Summary

More than 400 million people worldwide are chronically infected by the hepatitis B virus and the majority of these are Asians. Major breakthroughs have been achieved in the diagnosis and treatment of this virus. The currently available therapeutic agents include interferon, lamivudine, and adefovir dipivoxil. They rarely eradicate the virus, but greatly reduce its replication, necroinflammatory histological activity, and the progression of liver fibrosis. Their indications and uses are discussed in detail in this article. Some of the therapeutic agents under clinical trials at present are also described.

摘要

全世界超過4億人口感染了乙型肝炎病毒，其中大部份是亞洲人。現在乙型肝炎病毒的診斷和治療方面都有很大的突破。治療藥物包括干擾素，拉米夫丁和adefovir dipivoxil，雖然他們很少能徹底清除病毒，卻能很大程度地減低病毒的複製。肝組織發炎壞死，和纖維化的發展。本文詳細討論藥物的適應症和使用方法，同時介紹一些尚在臨床試驗階段的新藥。

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Introduction

Hepatitis B remains a significant problem today with over 400 million people chronically infected with the hepatitis B virus (HBV) worldwide.^1,2 The majority of these subjects are Asians. There have been significant advances in the treatment of hepatitis B in the last decade with the advent of nucleoside analogues and interferon. The primary treatment objectives are to

1. Stop HBV replication, ideally permanently;
2. Improve condition of the liver with normalisation of ALT and improvement in the liver histology;
3. Arrest and reverse hepatic fibrosis, thus improving long-term prognosis;
4. Stop progressive liver damage and cirrhosis;
5. Prevent HBV related complications e.g. hepatocellular carcinoma; and
6. Prolong life.

Who should be considered for treatment?^3-5

1. Patients who are hepatitis B surface antigen (HBsAg) positive, hepatitis B e antigen (HBeAg) positive and who have serum alanine aminotransferase (ALT) >2 x upper limit of normal (ULN) should be monitored for 3-6 months for spontaneous seroconversion. If after 3-6 months, ALT remains >2 x ULN they should then be considered for treatment if their HBV DNA levels are >10⁵ copies/ml.
2. Those patients who are HBsAg positive and HBeAg negative with HBV DNA >10⁵ copies/ml and ALT >2 x ULN on repeated testing.
3. Those patients who have compensated or decompensated hepatitis B cirrhosis and HBV DNA >10⁵ copies/ml.

However, there is emerging evidence that patients with ALT <2 x ULN may still be at risk of long term complications such as cirrhosis or hepatocellular carcinoma.¹ Whether these patients should be considered for treatment is still to be determined, and this is probably dependent on the discovery of a treatment regime which is safe and unlikely to give rise to resistance, since patients with normal or near normal ALT levels would require longer periods of treatment compared to those with higher ALT levels.

Measurement of HBV DNA in serum¹

HBV DNA assays are becoming more popular and accessible. However, HBV DNA assays are limited by a lack of standardisation and cost. The commonly used commercial assays for HBV DNA concentrations are branched DNA assay (Versant) and hybrid capture test (Digene Hybrid Capture). The lower limits of detection for these two assays are 700000 copies/ml and 140000 copies/ml, respectively. The polymerase chain reaction (PCR) assays (e.g. Amplicor or Taqman) allow for detection of 50-300 copies/ml. Although a HBV DNA concentration of fewer than 10⁵ copies/ml has been described as associated with HBeAg seroconversion and inactive disease, recent studies have shown that there is no cut off level of HBV DNA concentration for inactive disease. Furthermore, after 6 months of lamivudine, patients with HBV DNA concentrations of more than 10³ copies/ml have a 63% chance of subsequently developing lamivudine resistance, whereas those with concentrations of 10³ copies/ml or fewer have only a 13% chance.² Thus, quantitative PCR should ideally be used for monitoring the progression of disease and the effectiveness of treatment. This is especially important since at least two of the future nucleoside analogues, entacavir and telbivudine, can lower the HBV DNA levels to below PCR detectability in a large proportion of patients. However using quantitative PCR assays would increase the cost of follow-up considerably.

