Hepatitis B virus resistance to adefovir in a nucleotide naive patient with chronic hepatitis B virus infection

Selection of chronic hepatitis B therapy with high barrier to resistance

Antiviral drug resistance is a crucial factor that frequently determines the success of long-term therapy for chronic hepatitis B. The development of resistance to nucleos(t)ide analogues has been associated with exacerbations in liver disease and increased risk of emergence of multidrug resistance. The selection of a potent nucleos(t)ide analogue with a high barrier to resistance as a first-line therapy, such as entecavir or tenofovir, provides the best chance of achieving long-term treatment goals and should be used wherever possible. The barrier to resistance of a given nucleos(t)ide analogue is influenced by genetic barrier, drug potency, patient adherence, pharmacological barrier, viral fitness, mechanism of action, and cross-resistance. In countries with limited health-care resources, the selection of a therapy with a high barrier to resistance is not always possible and alternative strategies for preventing resistance might be needed, although limited data are available to support these strategies.

Management options for lamivudine-resistant chronic hepatitis B patients with suboptimal virological suppression by adefovir

BACKGROUND

In chronic hepatitis B (CHB) patients, adefovir is commonly used as a rescue therapy for lamivudine resistance, but often results in incomplete virological suppression.

AIM

To study the factors predicting response to adefovir rescue, and the treatment response of tenofovir and entecavir in suboptimal responders to adefovir in CHB patients.

METHODS

Chronic hepatitis B patients who took adefovir for at least 6 months for lamivudine resistance were studied. Early virological response was defined as undetectable HBV DNA at month 6. Maintained virological response was defined as undetectable HBV DNA till the last follow-up.

RESULTS

Among 136 patients on adefovir for 39 (5-117) months, 30 (22%) had early virological response. The 3-year cumulative probability of maintained virological response was similar between patients on adefovir monotherapy (n = 53, 57.9%) and those on combination of lamivudine and adefovir treatment (n = 83, 56.5%). The month 6 HBV DNA was the only independent factor associated with maintained virological response (adjusted hazard ratio 0.49, 95% confidence interval 0.37-0.65, P < 0.001). Twenty-six of 30 (87%) early responders and 36 of 106 (34%) non-early responders had maintained virological response on adefovir (P < 0.001). Among 106 non-early responders, 18 and 11 were switched to tenofovir and entecavir, respectively. The 1-year cumulative probability of maintained virological response was higher in patients switched to tenofovir (87.5%) than those switched to entecavir (37.5%; P = 0.048) or continued with adefovir (8.7%; P < 0.001).

CONCLUSIONS

In adefovir rescue for lamivudine resistance, month 6 HBV DNA predicts maintained virological response in CHB patients. Switching to tenofovir achieved best viral suppression among suboptimal responders to adefovir.

Adefovir dipivoxil resistance patterns in patients with lamivudine-resistant chronic hepatitis B

Background

Lamivudine (3TC)-resistant chronic hepatitis B patients demonstrated a higher rate of adefovir dipivoxil (ADV) resistance compared with nucleoside-naive patients. This study describes ADV mutation patterns in 3TC-resistant patients treated with ADV+3TC or ADV monotherapy, investigating whether mutations selected during 3TC therapy predispose to ADV resistance. Risk factors for ADV resistance were also evaluated.

Methods

A total of 60 3TC-experienced patients were treated with (or switched to) ADV monotherapy (30 patients) or ADV+3TC combination therapy (30 patients), and followed for at least 12 months. In all patients the hepatitis B virus reverse transcriptase (RT) region was amplified and directly sequenced before initiating ADV. The RT sequence was reevaluated for virological breakthrough patients and phenotypic analysis was performed for several patients.

Results

In total, 14 (23%) patients showed virological breakthrough (10/30 on ADV monotherapy and 4/30 on ADV+3TC). ADV resistance mutations (rtA181V/T and rtN236T) were detected alone or in combination for 11/14 patients, whereas novel substitutions were present in 3 patients. Before ADV treatment, apart from 3TC resistance signature mutations, additional changes were found, including the rtA181T mutation, which was already present in 2/14 ADV-resistant patients.

Conclusions

Although most patients showed virological breakthrough because of the well known rtA181V/T and rtN236T substitutions, more complex patterns were also found. ADV monotherapy, dose reduction and suboptimal virological response after 48 weeks of therapy were significantly associated with ADV resistance.