Switching From Tenofovir Disoproxil Fumarate(TDF) to Tenofovir AlaFenamide(TAF) vs. Maintaining TDF Monotherapy in Chronic Hepatitis B Patients With Genotypic Resistance to Adefovir or Entecavir

Detailed Summary

Treatment of CHB patients with genotypic resistance to NUCs has been problematic due to the lack of data from randomized trials. Recently, two randomized trials comparing the efficacy of TDF monotherapy versus TDF and ETV combination therapy in CHB patients with documented genotypic resistance to adefovir (ADV) or ETV demonstrated TDF monotherapy was not statistically different in viral suppression at week 48 of treatment.1,2 The extension study based on the above two trials merged study subjects from these trials with changing from TDF and ETV combination group to TDF monotherapy to evaluate long-term efficacy and safety of TDF monotherapy for multidrug-resistant patients. At the time of merging of 192 subjects, by intention-to-treat analysis, 66.3% of TDF group and 68.0% of TDF-ETV group had virological response as determined by serum HBV DNA \<15 IU/mL. (in press) Three year long-term follow up study showed that the proportion of virologic suppression increased to 76.8% and 72.2% in TDF-TDF and TDF/TDF-ETV groups, respectively( P=0.46). (in press) TAF, a novel prodrug of tenofovir was developed to have greater stability in plasma than TDF, thereby enabling more efficient delivery of the active metabolite to target cells at a substantially lower dose. The reduced systemic exposure of tenofovir offers the potential for an improved safety profile compared to TDF a benefit that demonstrated in a recent clinical trial in patients with HIV infection. In a recent double-blind randomized phase 3 noninferiority trial with 873 treatment naive patients who were positive for HBeAg, the proportion of patients receiving TAF who had HBV DNA \<29 IU/mL at week 48 was 64%, which was non-inferior to the rate of 67% in patients receiving TDF (P=0.25).3 In the safety profile, TAF group had significantly smaller decrease in BMD than TDF group in the hip and spine, as well as significantly smaller increases in serum creatinine at week 48.3 For treatment naive HBeAg negative patients, a recent study with 425 subjects applied the same methodology and showed noninferiority in efficacy of TAF compared to TDF at week 48.4 Considering noninferiority in efficacy and superior bone and renal safety from TAF, TAF might be considered preferred choice of NUC instead of TDF. However, it is still unknown whether TAF would show similar efficacy and safety profile in patients with multidrug-resistant CHB.

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