Is liver biopsy necessary?

Liver biopsy has been recommended for baseline assessment before the commencement of therapy.⁶ Liver biopsy is useful for the assessment of the severity of hepatitis and can identify any other concurrent liver diseases, such as steatohepatitis. However, there is a risk of significant complication together with pain or discomfort with liver biopsy. Sampling errors affect its accuracy. In the presence of abnormal liver biochemistry (ALT >2 x ULN) and HBV DNA >10⁵ copies/ml, liver histology does not affect the management significantly. Liver biopsy should definitely be considered in patients when there is any suggestion of concomitant liver diseases.^1-3 If liver biopsy is being contemplated, the patient should be advised fully on the benefits, limitations, risks and discomfort associated with this procedure.

Treatment options

Currently, only 3 therapeutic agents have been approved and marketed. These include nucleoside/nucleotide analogues lamivudine and adefovir diprivoxil, and interferon alfa (IFN-). Liver transplantation is effective and should be considered in patients with end-stage decompensated liver disease.

Nucleoside/Nucleotide analogues

Lamivudine

It is the (-)enanatiomer of 2'-3'dideoxy-3'-thiacytidine, which acts by the incorporation of the active 3TC-TP into the growing DNA chain results in premature chain termination thereby inhibiting HBV DNA synthesis.^1,2

The usual dose is 100mg daily. Lamivudine is well tolerated with minimal side effects.

It has been shown to be effective in patients with elevated ALT. Around 16-18% of patients after 1 year of lamivudine will have HBeAg seroconversion compared with 4-6% of untreated controls. Histological improvement with reduction in necroinflammation was observed in 49-56% of patients compared with 23-25% of the controls.³ Pretreatment ALT level is the major predictor of response for HBeAg seroconversion. After one year of treatment with lamivudine, HBeAg seroconversion occurs in 2%, 7%, 20% and 42% of patients whose pretreatment ALT levels are within normal, 1-2 x ULN, 2-5 x ULN and >5 x ULN respectively.³

Lamivudine has also been shown to be effective in patients with HBeAg negative chronic hepatitis B with both biochemical and virological response (i.e. improvement in ALT levels and reduction in viral load).

Asian patients respond similarly to Caucasian patients.² Lamivudine is also shown to be safe and efficacious in those who has failed previous IFN-a treatment and in children with chronic hepatitis B.³

Recent studies in patients with decompensated hepatitis B cirrhosis have shown that lamivudine is well tolerated and results in clinical improvement in many patients.^2-4,7 Patients on the liver transplant waiting lists may no longer require liver transplantation after being treated with lamivudine. In a prospective placebo-controlled trial in patients with compensated cirrhosis, lamivudine has been shown to decrease the incidence of cirrhotic complications and hepatocellular carcinoma significantly. However, one of the major concerns with treatment is the selection of resistant strain, the tyrosine-methionine-aspartate-aspartate (YMDD) mutant HBV.

Duration of treatment

For those patients who are HBeAg positive, one of the recommended endpoints for treatment is HBeAg seroconversion (i.e. from HBeAg positivity to the development of antibodies against HBeAg (anti-HBe)). Durability of response is reported to be 38-77% and relapse (i.e. reversion to HBeAg positivity) is reduced if therapy is continued for at least 6 months after seroconversion.³

For those who have lost HBeAg but has no detectable anti-HBe, it is best to continue with lamivudine treatment. Treatment should be continued for those who have not achieved HBeAg seroconversion.

For those who are HBeAg negative to begin with, the duration of treatment is still controversial. If lamivudine is stopped after ALT normalization with HBV DNA levels below the detection limit of hybridization assay, the relapse rate is still very high. If lamivudine is continued indefinitely, there will be increasing risk for the development of resistant strain of HBV.

