Adefovir Dipivoxil, tablet, 10 mg, Hepsera®, July 2006
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Public Summary Document
Product: Adefovir Dipivoxil, tablet, 10 mg, Hepsera®
Sponsor: Gilead Sciences Pty Ltd
Date of PBAC Consideration: July 2006
1. Purpose of Application
The submission sought an extension of the current Section 100 (Highly Specialised
Drug) listing for patients with active chronic hepatitis B to include the treatment
in combination with lamivudine of nucleoside therapy naïve patients with advanced
liver disease, and liver transplant patients with a history of HBV infection.
2. Background
A submission for a Section 100 (Highly Specialised Drug) listing for adefovir dipivoxil
tablet 10 mg was first considered by the PBAC at its December 2003 meeting. The PBAC
rejected the submission because of uncertainty over the extent of clinical benefit
and uncertain cost-effectiveness in the lamivudine-resistant hepatitis B population.
The Committee considered a re-submission at its July 2004 meeting and recommended
listing for second-line treatment of chronic hepatitis B on the basis of high but
acceptable cost-effectiveness compared with on-going ‘failed’ lamivudine therapy (100
mg daily). The PBAC noted that there was a clinical need for this drug for patients
who have failed therapy with lamivudine.
At the November 2005 meeting, the PBAC agreed to the sponsor’s request to remove the
requirement for a second liver biopsy based on adefovir dipivoxil’s listing as second-line
to lamivudine therapy which already requires patients to have a diagnosis of hepatitis
based on a liver biopsy. In order to overcome the concern that some patients may have
received non-PBS subsidised lamivudine therapy without having undergone a liver biopsy,
the PBAC recommended the addition of a note to the adefovir restriction stating that
patients should have had a liver biopsy at some point since original diagnosis.
3. Registration Status
Adefovir dipivoxil tablets 10 mg are TGA registered for marketing in Australia for:
The treatment of chronic hepatitis B in adults with evidence of active viral replication and either evidence of persistent elevations in serum aminotransferases (ALT or AST) or histologically active disease.
4. Listing Requested and PBAC’s view
Private Hospital Authority Required
Patients with active chronic hepatitis B (HBe antigen positive and/or serum HBV DNA
positive) who satisfy the following criteria:
- Advanced liver disease with either evidence of cirrhosis on liver biopsy or a Child-Pugh-Turcotte score > 5. Adefovir may be used as either as monotherapy or in combination with lamivudine; OR
- Repeatedly elevated (greater than 1.2 times the upper limit of normal) serum ALT levels while on concurrent antihepadnaviral therapy of greater than or equal to 6 months duration and no evidence of cirrhosis. Patients without evidence of cirrhosis may receive treatment in combination with lamivudine for the initial 3 months only of PBS-subsidised adefovir dipivoxil therapy. Patients who are immunosuppressed may receive treatment in combination with lamivudine for the initial 12 months of PBS subsidised adefovir therapy. Thereafter, PBS-subsidised adefovir dipivoxil must be used as monotherapy;
Patients with prior liver transplant and history of HBV infection. Adefovir may be
used as either as monotherapy or in combination with lamivudine.
NOTE:
Patients should have undergone a liver biopsy at some point since initial diagnosis
to obtain histological evidence of chronic hepatitis.
Female patients of child bearing age are not pregnant, not breast-feeding, and are
using an effective form of contraception.
Persons with Child’s class B or C cirrhosis (ascites, variceal bleeding, encephalopathy,
albumin less than 30g per L, bilirubin greater than 30 micromoles per L) should have
their treatment discussed with a transplant unit prior to initiating therapy.
The PBAC considered that the wording of the requested restriction did not exclude
the possibility of the use of adefovir monotherapy in patients with advanced liver
disease or in patients with prior liver transplant and history of hepatitis B virus
infection. Further, to remain consistent with the current listing the requested restriction
should also specify that patients who have repeatedly elevated (greater than 1.2 times
the upper limit of normal) serum ALT levels while on concurrent antihepadnaviral therapy
of greater than or equal to 6 months duration and no evidence of cirrhosis have failed
lamivudine therapy. However, the PBAC noted that the Pre-Sub-Committee and Pre-PBAC
Responses acknowledged that it would be inappropriate to allow adefovir monotherapy
in patients with advanced liver disease and post-transplant, and indicated willingness
to engage in further discussions about necessary amendments to the wording of any
restriction.
5. Clinical place for the proposed therapy
Combination use with lamivudine in patients with advanced liver disease or with a
prior liver transplant to reduce the risk of resistance development in these patients.
6. Comparator
The submission nominated the comparators for different disease stages as detailed in the table below.
