Apixaban for the prevention of venous thromboembolism in people ...

5.2.3 Population
The patient groups included in the economic evaluation are patients aged 18 years and over
who have undergone elective total hip or knee replacement surgery. Patients who have
undergone hip (THR) and knee (TKR) surgery are modelled separately to reflect the
differences in VTE risk, treatment duration, patient characteristics and to reflect the appraisal
scope. The populations used in the model are slightly younger and for TKR less often male
(Table 5.2).
Table 5.2: Comparison of age and gender of TKR and THR patients in apixaban trials
versus clinical practice (National Joint Registry) (based on Table 55 MS-page 127)
THR TKR
Advance 3 Clinical Advance 2 Clinical
practice
practice
Males 46.2–47.6% § 44% 26–30% § 43%
Age at initial surgery for males 65.89 # 68.26 #
Age at initial surgery for females 68.51 # 68.14 #
Age at initial surgery all 60.0–60.9* 65.1–66.0*
*Mean age in each arm of the trial; #Mean age; §% in each arm of the trial.
Comment
– According to the ERG the population is in line with the scope.
– The fact that a younger population was included in the apixaban trials compared to
clinical practice may impact the relative risks in the model. Sensitivity analyses were
performed on age, but in these analyses relative risks were not changed. The ERG feels
that the efficacy of apixaban compared to enoxaparin may have been overestimated,
because earlier studies showed that oral anticoagulants are potentially more effective in
younger patients. 21, 23, 24, 48 However, this also holds for rivaroxaban and dabigatran
compared to enoxaparin, and will therefore probably not affect the efficacy of apixaban
compared to the other new oral anticoagulants.
– The fact that the TKR population consisted of fewer males than is seen in clinical practice
may also influence the cost-effectiveness results. No sensitivity analyses were performed
in the manufacturer’s submission. In the clarification letter the ERG asked the
manufacturer to describe whether sex and age are predictors of bleeding and VTE. If so,
the manufacturer was asked to adjust baseline risks and relative risks in the model. The
manufacturer responded that statistically significant predictors such as age and sex were
not assessed because a small number of studies were available.
5.2.4 Interventions and comparators
The indication considered in the economic evaluation is the prevention of venous
thromboembolic events in adult patients who have undergone elective hip or knee
replacement surgery.
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