside thiophosphonates we described recently that display the same antiviral spectrum (DNA viruses) as approved and potent phosphonates PMEA and (R)-PMPA. Here, we describe the synthesis, antiviral activities in infected cell cultures and decomposition study of bis(pivaloyloxymethoxy)-S-PMEA [Bis-POM-S-PMEA, 13] and bis(isopropyloxymethylcarbonyl)-S-PMPA [Bis-POC-S-PMPA, 14] as orally bioavailable prodrugs of the S-PMEA 8 and S-PMPA 9, in comparison to the equivalent "non-thio" derivatives [Bis-POM-PMEA, 11] and [Bis-POC-PMPA, 12]. Compounds 11, 12, 13 and 14 were evaluated for their in vitro antiviral activity against HIV-1-, HIV-2-, HBV- and a broad panel of DNA viruses, and found to exhibit moderate to potent antiviral activity. In order to determine the decomposition pathway of the prodrugs 11, 12, 13 and 14 into parent compounds PMEA, PMPA, 8 and 9, kinetic data and decomposition pathways in several media are presented. As expected, bis-POM-S-PMEA 13 and bis-POC-S-PMPA 14 behaved as prodrugs of S-PMEA 8 and S-PMPA 9. However, thiophosphonates 8 and 9 were released very smoothly in cell extracts, in contrast to the release of PMEA and PMPA from "non-thio" prodrugs 11 and 12.

Considerations for the long-term treatment of chronic hepatitis B with nucleos(t)ide analogs

Treatment of chronic hepatitis B (CHB) with nucleos(t)ide analogs is often required over a prolonged period to achieve durable virologic suppression. One barrier to the success of long-term therapy is the emergence of drug-resistant mutants. Current guidelines therefore recommend the most potent drugs with optimal resistance profiles, that is, entecavir and tenofovir are used as first-line monotherapies in CHB. Characteristics of the hepatitis B virus, the disease, the patient and the drug can influence the response to antiviral treatment and risk of relapse. This review discusses factors to consider maximizing the chances of successful long-term treatment of CHB, and provides an overview of the long-term efficacy and safety data that have become available over the 4-5 years since entecavir and tenofovir were first approved for the treatment of CHB. Recent findings on whether and under what circumstances long-term therapy of CHB might be stopped are also discussed.

Long-term therapy with nucleoside/nucleotide analogues for chronic hepatitis B in Asian patients

Of the estimated 400 million patients with chronic hepatitis B (CHB) globally, approximately 75% are Asians, representing a clinically important subgroup with a higher risk of cirrhosis and hepatocellular carcinoma than Caucasian patients. This review summarizes recent data from clinical long-term and real-life studies of entecavir and tenofovir, the recommended first-line oral therapies for treating CHB, in nucleoside/nucleotide-naive Asian CHB patients with compensated or decompensated liver disease. Long-term treatment with entecavir or tenofovir achieved profound and durable virological suppression, and led to improved liver histology and function. The data presented in this review will help physicians in making evidence-based decision choices regarding first-line antiviral therapy and long-term management in Asian CHB patients.

Efficacy of entecavir with or without tenofovir disoproxil fumarate for nucleos(t)ide-naïve patients with chronic hepatitis B

BACKGROUND & AIMS

Entecavir (ETV) and tenofovir disoproxil fumarate (TDF) are potent antiviral agents that might have additive or synergistic antiviral activity in treatment of patients with chronic hepatitis B (CHB). We compared the efficacy and safety of ETV monotherapy with those of a combination of ETV and TDF.

METHODS

We performed a randomized, open-label, multicenter, superiority study of 379 nucleos(t)ide-naïve patients with hepatitis B e antigen (HBeAg)-positive (n = 264) or HBeAg-negative (n = 115) CHB. Subjects were given ETV 0.5 mg (n = 182) or a combination of ETV 0.5 mg and TDF 300 mg (n = 197) for 100 weeks.

RESULTS

At week 96, comparable proportions of patients in each study arm achieved the primary end point of a level of hepatitis B virus (HBV) DNA <50 IU/mL (83.2% vs 76.4%; P = .088). Among HBeAg-positive patients, a greater proportion given combination therapy achieved levels of HBV DNA <50 IU/mL than those given ETV alone (80.4% vs 69.8%; P = .046). However, this difference was observed only in patients with baseline levels of HBV DNA ≥ 10(8) IU/mL (79% vs 62%) and not in those with baseline levels of HBV DNA <10(8) IU/mL (83% in both arms). Rates of HBeAg loss and HBeAg seroconversion were comparable between groups, whereas the rate of alanine aminotransferase normalization was greater in the ETV monotherapy group. No HBV variants associated with ETV or TDF resistance were detected. Safety profiles were consistent with previous reports of ETV or TDF monotherapy.