Type of chronic hepatitis B population | Stage in the treatment pathway | Comparator |
---|---|---|
Advanced liver disease a |
Nucleos(t)ide-naive |
Lamivudine and sequential adefovir |
Advanced liver disease a |
Nucleos(t)ide-experienced |
Lamivudine and sequential adefovir |
Advanced liver disease a |
Nucleos(t)ide-experienced and lamivudine resistant |
Adefovir monotherapy |
Post-liver transplant |
Nucleos(t)ide-experienced |
Lamivudine and sequential adefovir |
Post-liver transplant |
Nucleos(t)ide-experienced and lamivudine resistant |
Adefovir monotherapy |
a defined as evidence of cirrhosis on liver biopsy or a Child-Pugh-Turcotte score
>5. Advanced liver disease therefore includes patients with compensated cirrhosis
and decompensated cirrhosis.
For PBAC’s view, see Recommendation and Reasons.
7. Clinical Trials
The scientific basis of comparison was:
- One head-to-head randomised comparative trial (NUC20912) comparing adefovir and lamivudine given in combination, and lamivudine monotherapy in nucleos(t)ide-naïve chronic hepatitis B patients with compensated liver disease (this trial was not published at the time of the submission); and
- data from a long-term resistance surveillance program conducted by the sponsor in chronic hepatitis B patients who have completed five clinical studies.
The PBAC was advised the subject group in the key trial was not representative of
those for whom PBS listing was sought. The trial data was predominantly derived from
HBeAg-positive (which usually is associated with better outcomes), compensated (better
outcomes), nucleos(t)ide-naïve patients only (but not post transplant); whereas the
population for whom PBS listing was sought is patients with advanced liver disease
or with prior liver transplant. Additionally the key trial did not compare lamivudine
and adefovir combination with lamivudine and sequential adefovir, the appropriate
comparator for nucleos(t)ide-naïve chronic hepatitis B patients with compensated liver
disease. The Pre-Sub-Committee Response argued that what is important is not the stage
of the disease but the fact that these drugs in combination actually suppress Hepatitis
B virus DNA turnover and reduce the amount of resistance.
8. Results of Trials
The results of the pivotal clinical trial showed proportionally more patients in the
adefovir and lamivudine combination arm achieved undetectable HBV DNA, HBeAg loss
and HbeAg seroconversion compared with the lamivudine arm at week 128 although statistical
testing was not performed. Adefovir and lamivudine combination reported numerically
greater effectiveness (although not statistically significant) for all virological,
histological and biochemical endpoints at week 128 compared with lamivudine monotherapy.
There was a statistically significant difference between adefovir and lamivudine combination
and lamivudine monotherapy in the development of YMDD resistance mutations at week
52 and week 104.
Serious adverse events were reported in higher numbers of patients in the lamivudine
monotherapy group compared with the adefovir plus lamivudine combination group, mainly
related to elevations in liver enzymes that may reflect differences in efficacy between
monotherapy and combination therapy. However, hepatitis flares wrere reported in a
greater proportion of subjects in the adefovir and lamivudine combination group than
in the lamivudine monotherapy group.
9. Clinical Claim
The submission described adefovir and lamivudine combination therapy as having significant
advantages in effectiveness over the main comparator and similar or less toxicity.
The PBAC accepted that adefovir and lamivudine combination therapy has significant
advantages in effectiveness over lamivudine and similar or less toxicity, in terms
of development of resistance as an intermediate indicator of effectiveness. However,
the relevance of this result derived from a population that does not reflect the population
for whom PBS listing is sought and from an incorrect comparator was considered uncertain.
10. Economic Analysis
A preliminary economic evaluation was presented. The resources included were drug
costs only. The trial-based incremental cost per extra patient avoiding lamivudine
resistance was estimated to be in the range of $45,000 - $ 75,000 in Year 2. The trial-based
incremental cost per extra patient avoiding adefovir resistance was estimated to be
in the range of $105,000 - $200,000 in Year 2.
A modelled economic evaluation was presented. The choice of the cost-effectiveness
approach is valid, but it was not completely applied as the submission did not report
these results in terms of the conventional measures, namely incremental cost per life-year
gained or per QALY gained. The PBAC noted a modelled evaluation to final outcomes
is necessary to calculate the cost/ QALY for the different populations requested in
the extension to the PBS listing i.e. advanced liver disease and post-transplant patients.
The risk of morbidity and mortality in these patient groups is likely to vary and
therefore produce different ICERs.
The base case modelled incremental cost per extra patient with dual resistance avoided
was estimated to be in the range $15,000 - $45,000. The base case modelled incremental
cost per extra patient-year of dual resistance avoided was estimated to be < $15,000.
11. Estimated PBS Usage and Financial Implications
The submission estimated a total in the range of 10,000 – 50,000 lamivudine prescriptions
and < 10,000 adefovir prescriptions in Year 4. The PES advised that these estimates
are reasonable.