Lamivudine resistance

The major concern for long-term lamivudine is the selection of lamivudine-resistant mutants. The most common form of resistance mutation affects the YMDD motif of the HBV DNA polymerase (rtM204V/I) (i.e. substitution of methionine at position 204 to valine or isoleucine). There is a frequent accompanying mutation in the upstream region of the polymerase gene (rtL180M) (i.e. substitution of leucine to methionine). From pooled data of several large-scale trials, the incidence of YMDD mutants rises from 15-32% in the first year to 67-69% by the fifth year of treatment.²

The emergence of resistance strain can be accompanied by an increase in ALT which occasionally may precipitate hepatic decompensation. The risk of hepatitis flares increases with time after the development of YMDD mutants, being 77% four years after its development.⁶ However, about 30% of breakthrough infection could be attributed to non-compliance.³ Therefore, it is useful to confirm lamivudine resistance by sequencing or by performing a line-probe assay.

Special patients group

Children: the recommended dose is 3mg/kg/day

Dose reduction is necessary for those with poor renal function and creatinine clearance of <50ml/min.

Lamivudine 150mg twice daily is effective against HIV/hepatitis B co-infection in combination with other anti-retroviral agents.

Suggested monitoring during therapy

• Monitor liver function tests (LFTs) 4-8 weekly initially. Once the LFTs are stable, the patient should have at least 3-6 monthly LFTs.
• If LFTs are worsen during therapy, check for compliance and then for HBV DNA levels. If HBV DNA levels have risen, lamivudine resistance should be suspected and preferably confirmed by tests.

Adefovir dipivoxil

This is a nucleotide analog of adenosine monophosphate. Similar to lamivudine, it inhibits both the reverse transcriptase and DNA polymerase activity and is incorporated into HBV DNA causing chain termination.³

It has been shown to have similar efficacy to lamivudine in both HBeAg positive and HBeAg negative patients.² However, it has not yet been studied in children nor as a primary treatment in those with decompensated cirrhosis.

More importantly, adefovir has been shown to be effective against lamivudine-resistant HBV in compensated or decompensated liver disease and liver transplant recipients.³

The usual dose is 10mg daily and it is well tolerated. However, when adefovir was used at higher doses during its initial trials as an anti-HIV agent, it had been reported to cause renal tubular dysfunction resembling Fanconi syndrome with hypophosphataemia as well as deterioration in renal function. As a result, only 10mg daily dose was used for the treatment of hepatitis B. With this dose, no nephrotoxicity was seen after 48 weeks of treatment in the Phase III trial but nephrotoxicity was reported in 2.5% patients with compensated liver disease during the second year of therapy, in 12% transplant recipients, and in 28% patients with decompensated cirrhosis in their first year of treatment.³ Therefore, it is important to monitor renal function at least 3 monthly. It should be monitored more frequently in those who have renal insufficiency before treatment is started.

Duration of treatment and durability of response

There is no data on the duration and durability of response but preliminary data suggests that it is probably similar to lamivudine.

Adefovir resistance

Adefovir resistance was not observed after 12 months of treatment during the Phase III clinical trials but it was found in patients who received 24 months/extended course of treatment. The reported incidence is about 2.5% in the second year.⁴ This is much lower than that of lamivudine. Two mutations are reported. One is located downstream of the YMDD motif, rtN236T (i.e. asparagine to threonine) and one upstream, rtA181V (i.e. alanine to valine). Lamivudine is effective against both adefovir-resistant HBV mutants.²

Special patient groups

Dose interval should be increased in those with renal failure and creatinine clearance of <50ml/min.

Children: It has not yet been approved for use in children but trials in children will be carried out later this year.

Patient who has lamivudine resistance strain can be commenced on adefovir. It has been suggested that patients can stop lamivudine when adefovir is added but an overlap period of 4-12 weeks before stopping lamivudine is recommended since a hepatitis flare may occur in up to 38% of patients if lamivudine is stopped before adefovir begins to act.