CONCLUSIONS

The antiviral efficacy of ETV monotherapy is comparable to that of ETV plus TDF in a mixed population of nucleos(t)ide-naïve patients with CHB (70% HBeAg positive). The combination therapy could provide an incremental benefit to HBeAg-positive patients with baseline levels of HBV DNA ≥ 10(8) IU/mL.

Similar risk of renal events among patients treated with tenofovir or entecavir for chronic hepatitis B

BACKGROUND & AIMS

Tenofovir is a nucleotide reverse-transcriptase inhibitor approved for treatment of human immunodeficiency virus infection, as well as chronic hepatitis B (CHB). We evaluated nephrotoxicity among patients with CHB treated with tenofovir.

METHODS

We performed a community-based, retrospective cohort study of 80 patients with CHB who received tenofovir, alone or in a combination regimen; they were matched for age and sex with 80 CHB patients who received only entecavir. Incidences of serum creatinine (SCr) increase ≥0.2 mg/dL and new SCr levels of 1.5, 2.0, or 2.5 mg/dL were assessed. Patients with an estimated glomerular filtration rate (eGFR) <60 mL/min, calculated using the Modification of Diet in Renal Disease or Cockcroft-Gault formula, or who had ≥20% decrease in eGFR were also recorded.

RESULTS

More patients given entecavir had increases in SCr ≥2.5 mg/dL (1 vs 6; P = .053), whereas more patients given tenofovir had a new Cockcroft-Gault eGFR of <60 mL/min (15 vs 6; P = .022) and at least 1 dose adjustment (13 vs 4; P = .021). By multivariate analysis, the only significant factors associated with an increase in SCr were a history of organ transplantation (adjusted odds ratio, 6.740; 95% confidence interval, 1.799-28.250; P = .005) and pre-existing renal insufficiency (adjusted odds ratio, 10.960; 95% confidence interval, 2.419-48.850; P = .002). No factors, including therapy assignment, were associated with a new eGFR <60 mL/min.

CONCLUSIONS

Markers of renal function indicated that patients who received tenofovir were no more likely to have changes in renal function than patients treated with entecavir. History of transplant and pre-existing renal insufficiency were the only factors independently associated with increases in SCr.

First-line treatment of chronic hepatitis B with entecavir or tenofovir in 'real-life' settings: from clinical trials to clinical practice

Entecavir (ETV) and tenofovir disoproxil fumarate (TDF) are potent nucleos(t)ide analogues (NUCs) recommended as first-line monotherapies for chronic hepatitis B. In Phase III trials, ETV and TDF demonstrated superior efficacy, and comparable safety compared with other NUCs. In long-term clinical studies, both drugs achieved virologic response rates of around 95%, with very low rates of resistance development and good safety profiles. Clinical trials are conducted under standardized conditions with strict enrolment criteria that limit the heterogeneity of study populations. 'Real-life' populations tend to be composed of a wider range of patients, often older and with different morbidities, comorbidities that may impact treatment efficacy and co-factors, such as smoking and alcohol intake, which can have a direct impact on disease progression. Real-life studies provide better representations of everyday clinical practice and are important to confirm the results reported in clinical studies and to identify rare or late-emerging adverse events. In five 'real-life' studies of ETV in more than 1000 patients, up to 4 years of treatment resulted in virologic responses in 76-96% of patients. Two real-life studies of TDF reported response rates of 71-92% after up to 21 months of treatment. Low incidences of drug resistance and favourable tolerabilities were reported for both drugs, thus confirming the results from registration trials.

Acyclic nucleoside thiophosphonates as potent inhibitors of HIV and HBV replication

9-[2-(Thiophosphonomethoxy)ethyl]adenine 3 and (R)-9-[2-(Thiophosphonomethoxy)propyl]adenine 4 were synthesized as the first thiophosphonate nucleosides bearing a sulfur atom at the α-position of the acyclic nucleoside phosphonates PMEA and PMPA. Thiophosphonates S-PMEA 3 and S-PMPA 4 were evaluated for in vitro activity against HIV-1 (subtypes A to G), HIV-2 and HBV-infected cells, and found to exhibit potent antiretroviral activity. We showed that their diphosphate forms S-PMEApp 5 and S-PMPApp 6 are readily incorporated by wild-type (WT) HIV-1 RT into DNA and act as DNA chain terminators. Compounds 3 and 4 were evaluated for in vitro activity against a broad panel of DNA and RNA viruses and displayed beside HIV a moderate activity against herpes simplex virus and vaccinia viruses. In order to measure enzymatic stabilities of the target derivatives 3 and 4, kinetic data and decomposition pathways were studied at 37 °C in several media.