The goals of treating children with chronic hepatitis B (CHB) are to suppress viral replication, so as to normalize liver histopathology, and to prevent liver cirrhosis and hepatocellular carcinoma. The drugs approved by the US Food and Drug Administration (FDA) for the treatment of hepatitis B virus (HBV) in children include interferon-α (IFN-α), lamivudine (LAM), adefovir (ADV), and, most recently, entecavir (ETV).
Presently, treatment of CHB in children is initiated with IFN-α or LAM (1); however, approach to optimal therapy in children is inadequate because of inappropriate drugs available. IFN-α treatment has limitations, including relatively higher adverse events and lower rate of efficacy (2). LAM is safe and effective in children, but the development of LAM-resistant mutations is a major problem. The HBeAg seroconversion rate was variably noticed in 23% of children and 65% after 1 and 2 years of treatment by different studies (2,3). LAM-resistant HBV mutation was detected in 10% to 19% of children, and in 23% to 69.4% of children after 1 to 2 years of treatment, respectively (2,4,5).
Management of drug-resistant chronic HBV infection in children is particularly challenging because of the limited number of therapeutic options labeled for use in children (6). Presently, entecavir becomes a first-line option in most HBV treatment guidelines, but is only labeled for use in children ages 16 years and older, and resistance to LAM is a risk factor for entecavir resistance.
At present, there are a number of treatment guidelines for drug resistance in adults, including the 2009 European Association for the Study of the Liver (EASL) guidelines, the 2009 American Association for the Study of Liver Diseases (AASLD) guidelines, the 2008 US Panel guidelines, and the 2008 Asia-Pacific Steering Committee guidelines (1,7,8); however, there is no consensus among these guidelines for treating children with LAM-resistant mutants.
The endpoint of treating LAM resistance is achieving undetectable HBV-DNA to avoid further resistance of the virus and to achieve seroconversion. Until now, only a few clinical studies have demonstrated the efficacy of add-on second drug compared with switching to other antiviral agents for the treatment of children and adolescents with LAM-resistant CHB. In the present study, we compared the virologic responses to the combination of LAM and adefovir with entecavir monotherapy in children and adolescents with CHB who had developed resistance to LAM.
Between January 2008 and January 2012, 27 children and adolescents developed LAM resistance during consecutive LAM monotherapy. Of these 27 patients, 8 patients (ages 2.1–20.6 years) were treated with a combination of LAM (3 mg · kg−1 · day−1, maximum dose of 100 mg) and adefovir (0.3 mg · kg−1 · day−1, maximum dose of 10 mg), whereas 8 patients (ages 4.1–16.7 years) were switched to entecavir (0.03 mg · kg−1 · day−1, maximum dose of 1 mg/day) monotherapy without randomization and 11 patients (age 4.4–17.7 years) were switched to ADV (0.3 mg · kg−1 · day−1, maximum dose of 10 mg) alone, as a historical control. All of the patients were treated and followed for a mean period of 31.7 months (11.6–69.3 months) at a single center (Department of Pediatrics, Kyungpook National University Hospital, Daegu, Republic of Korea). The present study was approved by the institutional review board, and written informed consent was obtained from the patients or from the patients’ parents.
Inclusion and Exclusion Criteria
All of the patients formerly treated with LAM had been HBsAg and HBeAg positive, anti-HBs and HBe negative, had had elevated HBV-DNA (>10 pg/mL, with a lower limit of detection of 0.5 pg/mL) for at least 6 months, and had had serum alanine aminotransferase (ALT) values more than 1.3 times ULN (times the upper limit of the normal range) for at least 3 months without a 1-log drop of HBV-DNA decrement before treatment.
Patients were not included in the present study, if they were coinfected with hepatitis C virus, had been treated with immunosuppressive drugs, cytotoxic agents, corticosteroids, or systemic antiviral agents in the last 6 months before initiation of LAM treatment, and had decompensated liver diseases or other chronic liver diseases. Patients younger than 2 years or older than 20 years and having low hepatitis B DNA levels (<357 IU/mL) at the time of adding adefovir to ongoing LAM or switching to entecavir or adefovir were also excluded from the study.
Definition of LAM resistance is reemergence of HBV-DNA after HBV-DNA clearance, which was confirmed 2 times by 3-month interval or detection of HBV mutations and viral breakthrough defined as ≥1 log10/IU/mL increase in serum HBV-DNA levels compared to nadir (<2 log10/IU/mL decrease after LAM treatment). Definition of adefovir or entecavir resistance is the same as that of LAM.