Suggested monitoring during therapy

• Monitor LFTs 4-8 weekly initially. Once stable, should have at least 3-6 monthly LFTs.
• If LFTs worsen during therapy, check for compliance and then check for HBV DNA +/- adefovir resistance (only available in tertiary referral centre).

Interferon alpha (IFN-)

IFN- has been shown to be useful in a proportion of selected patients. It is administered by subcutaneous injections. It is shown to be useful in patients with high pretreatment ALT in causing HBeAg seroconversion. Overall sustained response can only be achieved in 15-30% of patients. However, virologic response is poor (<10% of patients) in those patients with normal ALT.³ It appears to be less effective in those patients who are anti-HBe positive with high relapse rate after cessation of treatment. A longer duration of treatment may improve the sustained response rate. It should be avoided in patients with Child's B or C cirrhosis as it can precipitate hepatic decompensation.³ On long-term follow up, Caucasian patients who lose HBeAg following IFN-a therapy have significantly better survival compared with those who are still HBeAg positive.² A large proportion (over 50%) also loses HBsAg. The data in Asian population is less promising.^2,3 It may be related to the fact that Asian patients acquire the hepatitis B at young age and thus have a prolonged immune tolerance phase. As a result they are less responsive to immunomodulating therapy. There has been report of steroid priming before IFN treatment to enhance its effect. However, steroid priming is potentially dangerous in HBV patients since it may cause severe, even fatal, hepatitic reactivation following withdrawal.³ It should not be a routine procedure.

The usual dose of IFN- is 5 million units (MU) daily or 10 MU 3 times weekly for adults and 6 MU/m² (maximum 10 MU) three times weekly for children.

Adverse events

One of the major drawbacks of IFN- treatment is its significant side effects. The most common symptoms that patient experienced include flu-like symptoms, fatigue and depression. The other side effects include anorexia, hair loss, mood swings and these may persist even after cessation of therapy. The mood disturbance may be serious enough to cause suicide attempts. It may also cause moderate thrombocytopenia and/or leucopenia, which will require dose adjustment. It can induce autoantibodies formation and cause thyroid dysfunction or idiopathic thrombocytopenic purpura. Therefore, careful monitoring of thyroid functions during therapy is required. A metanalysis has shown that up to 5% of patients required premature discontinuation of treatment because of side effects and up to 35% will require dose adjustment.³

Duration of treatment

For HBeAg positive patients, the recommended treatment duration is 16 weeks.

For HBeAg negative patients, the recommended treatment duration is 12 months.

Durability of response

IFN- induced HBeAg clearance has been reported to be durable in 80% of patients in a 4-8 years follow up but most patients remain HBV DNA positive by PCR assay if they remain positive for HBsAg.

Suggested monitoring

	Pretreatment:
	-	Complete blood picture, renal functions, LFTs and thyroid function tests (TFTs).
	-	A clear documentation of previous or concurrent psychiatric illnesses.
	During treatment:
	-	Weekly CBP, R/LFT initially for 4 weeks, and if stable can space out to 2-4 weekly until the end of treatment. Monthly TFTs during therapy.
	-	Monitor for side effects and psychiatric symptoms.
	After Treatment
	-	LFTs, TFTs, HBV DNA and hepatitis serology include HBeAg status at the end of treatment and 6 month after treatment.
	-	Monitor LFTs and AFP 6 monthly thereafter.

Other treatments^1,2

Entecavir

This is a carbocyclic analogue of 2'-deoxyguanosine. Like lamivudine, it inhibits the reverse transcription of negative strand of HBV DNA from the pregenomic RNA and the synthesis of the positive strand HBV DNA. In addition, it also inhibits the priming of HBV DNA polymerase which requires guanosine triphosphate. It appears to be more potent than lamivudine and adefovir in in vitro studies, and is currently in Phase III trials.

