Although nucleos(t)ide analogue (NA) therapy can effectively suppress HBV replication, the ideal therapeutic endpoints, including hepatitis B surface antigen(HBsAg) seroclearance, is difficult to achieve.(1) Therefore, chronic hepatitis B (CHB) patients often require long-term HBV suppression to achieve the therapeutic goals, with the adherence to long-term NA therapy being an important clinical issue.(2, 3) ETV is one of the standard treatments for CHB,(4, 5) but its absorption can be significantly reduced by food.(6) ETV users must take the pills two hours before or after meals, and the blood level of ETV may thus be affected if this recommendation is not fully followed.In addition, the metabolism of ETV is involved by renal excretion, therefore the dosage of ETV should be adjusted according to renal function.(7) For example, among patients in chronic kidney disease (CKD) stage 4, i.e.,eGRF15-29 ml/min/1.73m, the frequency of ETV taking should be reduced from once daily to every 72-96 hours, which may be forgettable and inconvenient to ETV users.However, the adherence of NA therapy is an essential part for long-term HBV suppression, and the efficacy of ETV therapy may be affected by the reduced adherence during long-term therapy.

Except ETV, TAF is also a HBV antiviral recommended by the current practice guidelines in the treatment of CHB, with a high potency in antiviral efficacy and low rate in virological resistance.(4, 5) In addition, TAF can be a 2nd-line rescue antiviral recommendation for HBV with resistance to ETV therapy.(4, 5) Moreover, because TAF is formulated to deliver the active metabolite to target cells more efficiently than tenofovir disoproxil fumarate (TDF) at a much lower dose, thereby reducing systemic exposure to tenofovir. In the randomized controlled trials,(8, 9) patients in the TAF arm had improved renal function and bone marrow density (BMD),as compared to patients in the TDF arm. Furthermore, in some retrospective studies, switching from ETV to TAF may present a superior efficacy in HBV DNA suppression and HBsAg level reduction,(10-13) and renal safety was comparable between the TAF switch group and the ETV continuation group.(10, 11) Interestingly, switching from ETV to TAF is associated with improvement of the medication adherence,(6) which may be particularly important to patients under long-term NA therapy.

In a small retrospective study conducted in Japan,(14) medication adherence and satisfaction were compared between before and after switch antiviral therapy in patients who switched to TAF from ETV (n = 15), and medication adherence was found to be significantly improved (P = 0.04). In a prospective study aimed to evaluate the changes of serum HBsAg levels during a 48-week period after switching ETV to TAF,(6) the degree of HBsAg reduction was higher during the TAF administration period than during the ETV administration period in patients without cirrhosis, with genotype B HBV, or with undetectable serum hepatitis B core-related antigen (HBcrAg).The HBV cccDNA-related biomarkers, such as quantitative HBsAg (qHBsAg) or HBcrAg, have been considered important outcome predictors.(15, 16) With expected adherence improvement in TAF switch therapy, the changes of above-mentioned biomarkers may be improved. The investigators therefore aim to conduct a prospective cohort study of TAF switch therapy for CHB patients who are unsatisfied to ETV therapy.