Treatment and Follow-up of Patients
All of the patients were monitored every 2 to 3 months, and the importance of compliance with the therapy was emphasized before and during the treatment. At every visit, clinical examination, biochemical (AST, ALT) assessment, and virologic (HBV-DNA level, HBsAg, anti-HBs, HBeAg, anti-HBe) assessment were performed. To assess therapeutic efficacy, the periods for HBV-DNA titer decrement (>1 log10, >2 log10) and HBV-DNA clearance (<357 IU/mL) were estimated. HBsAg, HBeAg, and antibodies were determined by using commercially available electrochemiluminescence immunoassay (ECLIA method, Roche Diagnostics, Indianapolis, IN). HBV-DNA was determined by real-time polymerase chain reaction (PCR) (Roche COBAS AmpliPrep/TaqMan96 real-time PCR assay, Roche Diagnostics, Mannheim, Germany; detection limit 12 IU/mL). The presence of YMDD mutation in the HBV polymerase gene was analyzed by PCR assay and bidirectional DNA sequencing.
Patient characteristics were compared by using the analysis of variance (ANOVA) or chi-square test, and the durations of HBV-DNA titer decrement were analyzed by using the ANOVA procedure. Cumulative treatment responses according to HBV-DNA titer decrement were compared by using the chi-square test or Fisher exact test. SPSS (version 17.0, SPSS Inc, Chicago, IL) was used for statistical work and P < 0.05 was considered as statistically significant. The P value of pairwise post-hoc comparison was calculated by the Bonferroni method when the ANOVA result was significant.
The baseline characteristics of the LAM+ADV (n = 8) group, ETV (n = 8) group, and ADV (n = 11) group are compared in Table 1. Age, sex, and baseline laboratory characteristics including serum ALT and serum HBV-DNA levels were similar in all the 3 groups. The prevalence and location of LAM resistance mutations also showed no significant differences between the 3 groups (Table 2). Most patients (62.5%) in the LAM+ADV group had both rtL180M and rtM204V/I mutations, whereas only 2 patients (25.0%) in the ETV group had both rtL180M and rtM204V/I mutations. All of the patients showed genotype C.
The mean durations for HBV-DNA titer decrement (>1 log10 IU/mL) were 1.4 ± 0.9 months in the LAM+ADV group, 1.5 ± 1.3 months in the ETV group, and 1.5 ± 1.3 months in the ADV group (P = 0.104, Table 3). The mean durations for HBV-DNA titer decrement (>2 log10 IU/mL) were 2.6 ± 3.3 months in the LAM+ADV group, 1.9 ± 2.2 months in the ETV group, and 9.2 ± 7.3 months in the ADV group (P = 0.008, Table 3). The mean durations for HBV-DNA clearance (<357 IU/mL) were 19.8 ± 30.5 months in the LAM+ADV group, 9.0 ± 6.4 months in the ETV group, and 20.4 ± 8.6 months in the ADV group (P = 0.346, Table 3). The therapeutic period for HBV-DNA titer decrement (>2 log10 IU/mL) was significantly shorter in both the LAM+ADV group and the ETV group than in the ADV group (P = 0.008); however, there was no significant difference in the therapeutic period for HBV-DNA titer decrement (>2 log10 IU/mL) between the LAM+ADV group and the ETV group.
The rate of primary nonresponse, defined as <2 log10 IU/mL decrement in HBV-DNA titer at 24 weeks of therapy, was similarly low in both the LAM+ADV group and the ETV group compared to the ADV group (12.5%, 12.5%, and 63.6%, respectively, P = 0.022, Table 4). The rate of virologic response, defined as decrement in HBV-DNA titer to undetectable levels, was similarly high in both the LAM+ADV group and the ETV group compared to the ADV group at 24 weeks after treatment (50%, 37.5% vs 0%, P = 0.029, Table 5).
ALT Normalization and HBeAg Seroconversion Rate
Elevated ALT was noted in 2 of 8 patients in the LAM+ADV group, 4 of 8 patients in the ETV group, and 8 of 11 patients in the ADV group at the time of protocol change because of LAM resistance. The mean durations for ALT normalization were 5.5 ± 4.2 months in the LAM+ADV group, 3.8 ± 1.0 months in the ETV group, and 3.1 ± 1.8 months in the ADV group; however, statistical analysis was difficult because of small numbers of patients in those 3 groups.
HBeAg seroconversion occurred in 1 patient after 6.1 months in the LAM+ADV group, in 2 patients after 0.8 and 12.9 months in the ETV group, and in 3 patients after 22.4, 27.5, and 37.4 months in the ADV group; however, statistical analysis was difficult because follow-up period of LAM+ADV and ETV group was relatively short and the numbers of patients were small to compare.
The treatments were generally well tolerated in most of the patients. Three (1 patient in each group) patients experienced unknown transient microscopic hematuria. In the total 27 patients, no patient experienced a virologic or biochemical breakthrough during continued treatment with LAM+ADV or ETV (mean period; LAM+ADV 30.0 ± 9.8 months, ETV 25.3 ± 12.9 months, ADV 37.7 ± 21.4 months).