The submission estimated a cost of < $10 million in year 4. There is potential for
usage beyond the requested restriction as adefovir monotherapy and adefovir and lamivudine
combination could be used to treat patients without advanced liver disease.
12. Recommendation and Reasons
The PBAC considered that the wording of the requested restriction did not exclude
the possibility of the use of adefovir monotherapy in patients with advanced liver
disease or in patients with prior liver transplant and history of hepatitis B virus
infection. Further, to remain consistent with the current listing the requested restriction
should also specify that patients who have repeatedly elevated (greater than 1.2 times
the upper limit of normal) serum ALT levels while on concurrent antihepadnaviral therapy
of greater than or equal to 6 months duration and no evidence of cirrhosis have failed
lamivudine therapy. However, the PBAC noted that the Pre-Sub-Committee and Pre-PBAC
Responses acknowledged that it would be inappropriate to allow adefovir monotherapy
in patients with advanced liver disease and post-transplant, and indicated willingness
to engage in further discussions about necessary amendments to the wording of any
restriction.
The PBAC also noted that the subject group in the key trial was not representative
of those for whom PBS listing was sought. The trial data were predominantly derived
from HBeAg-positive, compensated, nucleos(t)ide-naïve patients only (but not post
transplant); whereas the population for whom PBS listing was sought was for patients
with advanced liver disease or with prior liver transplant. Despite arguments in the
Pre-Sub-Committee and Pre-PBAC Responses that the stage of the disease is not relevant
in the development of resistance and that the long term outcomes of the development
of resistance would be worse in patients with advanced disease, insufficient evidence
was presented to support these hypotheses.
Additionally the key trial did not compare lamivudine and adefovir combination with
lamivudine and sequential adefovir, the appropriate comparator for nucleos(t)ide-naïve
chronic hepatitis B patients with compensated liver disease. The PBAC considered that
these issues with the subject group and the comparator in the clinical trial led to
considerable uncertainty about the interpretation of the clinical trial results.
The results for the primary and secondary surrogate outcomes from trial NUC20912 (time
weighted average change in serum HBV DNA from baseline to week 16 (primary outcome),
proportion of patients with ALT normalisation after 1 and 2 years of treatment (secondary
outcome) and proportion of patients with HBeAg loss and HBeAg seroconversion (secondary
outcomes)) suggest that there are no differences between a regimen in which adefovir
is added to lamivudine in comparison with lamivudine alone. Adefovir and lamivudine
combination was statistically more effective than lamivudine monotherapy in the development
of YMDD variant hepatitis B virus (secondary endpoint) at Week 104. The Pre-Sub-Committee
Response stated that the outcome of trial NUC20912 most relevant to the current submission
is the development of antiviral resistance (pre-specified, secondary outcome). The
submission argued that combination therapy with lamivudine and adefovir will delay
or prevent the development of clinically relevant antiviral resistance, and consequently
will delay disease progression in treated patients. This assumed a relationship between
the surrogate outcome of resistance and clinically relevant health outcomes, which
although plausible and supported by the presenter at the hearing, was not substantiated
by clinical trials.
The PBAC accepted that adefovir and lamivudine combination therapy has significant
advantages in effectiveness over lamivudine and similar or less toxicity, in terms
of development of resistance as an intermediate indicator of effectiveness. However,
the relevance of this result derived from a population that does not reflect the population
for whom PBS listing is sought and from an incorrect comparator was considered uncertain.
There were a number of uncertainties about the modelled economic evaluation, highlighted
by the PES commentary and the ESC Advice. These mainly resulted from the clinical
uncertainties, ie the concerns about the population in the model which does not represent
the patients for whom PBS listing is sought; the modelling of intermediate outcomes
rather than final outcomes and the absence of comparative data concerning incremental
LYG or incremental QALYs; and the uncertainty of the impact of resistance rates on
longer-term clinical sequelae and the ICERs for different sub-groups of chronic hepatitis
B patients, given the different baseline risks for morbidity and mortality in these
sub-groups.
The PBAC therefore rejected the submission because the patients did not reflect the
population requested in the restriction, the comparator in the key clinical trial
was not relevant to the current PBS treatment algorithm, and the uncertainty between
antiviral resistance and longer-term clinical outcomes. These problems led to uncertainty
about the clinical claim and in the economic model.
13. Context for Decision
The PBAC helps decide whether and, if so, how medicines should be subsidised in Australia.
It considers submissions in this context. A PBAC decision not to recommend listing
or not to recommend changing a listing does not represent a final PBAC view about
the merits of the medicine. A company can resubmit to the PBAC or seek independent
review of the PBAC decision.
14. Sponsor’s Comment
The sponsor acknowledges the PBAC comments and concerns. The sponsor wishes to address these issues and will continue to work with the PBAC towards a mutually acceptable solution to the emerging problem of HBV drug resistance.