Tenofovir

This is an acylic nucleotide reverse transcriptase inhibitor which is approved as a treatment for HIV. It has only been studied in patients with HIV/hepatitis B co-infections and has been shown to be effective. It is possibly less nephrotoxic than adefovir although renal impairment has been reported. However, there is no long-term data on the treatment of HBV alone as yet.

Some of the nucleoside/nucleotide analogues currently under clinical trials include the following:

• Emtricitabine (FTC)
• L-nucleosides (LdT and LdC)
• Clevudine (L-FMAU)

Pegylated IFN-

Clinical trials are still ongoing. With 48 weeks of therapy, it appears to have slightly greater efficacy compared with standard IFN- therapy. The role of pegylated IFN- and its optimal dose and duration remains to be determined.

Thymosin

This is a synthetic polypeptide which stimulates T-cell maturation and its function. It requires subcutaneous injections. The data on its efficacy is conflicting. It should not be used for the treatment of hepatitis B except in a clinical trial setting.

Combination therapy

There are ongoing studies on various combinations of nucleoside/nucleotide analogues. Combination of lamivudine and pegylated IFN- has also been investigated. None of these combination studies has shown any additional benefit over monotherapy so far.² Combination therapy should therefore only be considered in clinical trials at this moment.

Recommendations of treatment are summarised as below:

• For those with normal or <2 x ULN ALT, the evidence at present suggests follow up. Treatment should only be considered once ALT becomes elevated.
• For those with elevated ALT of >2 x ULN, treatment could be considered.
• If the clinical condition is stable, it is advisable to follow them for 3 to 6 months as there may be spontaneous seroconversion.
• For those with decompensated disease, treatment with nucleoside/nucleotide analogues should be considered.
• If ALT remained elevated to >2 x ULN and patient is HBeAg positive with HBV DNA >10⁵ copies/ml, then patients could be considered for IFN, lamivudine or adefovir treatment. The choice of treatment depends on the patient, physician and local expertise. Other considerations should include the duration of treatment, cost, route, side effects and resistance.
• If ALT remained elevated to >2 x ULN and patient is HBeAg negative with HBV DNA >10⁵ copies/ml then long-term lamivudine and adefovir should be used. However, with lamivudine treatment, one should warn the patients about the possibility of resistance.

Who should be referred?

While monitoring of patients with chronic hepatitis B can easily be carried out in the primary care setting including 6 monthly LFTs, abdominal ultrasound with or without -fetoprotein (AFP) testing, treatment of hepatitis B is a difficult and evolving field. Treatment with IFN is particularly difficult because of its significant side effects. Thus, it is probably advisable to refer patients who are suitable for treatment and those with decompensated disease to a hepatologist for further opinion unless the treating doctor is familiar with the handling of these treatment regimes.

Key messages

1. More than 400 million people worldwide are chronically infected by the hepatitis B virus and the majority of these are Asians.
2. Treatment should be considered in patients with chronic hepatitis B and persistent elevated ALT of >2 x ULN with HBV DNA >10⁵ copies/ml.
3. There is emerging evidence that patients with ALT <2 x ULN may still be at risk of long term complications such as cirrhosis or hepatocellular carcinoma.
4. The current available therapeutic agents include nucleoside/neucleotide analogues (lamivudine and adefovir diprivoxil) and interferon alpha.
5. These agents rarely eradicate the virus, but can greatly reduce viral replication, necroinflammatory activity, and the progression of liver fibrosis. Most recently it has been proven to reduce the progression of cirrhosis.
6. Prolonged treatment with lamivudine is associated with the development of lamivudine-resistant mutants (YMDD) which are sensitive to adefovir dipivoxil.
7. Adefovir-resistant mutants have also been described but the incidence is much lower than with lamivudine.
8. IFN alpha appears to be less promising in Asian population.
9. None of the combination studies has shown any additional benefit over monotherapy so far.

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References