A rescue therapy should be considered by adding a second drug without cross-resistance or switching to a more potent drug. In adults, as a rescue therapy for patients with CHB with LAM resistance, 2009 AASLD guidelines recommended adding adefovir or tenofovir or switching to Truvada (a combination pill containing emtricitabine and tenofovir). 2009 EASL guidelines recommended adding tenofovir or adefovir (if tenofovir is not yet available); however, there are no treatment guidelines for pediatric patients. Moreover, tenofovir and emtricitabine have not yet been approved by the FDA for the treatment of CHB in children. According to the expert meeting report, the management of LAM-resistant chronic hepatitis in pediatric patients is determined by the severity of liver disease. Treatment may be stopped in nonsevere cases and the child monitored for flare-up, or if hepatitis is severe, a second antiviral drug such as adefovir can be added or treatment can be changed to IFN (9).
Combination therapy reduced the risk of developing adefovir resistance and hepatitis flare-up, and it is also more effective in HBV suppression than in ADV alone (1,10–13). Furthermore, early add-on therapy is more effective than late add-on therapy (14). Recent studies showed that low basal viral load had an influence on complete virologic response (10,15,16). Inadequate virologic suppression may lead to the emergence of resistant strains because of high viral load, which requires long-term treatment, so that viral breakthrough could develop eventually.
Our results confirm the findings of previous studies in adults by demonstrating that LAM+ADV combination therapy was effective. The rate of virologic response was 50% (4/8) at 24 weeks after treatment and 62.5% (5/8) at 36 weeks after treatment. These results are similar to those of studies in adults (10,11,17). In addition, LAM+ADV combination therapy or ETV monotherapy was superior to ADV monotherapy in terms of HBV-DNA clearance rate and HBV-DNA titer decrement >2 log10.
Entecavir is a more potent and effective agent with a high genetic barrier to resistance in nucleoside-naive patients (6,16,18–20); however, the entecavir resistance rate increased to 51% after 5-year treatment in LAM-refractory patients (21), and therefore entecavir may be considered inappropriate for treatment in patients with LAM resistance. From the HBV suppression point of view, it is interesting to note that the results of the present study in children are relatively better than those of the previous studies in adults (11,17,22). In the present study, the rate of virologic response was 37.5% (3/8) at 24 weeks and 50.0% (4/8) at 48 weeks, whereas the studies in adults showed a virologic response rate of 7.7% to 33.3% at 24 weeks and 22.0% to 54.5% at 48 weeks, in spite of the relatively higher baseline HBV-DNA load in the present study. Until now, there are only a few studies that evaluated the efficacy of LAM+ADV combination therapy or entecavir monotherapy in children with LAM-resistant CHB infection and our study demonstrated that LAM+ADV combination therapy and entecavir monotherapy was significantly superior to ADV monotherapy in terms of HBV-DNA clearance rate after 24 weeks (50%, 37.5% vs 0%, P = 0.029) and the rate of virologic response after 24 weeks (87.5%, 87.5% vs 36.4%, P = 0.022). Also, the therapeutic period for HBV-DNA titer decrement of more than 2 logs appeared to be shorter in the LAM+ADV combination group and the ETV group than in the ADV group (2.6 ± 3.3 months, 1.9 ± 2.2 months vs 9.2 ± 7.3 months, P = 0.008).
It is necessary to recognize the initial genotypic viral resistance before deciding upon the treatment option for achieving the most effective response. According to the 2-hit mechanism of entecavir resistance, entecavir has a high genetic barrier to wild-type HBV resistance, but there is a reduced susceptibility of the LAM-resistant virus to entecavir because the virus has already undergone 2 substitutions (rtL180M, rtM204V/I) for the development of entecavir resistance (23–25). Therefore, it is appropriate that the patients who had both LAM resistance mutations (180, 204) were treated with LAM+ADV combination therapy instead of entecavir montherapy; however, the Korean National Medical Insurance covers entecavir for patients who are older than 16 years until date and adefovir for patients who are older than 18 years before October 2010. Tenofovir is an effective alternative for the treatment of adult patients with LAM-resistant HBV infection (26). Add-on tenofovir to LAM is presently recommended for those patients by 2009 EASL guidelines and 2009 AASLD guidelines (1,7). The phase 3 clinical trial of entecavir and tenofovir in children is ongoing.
The present study has some limitations such as the relatively small number of patients and the selection bias. There may be a bias in the drug allocation process as the number of mutations and the patient's age were taken into consideration from the point of view of medical insurance coverage. Patients who had both LAM resistance mutations, rtL180M and rtM204V/I, received the LAM+ADV combination therapy except for 2 patients. Patients with only 1 LAM resistance mutation rtM204V/I received ETV monotherapy if they were covered by the medical insurance at the enrollment time (younger than 16 years old) or could be covered soon in the course of treatment.
In conclusion, the present study demonstrates more effective virologic responses with the use of both add-on adefovir with ongoing LAM or switching to entecavir monotherapy than those with the use of ADV monotherapy in children and adolescents with LAM-resistant CHB. Entecavir or tenofovir could be the first option in the near future because of the risk of using LAM in pediatric patients in the view of the frequent resistance and the difficulty of management with presently licensed drugs for children.
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